Idea: Public Access Modifier Respected in Type Definition

allevato · October 5, 2017, 5:05am

Trust me, I'm the last person who wants to rehash access levels in Swift
again. But that's not what's happening here, IMO, and fixing bugs is not
just "a change for the sake of changing."

The current behavior of "private extension" is *incorrect*, because it's
entirely inconsistent with how access levels on extensions are documented
to behave and it's inconsistent with how other access levels apply to
extensions.

Can anyone think of a reason—other than "it's too late to change it"—why
"private extension" and "fileprivate extension" should behave the same, and
why "X extension { decl }" should be identical to "extension { X decl }"
for all X *except* "private"?

Yes, it's absolutely unfortunate that this oversight was not addressed when
the other access level changes were made. But we shouldn't have to live
with bugs in the language because we're afraid of some unknown amount of
churn among code that is already written incorrectly. Nor is fixing this
bug declaring open season on other, unrelated access level debates. Do you
have data that shows that the amount of code broken because it's using
"private" when it really should be saying "fileprivate" is high enough that
we should just leave the bug there?

···

On Wed, Oct 4, 2017 at 9:51 PM Jose Cheyo Jimenez via swift-evolution < swift-evolution@swift.org> wrote:

There was a high bar for breaking changes in swift 4 and is even higher
for swift 5. se-110 was approved and implemented on the premises that it
was not a big change but it was breaking code so it got reverted. Sure the
migrator was making this easier but the result was a usability regression.
I think this is a change just for the sake of changing. This will cause
unnecessary churn. Let’s leave ACLs alone for the next few versions of
swift unless we have a way better system.

https://lists.swift.org/pipermail/swift-evolution-announce/2017-June/000386.html

On Oct 4, 2017, at 8:47 PM, BJ Homer <bjhomer@gmail.com> wrote:

It certainly could break *some* code. But it only breaks code written by
an author who wrote ‘private extension’ knowing that ‘fileprivate
extension’ was also an option, but still intended it to be shared with the
whole file. (If that code was from Swift 2, it would have already been
migrated to ‘fileprivate extension’ by the 2->3 migrator.)

So existing code that says ‘private extension’ was written in a Swift 3 or
4 era when ‘fileprivate’ was an option. If the goal was specifically to
share it with the whole file, it seems likely that most authors would have
used ‘fileprivate extension’ instead of ‘private extension’, as that better
communicates the intention. Regardless, though, we could check against the
Swift source compatibility test suite to see how widespread that is.

Regardless, I think this change makes Swift a better language, and I’m in
favor of it.

-BJ

On Oct 4, 2017, at 9:10 PM, Jose Cheyo Jimenez via swift-evolution < > swift-evolution@swift.org> wrote:

On Oct 2, 2017, at 9:59 PM, David Hart via swift-evolution < > swift-evolution@swift.org> wrote:

On 3 Oct 2017, at 05:12, Xiaodi Wu via swift-evolution < > swift-evolution@swift.org> wrote:

On Mon, Oct 2, 2017 at 9:16 PM, Matthew Johnson via swift-evolution < > swift-evolution@swift.org> wrote:

Sent from my iPad

On Oct 2, 2017, at 7:33 PM, Jordan Rose via swift-evolution < >> swift-evolution@swift.org> wrote:

On Oct 2, 2017, at 03:25, Vladimir.S via swift-evolution < >> swift-evolution@swift.org> wrote:

On 01.10.2017 1:18, Chris Lattner wrote:

On Sep 29, 2017, at 10:42 AM, Xiaodi Wu via swift-evolution < >> swift-evolution@swift.org> wrote:

Vladimir, I agree with you on that change, but it’s a separate topic from
this one.

Tony is absolutely correct that this topic has already been discussed. It
is a deliberate design decision that public types do not automatically
expose members without explicit access modifiers; this has been brought up
on this list, and it is clearly not in scope for discussion as no new
insight can arise this late in the game. The inconsistency with public
extensions was brought up, the proposed solution was to remove modifiers
for extensions, but this proposal was rejected. So, the final design is
what we have.

Agreed. The core team would only consider a refinement or change to
access control if there were something actively broken that mattered for
ABI stability.

So we have to live with *protected* extension inconsistency for very long
time just because core team don't want to even discuss _this particular_
inconsistency(when access level in *private extension* must be private, not
fileprivate)?

Yes, we decided that access level for extension will mean a default and
top most access level for nested methods, OK. But even in this rule, which
already differ from access modifiers for types, we have another one special
case for 'private extension'.

Don't you think this is not normal situation and actually there IMO can't
be any reason to keep this bug-producing inconsistency in Swift?
(especially given Swift 5 seems like is a last moment to fix this)

I hate to say it but I'm inclined to agree with Vladimir on this.
"private extension" has a useful meaning now distinct from "fileprivate
extension", and it was an oversight that SE-0169
<https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md> didn't
include a fix here. On this *very narrow, very specific *access control
issue I think it would still be worth discussing; like Xiaodi said it's not
related to James' original thread-starter.

I agree with this in principle but would not want to see it become a
slippery slope back into extremely long access control discussions.

As I've said elsewhere, I too agree with this in principle. I agree with
Jordan that the current state of things is justifiable but the alternative
would be somewhat superior, agree that in a vacuum this very narrow and
specific discussion might be warranted, and agree also that this could be a
very slippery slide down a very steep slope.

Same here. It’s the only grudge I have left with the current access
control situation. I remember Doug Gregor and John McCall discussing this
during the last access control proposal. And I wouldn’t mind having a very
narrow discussion about only this.

I organize my types into extensions for each conformance and for each
access control. I can currently implicitly apply public or fileprivate to
all members of an extension but I have no way of doing the same for
private. That’s why I think it should be fixed.

This will break a bunch of code because `private extension` has *always*
meant `fileprivate extension`. Even Swift 3 had this same behavior. Lowering
the access level of the extension members will hide a bunch of code that
was visible to the file.

169 was not a breaking change but this “fix” would have made it a breaking
change. I doubt 169 would had been accepted if it was a breaking change. I
don’t think it’s worth it.

https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md

(I maintain that the current model does *not* include a special case; it
simply means the 'private' is resolved at the level of the extension rather
than the level of its members. But that isn't what people expect and it's
not as useful.)

I agree that changing the behavior of *all* access modifiers on
extensions is out of scope. (I also agree that it is a bad idea. Sorry,
James, but wanting 'pubic' here indicates that your mental model of
extensions does not match what Swift is actually doing, and that could get
you into trouble.)

Jordan

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masters3d · October 5, 2017, 5:33am

I appreciate the enthusiasm but this is not a bug. This was a deliberate change in swift 3 to make `private extension` usable. If this was a bug then during swift 3 we should have disallowed `private extension` and only allowed `fileprivate extension` but that is not what happened. `private extension` has worked the same since swift 1. I’ve always used `private extension` when I want to add methods to String or other build in types.

private is different because it is scoped so because of that it is also different when dealing with extensions. Top level private is always the same as fileprivate thanks to its scoped nature.

Making private the scope ACL was a mistake but that ship has sailed and so has this one imo.

···

On Oct 4, 2017, at 10:05 PM, Tony Allevato <tony.allevato@gmail.com> wrote:

Trust me, I'm the last person who wants to rehash access levels in Swift again. But that's not what's happening here, IMO, and fixing bugs is not just "a change for the sake of changing."

The current behavior of "private extension" is *incorrect*, because it's entirely inconsistent with how access levels on extensions are documented to behave and it's inconsistent with how other access levels apply to extensions.

Can anyone think of a reason—other than "it's too late to change it"—why "private extension" and "fileprivate extension" should behave the same, and why "X extension { decl }" should be identical to "extension { X decl }" for all X *except* "private"?

Yes, it's absolutely unfortunate that this oversight was not addressed when the other access level changes were made. But we shouldn't have to live with bugs in the language because we're afraid of some unknown amount of churn among code that is already written incorrectly. Nor is fixing this bug declaring open season on other, unrelated access level debates. Do you have data that shows that the amount of code broken because it's using "private" when it really should be saying "fileprivate" is high enough that we should just leave the bug there?

On Wed, Oct 4, 2017 at 9:51 PM Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org> wrote:
There was a high bar for breaking changes in swift 4 and is even higher for swift 5. se-110 was approved and implemented on the premises that it was not a big change but it was breaking code so it got reverted. Sure the migrator was making this easier but the result was a usability regression. I think this is a change just for the sake of changing. This will cause unnecessary churn. Let’s leave ACLs alone for the next few versions of swift unless we have a way better system.

https://lists.swift.org/pipermail/swift-evolution-announce/2017-June/000386.html

On Oct 4, 2017, at 8:47 PM, BJ Homer <bjhomer@gmail.com> wrote:

It certainly could break *some* code. But it only breaks code written by an author who wrote ‘private extension’ knowing that ‘fileprivate extension’ was also an option, but still intended it to be shared with the whole file. (If that code was from Swift 2, it would have already been migrated to ‘fileprivate extension’ by the 2->3 migrator.)

So existing code that says ‘private extension’ was written in a Swift 3 or 4 era when ‘fileprivate’ was an option. If the goal was specifically to share it with the whole file, it seems likely that most authors would have used ‘fileprivate extension’ instead of ‘private extension’, as that better communicates the intention. Regardless, though, we could check against the Swift source compatibility test suite to see how widespread that is.

Regardless, I think this change makes Swift a better language, and I’m in favor of it.

-BJ

On Oct 4, 2017, at 9:10 PM, Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org> wrote:

On Oct 2, 2017, at 9:59 PM, David Hart via swift-evolution <swift-evolution@swift.org> wrote:

On 3 Oct 2017, at 05:12, Xiaodi Wu via swift-evolution <swift-evolution@swift.org> wrote:

On Mon, Oct 2, 2017 at 9:16 PM, Matthew Johnson via swift-evolution <swift-evolution@swift.org> wrote:

Sent from my iPad

On Oct 2, 2017, at 7:33 PM, Jordan Rose via swift-evolution <swift-evolution@swift.org> wrote:

On Oct 2, 2017, at 03:25, Vladimir.S via swift-evolution <swift-evolution@swift.org> wrote:

On 01.10.2017 1:18, Chris Lattner wrote:

On Sep 29, 2017, at 10:42 AM, Xiaodi Wu via swift-evolution <swift-evolution@swift.org> wrote:

Vladimir, I agree with you on that change, but it’s a separate topic from this one.

Tony is absolutely correct that this topic has already been discussed. It is a deliberate design decision that public types do not automatically expose members without explicit access modifiers; this has been brought up on this list, and it is clearly not in scope for discussion as no new insight can arise this late in the game. The inconsistency with public extensions was brought up, the proposed solution was to remove modifiers for extensions, but this proposal was rejected. So, the final design is what we have.

Agreed. The core team would only consider a refinement or change to access control if there were something actively broken that mattered for ABI stability.

So we have to live with *protected* extension inconsistency for very long time just because core team don't want to even discuss _this particular_ inconsistency(when access level in *private extension* must be private, not fileprivate)?

Yes, we decided that access level for extension will mean a default and top most access level for nested methods, OK. But even in this rule, which already differ from access modifiers for types, we have another one special case for 'private extension'.

Don't you think this is not normal situation and actually there IMO can't be any reason to keep this bug-producing inconsistency in Swift? (especially given Swift 5 seems like is a last moment to fix this)

I hate to say it but I'm inclined to agree with Vladimir on this. "private extension" has a useful meaning now distinct from "fileprivate extension", and it was an oversight that SE-0169 didn't include a fix here. On this very narrow, very specific access control issue I think it would still be worth discussing; like Xiaodi said it's not related to James' original thread-starter.

I agree with this in principle but would not want to see it become a slippery slope back into extremely long access control discussions.

As I've said elsewhere, I too agree with this in principle. I agree with Jordan that the current state of things is justifiable but the alternative would be somewhat superior, agree that in a vacuum this very narrow and specific discussion might be warranted, and agree also that this could be a very slippery slide down a very steep slope.

Same here. It’s the only grudge I have left with the current access control situation. I remember Doug Gregor and John McCall discussing this during the last access control proposal. And I wouldn’t mind having a very narrow discussion about only this.

I organize my types into extensions for each conformance and for each access control. I can currently implicitly apply public or fileprivate to all members of an extension but I have no way of doing the same for private. That’s why I think it should be fixed.

This will break a bunch of code because `private extension` has always meant `fileprivate extension`. Even Swift 3 had this same behavior. Lowering the access level of the extension members will hide a bunch of code that was visible to the file.

169 was not a breaking change but this “fix” would have made it a breaking change. I doubt 169 would had been accepted if it was a breaking change. I don’t think it’s worth it.

https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md

(I maintain that the current model does not include a special case; it simply means the 'private' is resolved at the level of the extension rather than the level of its members. But that isn't what people expect and it's not as useful.)

I agree that changing the behavior of all access modifiers on extensions is out of scope. (I also agree that it is a bad idea. Sorry, James, but wanting 'pubic' here indicates that your mental model of extensions does not match what Swift is actually doing, and that could get you into trouble.)

Jordan

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allevato · October 5, 2017, 5:59am

Yes, you're right about the history of "private extension"—I was forgetting
some of the details of what transpired during those proposals. Thanks for
the reminder.

That being said, I would still argue that it would be a shame if we decided
that the language should propagate a known inconsistency indefinitely
simply because it was overlooked during a proposal that could have fixed
it. I'd weigh the reduction of future user confusion as more valuable than
the cost for existing code to do a one-time migration, but that might be
easy for me to say because I don't use access levels on extensions at all
in my own code so I don't have any skin in the game.

···

On Wed, Oct 4, 2017 at 10:33 PM Jose Cheyo Jimenez <cheyo@masters3d.com> wrote:

I appreciate the enthusiasm but this is not a bug. This was a deliberate
change in swift 3 to make `private extension` usable. If this was a bug
then during swift 3 we should have disallowed `private extension` and only
allowed `fileprivate extension` but that is not what happened. `private
extension` has worked the same since swift 1. I’ve always used `private
extension` when I want to add methods to String or other build in types.

private is different because it is scoped so because of that it is also
different when dealing with extensions. Top level private is always the
same as fileprivate thanks to its scoped nature.

Making private the scope ACL was a mistake but that ship has sailed and so
has this one imo.

On Oct 4, 2017, at 10:05 PM, Tony Allevato <tony.allevato@gmail.com> > wrote:

Trust me, I'm the last person who wants to rehash access levels in Swift
again. But that's not what's happening here, IMO, and fixing bugs is not
just "a change for the sake of changing."

The current behavior of "private extension" is *incorrect*, because it's
entirely inconsistent with how access levels on extensions are documented
to behave and it's inconsistent with how other access levels apply to
extensions.

Can anyone think of a reason—other than "it's too late to change it"—why
"private extension" and "fileprivate extension" should behave the same, and
why "X extension { decl }" should be identical to "extension { X decl }"
for all X *except* "private"?

Yes, it's absolutely unfortunate that this oversight was not addressed
when the other access level changes were made. But we shouldn't have to
live with bugs in the language because we're afraid of some unknown amount
of churn among code that is already written incorrectly. Nor is fixing this
bug declaring open season on other, unrelated access level debates. Do you
have data that shows that the amount of code broken because it's using
"private" when it really should be saying "fileprivate" is high enough that
we should just leave the bug there?

On Wed, Oct 4, 2017 at 9:51 PM Jose Cheyo Jimenez via swift-evolution < > swift-evolution@swift.org> wrote:

There was a high bar for breaking changes in swift 4 and is even higher
for swift 5. se-110 was approved and implemented on the premises that it
was not a big change but it was breaking code so it got reverted. Sure the
migrator was making this easier but the result was a usability regression.
I think this is a change just for the sake of changing. This will cause
unnecessary churn. Let’s leave ACLs alone for the next few versions of
swift unless we have a way better system.

https://lists.swift.org/pipermail/swift-evolution-announce/2017-June/000386.html

On Oct 4, 2017, at 8:47 PM, BJ Homer <bjhomer@gmail.com> wrote:

It certainly could break *some* code. But it only breaks code written by
an author who wrote ‘private extension’ knowing that ‘fileprivate
extension’ was also an option, but still intended it to be shared with the
whole file. (If that code was from Swift 2, it would have already been
migrated to ‘fileprivate extension’ by the 2->3 migrator.)

So existing code that says ‘private extension’ was written in a Swift 3
or 4 era when ‘fileprivate’ was an option. If the goal was specifically to
share it with the whole file, it seems likely that most authors would have
used ‘fileprivate extension’ instead of ‘private extension’, as that better
communicates the intention. Regardless, though, we could check against the
Swift source compatibility test suite to see how widespread that is.

Regardless, I think this change makes Swift a better language, and I’m in
favor of it.

-BJ

On Oct 4, 2017, at 9:10 PM, Jose Cheyo Jimenez via swift-evolution < >> swift-evolution@swift.org> wrote:

On Oct 2, 2017, at 9:59 PM, David Hart via swift-evolution < >> swift-evolution@swift.org> wrote:

On 3 Oct 2017, at 05:12, Xiaodi Wu via swift-evolution < >> swift-evolution@swift.org> wrote:

On Mon, Oct 2, 2017 at 9:16 PM, Matthew Johnson via swift-evolution < >> swift-evolution@swift.org> wrote:

Sent from my iPad

On Oct 2, 2017, at 7:33 PM, Jordan Rose via swift-evolution < >>> swift-evolution@swift.org> wrote:

On Oct 2, 2017, at 03:25, Vladimir.S via swift-evolution < >>> swift-evolution@swift.org> wrote:

On 01.10.2017 1:18, Chris Lattner wrote:

On Sep 29, 2017, at 10:42 AM, Xiaodi Wu via swift-evolution < >>> swift-evolution@swift.org> wrote:

Vladimir, I agree with you on that change, but it’s a separate topic
from this one.

Tony is absolutely correct that this topic has already been discussed.
It is a deliberate design decision that public types do not automatically
expose members without explicit access modifiers; this has been brought up
on this list, and it is clearly not in scope for discussion as no new
insight can arise this late in the game. The inconsistency with public
extensions was brought up, the proposed solution was to remove modifiers
for extensions, but this proposal was rejected. So, the final design is
what we have.

Agreed. The core team would only consider a refinement or change to
access control if there were something actively broken that mattered for
ABI stability.

So we have to live with *protected* extension inconsistency for very
long time just because core team don't want to even discuss _this
particular_ inconsistency(when access level in *private extension* must be
private, not fileprivate)?

Yes, we decided that access level for extension will mean a default and
top most access level for nested methods, OK. But even in this rule, which
already differ from access modifiers for types, we have another one special
case for 'private extension'.

Don't you think this is not normal situation and actually there IMO
can't be any reason to keep this bug-producing inconsistency in Swift?
(especially given Swift 5 seems like is a last moment to fix this)

I hate to say it but I'm inclined to agree with Vladimir on this.
"private extension" has a useful meaning now distinct from "fileprivate
extension", and it was an oversight that SE-0169
<https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md> didn't
include a fix here. On this *very narrow, very specific *access control
issue I think it would still be worth discussing; like Xiaodi said it's not
related to James' original thread-starter.

I agree with this in principle but would not want to see it become a
slippery slope back into extremely long access control discussions.

As I've said elsewhere, I too agree with this in principle. I agree with
Jordan that the current state of things is justifiable but the alternative
would be somewhat superior, agree that in a vacuum this very narrow and
specific discussion might be warranted, and agree also that this could be a
very slippery slide down a very steep slope.

Same here. It’s the only grudge I have left with the current access
control situation. I remember Doug Gregor and John McCall discussing this
during the last access control proposal. And I wouldn’t mind having a very
narrow discussion about only this.

I organize my types into extensions for each conformance and for each
access control. I can currently implicitly apply public or fileprivate to
all members of an extension but I have no way of doing the same for
private. That’s why I think it should be fixed.

This will break a bunch of code because `private extension` has *always*
meant `fileprivate extension`. Even Swift 3 had this same behavior. Lowering
the access level of the extension members will hide a bunch of code that
was visible to the file.

169 was not a breaking change but this “fix” would have made it a
breaking change. I doubt 169 would had been accepted if it was a breaking
change. I don’t think it’s worth it.

https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md

(I maintain that the current model does *not* include a special case;
it simply means the 'private' is resolved at the level of the extension
rather than the level of its members. But that isn't what people expect and
it's not as useful.)

I agree that changing the behavior of *all* access modifiers on
extensions is out of scope. (I also agree that it is a bad idea. Sorry,
James, but wanting 'pubic' here indicates that your mental model of
extensions does not match what Swift is actually doing, and that could get
you into trouble.)

Jordan

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https://lists.swift.org/mailman/listinfo/swift-evolution

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hartbit · October 5, 2017, 11:32am

I appreciate the enthusiasm but this is not a bug. This was a deliberate change in swift 3 to make `private extension` usable. If this was a bug then during swift 3 we should have disallowed `private extension` and only allowed `fileprivate extension` but that is not what happened. `private extension` has worked the same since swift 1. I’ve always used `private extension` when I want to add methods to String or other build in types.

It’s not a bug, but its unfortunate the behaviour wasn’t changed at the same time as SE-0169, and it now is very inconsistent. I also don’t have to rehash previous discussions, but if a Core Team member (Chris) is okay with going ahead with this, perhaps we should consider it.

···

On 5 Oct 2017, at 07:34, Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org> wrote:

private is different because it is scoped so because of that it is also different when dealing with extensions. Top level private is always the same as fileprivate thanks to its scoped nature.

Making private the scope ACL was a mistake but that ship has sailed and so has this one imo.

On Oct 4, 2017, at 10:05 PM, Tony Allevato <tony.allevato@gmail.com <mailto:tony.allevato@gmail.com>> wrote:

Trust me, I'm the last person who wants to rehash access levels in Swift again. But that's not what's happening here, IMO, and fixing bugs is not just "a change for the sake of changing."

The current behavior of "private extension" is *incorrect*, because it's entirely inconsistent with how access levels on extensions are documented to behave and it's inconsistent with how other access levels apply to extensions.

Can anyone think of a reason—other than "it's too late to change it"—why "private extension" and "fileprivate extension" should behave the same, and why "X extension { decl }" should be identical to "extension { X decl }" for all X *except* "private"?

Yes, it's absolutely unfortunate that this oversight was not addressed when the other access level changes were made. But we shouldn't have to live with bugs in the language because we're afraid of some unknown amount of churn among code that is already written incorrectly. Nor is fixing this bug declaring open season on other, unrelated access level debates. Do you have data that shows that the amount of code broken because it's using "private" when it really should be saying "fileprivate" is high enough that we should just leave the bug there?

On Wed, Oct 4, 2017 at 9:51 PM Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
There was a high bar for breaking changes in swift 4 and is even higher for swift 5. se-110 was approved and implemented on the premises that it was not a big change but it was breaking code so it got reverted. Sure the migrator was making this easier but the result was a usability regression. I think this is a change just for the sake of changing. This will cause unnecessary churn. Let’s leave ACLs alone for the next few versions of swift unless we have a way better system.

https://lists.swift.org/pipermail/swift-evolution-announce/2017-June/000386.html

On Oct 4, 2017, at 8:47 PM, BJ Homer <bjhomer@gmail.com <mailto:bjhomer@gmail.com>> wrote:

It certainly could break *some* code. But it only breaks code written by an author who wrote ‘private extension’ knowing that ‘fileprivate extension’ was also an option, but still intended it to be shared with the whole file. (If that code was from Swift 2, it would have already been migrated to ‘fileprivate extension’ by the 2->3 migrator.)

So existing code that says ‘private extension’ was written in a Swift 3 or 4 era when ‘fileprivate’ was an option. If the goal was specifically to share it with the whole file, it seems likely that most authors would have used ‘fileprivate extension’ instead of ‘private extension’, as that better communicates the intention. Regardless, though, we could check against the Swift source compatibility test suite to see how widespread that is.

Regardless, I think this change makes Swift a better language, and I’m in favor of it.

-BJ

On Oct 4, 2017, at 9:10 PM, Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On Oct 2, 2017, at 9:59 PM, David Hart via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On 3 Oct 2017, at 05:12, Xiaodi Wu via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On Mon, Oct 2, 2017 at 9:16 PM, Matthew Johnson via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

Sent from my iPad

On Oct 2, 2017, at 7:33 PM, Jordan Rose via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On Oct 2, 2017, at 03:25, Vladimir.S via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On 01.10.2017 1:18, Chris Lattner wrote:

On Sep 29, 2017, at 10:42 AM, Xiaodi Wu via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

Vladimir, I agree with you on that change, but it’s a separate topic from this one.

Tony is absolutely correct that this topic has already been discussed. It is a deliberate design decision that public types do not automatically expose members without explicit access modifiers; this has been brought up on this list, and it is clearly not in scope for discussion as no new insight can arise this late in the game. The inconsistency with public extensions was brought up, the proposed solution was to remove modifiers for extensions, but this proposal was rejected. So, the final design is what we have.

Agreed. The core team would only consider a refinement or change to access control if there were something actively broken that mattered for ABI stability.

So we have to live with *protected* extension inconsistency for very long time just because core team don't want to even discuss _this particular_ inconsistency(when access level in *private extension* must be private, not fileprivate)?

Yes, we decided that access level for extension will mean a default and top most access level for nested methods, OK. But even in this rule, which already differ from access modifiers for types, we have another one special case for 'private extension'.

Don't you think this is not normal situation and actually there IMO can't be any reason to keep this bug-producing inconsistency in Swift? (especially given Swift 5 seems like is a last moment to fix this)

I hate to say it but I'm inclined to agree with Vladimir on this. "private extension" has a useful meaning now distinct from "fileprivate extension", and it was an oversight that SE-0169 <https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md> didn't include a fix here. On this very narrow, very specific access control issue I think it would still be worth discussing; like Xiaodi said it's not related to James' original thread-starter.

I agree with this in principle but would not want to see it become a slippery slope back into extremely long access control discussions.

As I've said elsewhere, I too agree with this in principle. I agree with Jordan that the current state of things is justifiable but the alternative would be somewhat superior, agree that in a vacuum this very narrow and specific discussion might be warranted, and agree also that this could be a very slippery slide down a very steep slope.

Same here. It’s the only grudge I have left with the current access control situation. I remember Doug Gregor and John McCall discussing this during the last access control proposal. And I wouldn’t mind having a very narrow discussion about only this.

I organize my types into extensions for each conformance and for each access control. I can currently implicitly apply public or fileprivate to all members of an extension but I have no way of doing the same for private. That’s why I think it should be fixed.

This will break a bunch of code because `private extension` has always meant `fileprivate extension`. Even Swift 3 had this same behavior. Lowering the access level of the extension members will hide a bunch of code that was visible to the file.

169 was not a breaking change but this “fix” would have made it a breaking change. I doubt 169 would had been accepted if it was a breaking change. I don’t think it’s worth it.

https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md

(I maintain that the current model does not include a special case; it simply means the 'private' is resolved at the level of the extension rather than the level of its members. But that isn't what people expect and it's not as useful.)

I agree that changing the behavior of all access modifiers on extensions is out of scope. (I also agree that it is a bad idea. Sorry, James, but wanting 'pubic' here indicates that your mental model of extensions does not match what Swift is actually doing, and that could get you into trouble.)

Jordan

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masters3d · October 5, 2017, 5:52pm

I appreciate the enthusiasm but this is not a bug. This was a deliberate change in swift 3 to make `private extension` usable. If this was a bug then during swift 3 we should have disallowed `private extension` and only allowed `fileprivate extension` but that is not what happened. `private extension` has worked the same since swift 1. I’ve always used `private extension` when I want to add methods to String or other build in types.

It’s not a bug, but its unfortunate the behaviour wasn’t changed at the same time as SE-0169, and it now is very inconsistent. I also don’t have to rehash previous discussions, but if a Core Team member (Chris) is okay with going ahead with this, perhaps we should consider it.

This could have not been part of 169 because it would've required to lower the visibility of the private extension modifier.

“No migration will be necessary as this proposal merely broadens the visibility of private.”

There was a corner case mentioned when dealing with functions with the same name and that was understandable.

private extension is consistent to the way the private scope rules work. The word private is explicit at the top level because extensions can only be declared at top level. Top level private is always fileprivate. The inconsistency is that we have 1 scope ALC and the rest are not. An explicit declaration should always take precedence when declaring something like an access level override.

···

On Oct 5, 2017, at 4:32 AM, David Hart <david@hartbit.com> wrote:

On 5 Oct 2017, at 07:34, Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

private is different because it is scoped so because of that it is also different when dealing with extensions. Top level private is always the same as fileprivate thanks to its scoped nature.

Making private the scope ACL was a mistake but that ship has sailed and so has this one imo.

On Oct 4, 2017, at 10:05 PM, Tony Allevato <tony.allevato@gmail.com <mailto:tony.allevato@gmail.com>> wrote:

Trust me, I'm the last person who wants to rehash access levels in Swift again. But that's not what's happening here, IMO, and fixing bugs is not just "a change for the sake of changing."

The current behavior of "private extension" is *incorrect*, because it's entirely inconsistent with how access levels on extensions are documented to behave and it's inconsistent with how other access levels apply to extensions.

Can anyone think of a reason—other than "it's too late to change it"—why "private extension" and "fileprivate extension" should behave the same, and why "X extension { decl }" should be identical to "extension { X decl }" for all X *except* "private"?

Yes, it's absolutely unfortunate that this oversight was not addressed when the other access level changes were made. But we shouldn't have to live with bugs in the language because we're afraid of some unknown amount of churn among code that is already written incorrectly. Nor is fixing this bug declaring open season on other, unrelated access level debates. Do you have data that shows that the amount of code broken because it's using "private" when it really should be saying "fileprivate" is high enough that we should just leave the bug there?

On Wed, Oct 4, 2017 at 9:51 PM Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
There was a high bar for breaking changes in swift 4 and is even higher for swift 5. se-110 was approved and implemented on the premises that it was not a big change but it was breaking code so it got reverted. Sure the migrator was making this easier but the result was a usability regression. I think this is a change just for the sake of changing. This will cause unnecessary churn. Let’s leave ACLs alone for the next few versions of swift unless we have a way better system.

https://lists.swift.org/pipermail/swift-evolution-announce/2017-June/000386.html

On Oct 4, 2017, at 8:47 PM, BJ Homer <bjhomer@gmail.com <mailto:bjhomer@gmail.com>> wrote:

It certainly could break *some* code. But it only breaks code written by an author who wrote ‘private extension’ knowing that ‘fileprivate extension’ was also an option, but still intended it to be shared with the whole file. (If that code was from Swift 2, it would have already been migrated to ‘fileprivate extension’ by the 2->3 migrator.)

So existing code that says ‘private extension’ was written in a Swift 3 or 4 era when ‘fileprivate’ was an option. If the goal was specifically to share it with the whole file, it seems likely that most authors would have used ‘fileprivate extension’ instead of ‘private extension’, as that better communicates the intention. Regardless, though, we could check against the Swift source compatibility test suite to see how widespread that is.

Regardless, I think this change makes Swift a better language, and I’m in favor of it.

-BJ

On Oct 4, 2017, at 9:10 PM, Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On Oct 2, 2017, at 9:59 PM, David Hart via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On 3 Oct 2017, at 05:12, Xiaodi Wu via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On Mon, Oct 2, 2017 at 9:16 PM, Matthew Johnson via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

Sent from my iPad

On Oct 2, 2017, at 7:33 PM, Jordan Rose via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On Oct 2, 2017, at 03:25, Vladimir.S via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On 01.10.2017 1:18, Chris Lattner wrote:

On Sep 29, 2017, at 10:42 AM, Xiaodi Wu via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

Vladimir, I agree with you on that change, but it’s a separate topic from this one.

Tony is absolutely correct that this topic has already been discussed. It is a deliberate design decision that public types do not automatically expose members without explicit access modifiers; this has been brought up on this list, and it is clearly not in scope for discussion as no new insight can arise this late in the game. The inconsistency with public extensions was brought up, the proposed solution was to remove modifiers for extensions, but this proposal was rejected. So, the final design is what we have.

Agreed. The core team would only consider a refinement or change to access control if there were something actively broken that mattered for ABI stability.

So we have to live with *protected* extension inconsistency for very long time just because core team don't want to even discuss _this particular_ inconsistency(when access level in *private extension* must be private, not fileprivate)?

Yes, we decided that access level for extension will mean a default and top most access level for nested methods, OK. But even in this rule, which already differ from access modifiers for types, we have another one special case for 'private extension'.

Don't you think this is not normal situation and actually there IMO can't be any reason to keep this bug-producing inconsistency in Swift? (especially given Swift 5 seems like is a last moment to fix this)

I hate to say it but I'm inclined to agree with Vladimir on this. "private extension" has a useful meaning now distinct from "fileprivate extension", and it was an oversight that SE-0169 <https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md> didn't include a fix here. On this very narrow, very specific access control issue I think it would still be worth discussing; like Xiaodi said it's not related to James' original thread-starter.

I agree with this in principle but would not want to see it become a slippery slope back into extremely long access control discussions.

As I've said elsewhere, I too agree with this in principle. I agree with Jordan that the current state of things is justifiable but the alternative would be somewhat superior, agree that in a vacuum this very narrow and specific discussion might be warranted, and agree also that this could be a very slippery slide down a very steep slope.

Same here. It’s the only grudge I have left with the current access control situation. I remember Doug Gregor and John McCall discussing this during the last access control proposal. And I wouldn’t mind having a very narrow discussion about only this.

I organize my types into extensions for each conformance and for each access control. I can currently implicitly apply public or fileprivate to all members of an extension but I have no way of doing the same for private. That’s why I think it should be fixed.

This will break a bunch of code because `private extension` has always meant `fileprivate extension`. Even Swift 3 had this same behavior. Lowering the access level of the extension members will hide a bunch of code that was visible to the file.

169 was not a breaking change but this “fix” would have made it a breaking change. I doubt 169 would had been accepted if it was a breaking change. I don’t think it’s worth it.

https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md

(I maintain that the current model does not include a special case; it simply means the 'private' is resolved at the level of the extension rather than the level of its members. But that isn't what people expect and it's not as useful.)

I agree that changing the behavior of all access modifiers on extensions is out of scope. (I also agree that it is a bad idea. Sorry, James, but wanting 'pubic' here indicates that your mental model of extensions does not match what Swift is actually doing, and that could get you into trouble.)

Jordan

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VladimirS · October 6, 2017, 2:10pm

I appreciate the enthusiasm but this is not a bug. This was a deliberate change in swift 3 to make `private extension` usable. If this was a bug then during swift 3 we should have disallowed `private extension` and only allowed `fileprivate extension` but that is not what happened. `private extension` has worked the same since swift 1. I’ve always used `private extension` when I want to add methods to String or other build in types.

It’s not a bug, but its unfortunate the behaviour wasn’t changed at the same time as SE-0169, and it now is very inconsistent. I also don’t have to rehash previous discussions, but if a Core Team member (Chris) is okay with going ahead with this, perhaps we should consider it.

This could have not been part of 169 because it would've required to lower the visibility of the private extension modifier.

“No migration will be necessary as this proposal merely broadens the visibility of|private|.”

There was a corner case mentioned when dealing with functions with the same name and that was understandable.

private extension is consistent to the way the private scope rules work. The word private is explicit at the top level because extensions can only be declared at top level. Top level private is always fileprivate. The inconsistency is that we have 1 scope ALC and the rest are not. An explicit declaration should always take precedence when declaring something like an access level override.

FWIW, I can't agree with this. 'private extension' is a real point of additional confusion for access levels in Swift.
Extension *by itself* has no access level, we only can specify the *default* (and the top most) access level for inner methods.
I.e. 'private' access modifier for extension has not the same meaning as 'private' func/type/variable at file scope.
(Yes, I also believe we should disallow 'private' keyword at file level and allow it only for extensions, so 'fileprivate' should be used explicitly if one needs this. At least warning should be raised. This is the *root* of the problem we discuss now. But unfortunately I don't expect this could be supported.)
The latter is 'direct' access level for the func/type/variable and here we apply the standard rule for scoped private, so 'private' for file scope --> 'fileprivate'.

The former means 'the default(and top most) modifier that will be auto-inserted by compiler for all nested methods in extension'. This relatively simple rule should not be complicated by additional rule as ", but if it is private extension, result access level will be fileprivate, you can't have extensions with private methods"

And, as was already said, this inconsistency leads to *relaxed* access level, which can lead to bugs. If one expects 'private extension' means 'fileprivate extension' - compiler will show(with error) that this assumption is wrong just after the first attempt to access methods from outside of the extended type.
But if one expects true 'private' access level - the methods from private extension could be called from any other code in the same file(by mistake, or because code was written a long time ago, or by another developer) and this clearly could produce complex bugs.

Also, isn't it a strange code below:

private extension MyType {
   func foo() {}
   private bar() {}
   fileprivate baz() {} // note that "usually" fileprivate is 'wider' access level
}

but it has *currently* a sense - 'foo' is fileprivate, and 'bar' is 'true' private.
Yes, currently we have a warning about 'baz': "warning: declaring a fileprivate instance method in a private extension", but then we have a question "Why?", as private at top level == fileprivate. and this does not produce any warnings:
fileprivate extension MyType {
fileprivate func foo() {}
}

Even more, someone can think "why we need 'private' declaration in private extension, probably this is a mistake i.e. unnecessary duplication of code, I'll refactor this and delete this explicit 'private' because extension is already private' and so will open doors for future problems.

So I do believe we really need to remove that ugly inconsistency and make Swift better to write, understand and support the code.

Vladimir.

···

On 05.10.2017 20:52, Jose Cheyo Jimenez via swift-evolution wrote:

On Oct 5, 2017, at 4:32 AM, David Hart <david@hartbit.com <mailto:david@hartbit.com>> wrote:

On 5 Oct 2017, at 07:34, Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org >>> <mailto:swift-evolution@swift.org>> wrote:

private is different because it is scoped so because of that it is also different when dealing with extensions. Top level private is always the same as fileprivate thanks to its scoped nature.

Making private the scope ACL was a mistake but that ship has sailed and so has this one imo.

On Oct 4, 2017, at 10:05 PM, Tony Allevato <tony.allevato@gmail.com <mailto:tony.allevato@gmail.com>> wrote:

Trust me, I'm the last person who wants to rehash access levels in Swift again. But that's not what's happening here, IMO, and fixing bugs is not just "a change for the sake of changing."

The current behavior of "private extension" is *incorrect*, because it's entirely inconsistent with how access levels on extensions are documented to behave and it's inconsistent with how other access levels apply to extensions.

Can anyone think of a reason—other than "it's too late to change it"—why "private extension" and "fileprivate extension" should behave the same, and why "X extension { decl }" should be identical to "extension { X decl }" for all X *except* "private"?

Yes, it's absolutely unfortunate that this oversight was not addressed when the other access level changes were made. But we shouldn't have to live with bugs in the language because we're afraid of some unknown amount of churn among code that is already written incorrectly. Nor is fixing this bug declaring open season on other, unrelated access level debates. Do you have data that shows that the amount of code broken because it's using "private" when it really should be saying "fileprivate" is high enough that we should just leave the bug there?

On Wed, Oct 4, 2017 at 9:51 PM Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org >>>> <mailto:swift-evolution@swift.org>> wrote:

    There was a high bar for breaking changes in swift 4 and is even higher for swift 5. se-110 was approved and
    implemented on the premises that it was not a big change but it was breaking code so it got reverted. Sure the
    migrator was making this easier but the result was a usability regression. I think this is a change just for the
    sake of changing. This will cause unnecessary churn. Let’s leave ACLs alone for the next few versions of swift
    unless we have a way better system.

    https://lists.swift.org/pipermail/swift-evolution-announce/2017-June/000386.html

    On Oct 4, 2017, at 8:47 PM, BJ Homer <bjhomer@gmail.com <mailto:bjhomer@gmail.com>> wrote:

    It certainly could break *some* code. But it only breaks code written by an author who wrote ‘private
    extension’ knowing that ‘fileprivate extension’ was also an option, but still intended it to be shared with the
    whole file. (If that code was from Swift 2, it would have already been migrated to ‘fileprivate extension’ by
    the 2->3 migrator.)

    So existing code that says ‘private extension’ was written in a Swift 3 or 4 era when ‘fileprivate’ was an
    option. If the goal was specifically to share it with the whole file, it seems likely that most authors would
    have used ‘fileprivate extension’ instead of ‘private extension’, as that better communicates the intention.
    Regardless, though, we could check against the Swift source compatibility test suite to see how widespread that is.

    Regardless, I think this change makes Swift a better language, and I’m in favor of it.

    -BJ

    On Oct 4, 2017, at 9:10 PM, Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org >>>>> <mailto:swift-evolution@swift.org>> wrote:

    On Oct 2, 2017, at 9:59 PM, David Hart via swift-evolution <swift-evolution@swift.org >>>>>> <mailto:swift-evolution@swift.org>> wrote:

    On 3 Oct 2017, at 05:12, Xiaodi Wu via swift-evolution <swift-evolution@swift.org >>>>>>> <mailto:swift-evolution@swift.org>> wrote:

    On Mon, Oct 2, 2017 at 9:16 PM, Matthew Johnson via swift-evolution<swift-evolution@swift.org >>>>>>>> <mailto:swift-evolution@swift.org>>wrote:

        Sent from my iPad

        On Oct 2, 2017, at 7:33 PM, Jordan Rose via swift-evolution <swift-evolution@swift.org >>>>>>>> <mailto:swift-evolution@swift.org>> wrote:

        On Oct 2, 2017, at 03:25, Vladimir.S via swift-evolution <swift-evolution@swift.org >>>>>>>>>> <mailto:swift-evolution@swift.org>> wrote:

        On 01.10.2017 1:18, Chris Lattner wrote:

        On Sep 29, 2017, at 10:42 AM, Xiaodi Wu via swift-evolution <swift-evolution@swift.org >>>>>>>>>>>> <mailto:swift-evolution@swift.org>> wrote:

        Vladimir, I agree with you on that change, but it’s a separate topic from this one.

        Tony is absolutely correct that this topic has already been discussed. It is a deliberate design
        decision that public types do not automatically expose members without explicit access modifiers;
        this has been brought up on this list, and it is clearly not in scope for discussion as no new
        insight can arise this late in the game. The inconsistency with public extensions was brought up,
        the proposed solution was to remove modifiers for extensions, but this proposal was rejected. So,
        the final design is what we have.

        Agreed. The core team would only consider a refinement or change to access control if there were
        something actively broken that mattered for ABI stability.

        So we have to live with *protected* extension inconsistency for very long time just because core team
        don't want to even discuss _this particular_ inconsistency(when access level in *private extension*
        must be private, not fileprivate)?

        Yes, we decided that access level for extension will mean a default and top most access level for
        nested methods, OK. But even in this rule, which already differ from access modifiers for types, we
        have another one special case for 'private extension'.

        Don't you think this is not normal situation and actually there IMO can't be any reason to keep this
        bug-producing inconsistency in Swift? (especially given Swift 5 seems like is a last moment to fix this)

        I hate to say it but I'm inclined to agree with Vladimir on this. "private extension" has a useful
        meaning now distinct from "fileprivate extension", and it was an oversight that SE-0169
        <https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md> didn't
        include a fix here. On this/very narrow, very specific/access control issue I think it would still be
        worth discussing; like Xiaodi said it's not related to James' original thread-starter.

        I agree with this in principle but would not want to see it become a slippery slope back into extremely
        long access control discussions.

    As I've said elsewhere, I too agree with this in principle. I agree with Jordan that the current state of
    things is justifiable but the alternative would be somewhat superior, agree that in a vacuum this very
    narrow and specific discussion might be warranted, and agree also that this could be a very slippery slide
    down a very steep slope.

    Same here. It’s the only grudge I have left with the current access control situation. I remember Doug Gregor
    and John McCall discussing this during the last access control proposal. And I wouldn’t mind having a very
    narrow discussion about only this.

    I organize my types into extensions for each conformance and for each access control. I can currently
    implicitly apply public or fileprivate to all members of an extension but I have no way of doing the same for
    private. That’s why I think it should be fixed.

    This will break a bunch of code because `private extension` has_always_meant `fileprivate extension`.Even
    Swift 3 had this same behavior. Lowering the access level of the extension members will hide a bunch of code
    that was visible to the file.

    169 was not a breaking change but this “fix” would have made it a breaking change. I doubt 169 would had been
    accepted if it was a breaking change. I don’t think it’s worth it.

    https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md

        (I maintain that the current model does/not/ include a special case; it simply means the 'private' is
        resolved at the level of the extension rather than the level of its members. But that isn't what people
        expect and it's not as useful.)

        I agree that changing the behavior of/all/ access modifiers on extensions is out of scope. (I also
        agree that it is a bad idea. Sorry, James, but wanting 'pubic' here indicates that your mental model of
        extensions does not match what Swift is actually doing, and that could get you into trouble.)

        Jordan

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masters3d · October 6, 2017, 5:16pm

I appreciate the enthusiasm but this is not a bug. This was a deliberate change in swift 3 to make `private extension` usable. If this was a bug then during swift 3 we should have disallowed `private extension` and only allowed `fileprivate extension` but that is not what happened. `private extension` has worked the same since swift 1. I’ve always used `private extension` when I want to add methods to String or other build in types.

It’s not a bug, but its unfortunate the behaviour wasn’t changed at the same time as SE-0169, and it now is very inconsistent. I also don’t have to rehash previous discussions, but if a Core Team member (Chris) is okay with going ahead with this, perhaps we should consider it.

This could have not been part of 169 because it would've required to lower the visibility of the private extension modifier.
“No migration will be necessary as this proposal merely broadens the visibility of|private|.”
There was a corner case mentioned when dealing with functions with the same name and that was understandable.
private extension is consistent to the way the private scope rules work. The word private is explicit at the top level because extensions can only be declared at top level. Top level private is always fileprivate. The inconsistency is that we have 1 scope ALC and the rest are not. An explicit declaration should always take precedence when declaring something like an access level override.

FWIW, I can't agree with this. 'private extension' is a real point of additional confusion for access levels in Swift.
Extension *by itself* has no access level, we only can specify the *default* (and the top most) access level for inner methods.
I.e. 'private' access modifier for extension has not the same meaning as 'private' func/type/variable at file scope.
(Yes, I also believe we should disallow 'private' keyword at file level and allow it only for extensions, so 'fileprivate' should be used explicitly if one needs this. At least warning should be raised. This is the *root* of the problem we discuss now. But unfortunately I don't expect this could be supported.)

Wouldn't that just add a special rule to extensions?

The latter is 'direct' access level for the func/type/variable and here we apply the standard rule for scoped private, so 'private' for file scope --> 'fileprivate'.

The former means 'the default(and top most) modifier that will be auto-inserted by compiler for all nested methods in extension'. This relatively simple rule should not be complicated by additional rule as ", but if it is private extension, result access level will be fileprivate, you can't have extensions with private methods”

Private as it exist in swift now is the scope access control label. The compiler does not insert the modifier without having to first compute what access control level would be applied to the members of the extension. Doing it the other way would be counterintuitive for an scope access label. In my code base I disallow top level fileprivate because private top level is fileprivate. This is a matter of taste and a linter here would help like a mentioned up thread.

And, as was already said, this inconsistency leads to *relaxed* access level, which can lead to bugs. If one expects 'private extension' means 'fileprivate extension' - compiler will show(with error) that this assumption is wrong just after the first attempt to access methods from outside of the extended type.
But if one expects true 'private' access level - the methods from private extension could be called from any other code in the same file(by mistake, or because code was written a long time ago, or by another developer) and this clearly could produce complex bugs.

Also, isn't it a strange code below:

private extension MyType {
func foo() {}
private bar() {}
fileprivate baz() {} // note that "usually" fileprivate is 'wider' access level
}

This is also strange too

fileprivate class MyType {
open func foo(){} // Is this open or fileprivate?
public func bar(){}
}

open class MyType2 {
}

open extension MyType2 { // Error: Extensions cannot use 'open' as their default access; use 'public'
func baz(){}
}

but it has *currently* a sense - 'foo' is fileprivate, and 'bar' is 'true' private.
Yes, currently we have a warning about 'baz': "warning: declaring a fileprivate instance method in a private extension", but then we have a question "Why?", as private at top level == fileprivate. and this does not produce any warnings:
fileprivate extension MyType {
fileprivate func foo() {}
}

Even more, someone can think "why we need 'private' declaration in private extension, probably this is a mistake i.e. unnecessary duplication of code, I'll refactor this and delete this explicit 'private' because extension is already private' and so will open doors for future problems.

So I do believe we really need to remove that ugly inconsistency and make Swift better to write, understand and support the code.

This is matter of taste. For example I think fileprivate is ugly and having both private and fileprivate makes the code hard to understand.

···

On Oct 6, 2017, at 7:10 AM, Vladimir.S <svabox@gmail.com> wrote:
On 05.10.2017 20:52, Jose Cheyo Jimenez via swift-evolution wrote:

On Oct 5, 2017, at 4:32 AM, David Hart <david@hartbit.com <mailto:david@hartbit.com>> wrote:

On 5 Oct 2017, at 07:34, Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

Vladimir.

private is different because it is scoped so because of that it is also different when dealing with extensions. Top level private is always the same as fileprivate thanks to its scoped nature.

Making private the scope ACL was a mistake but that ship has sailed and so has this one imo.

On Oct 4, 2017, at 10:05 PM, Tony Allevato <tony.allevato@gmail.com <mailto:tony.allevato@gmail.com>> wrote:

Trust me, I'm the last person who wants to rehash access levels in Swift again. But that's not what's happening here, IMO, and fixing bugs is not just "a change for the sake of changing."

The current behavior of "private extension" is *incorrect*, because it's entirely inconsistent with how access levels on extensions are documented to behave and it's inconsistent with how other access levels apply to extensions.

Can anyone think of a reason—other than "it's too late to change it"—why "private extension" and "fileprivate extension" should behave the same, and why "X extension { decl }" should be identical to "extension { X decl }" for all X *except* "private"?

Yes, it's absolutely unfortunate that this oversight was not addressed when the other access level changes were made. But we shouldn't have to live with bugs in the language because we're afraid of some unknown amount of churn among code that is already written incorrectly. Nor is fixing this bug declaring open season on other, unrelated access level debates. Do you have data that shows that the amount of code broken because it's using "private" when it really should be saying "fileprivate" is high enough that we should just leave the bug there?

On Wed, Oct 4, 2017 at 9:51 PM Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

   There was a high bar for breaking changes in swift 4 and is even higher for swift 5. se-110 was approved and
   implemented on the premises that it was not a big change but it was breaking code so it got reverted. Sure the
   migrator was making this easier but the result was a usability regression. I think this is a change just for the
   sake of changing. This will cause unnecessary churn. Let’s leave ACLs alone for the next few versions of swift
   unless we have a way better system.

   https://lists.swift.org/pipermail/swift-evolution-announce/2017-June/000386.html

   On Oct 4, 2017, at 8:47 PM, BJ Homer <bjhomer@gmail.com <mailto:bjhomer@gmail.com>> wrote:

   It certainly could break *some* code. But it only breaks code written by an author who wrote ‘private
   extension’ knowing that ‘fileprivate extension’ was also an option, but still intended it to be shared with the
   whole file. (If that code was from Swift 2, it would have already been migrated to ‘fileprivate extension’ by
   the 2->3 migrator.)

   So existing code that says ‘private extension’ was written in a Swift 3 or 4 era when ‘fileprivate’ was an
   option. If the goal was specifically to share it with the whole file, it seems likely that most authors would
   have used ‘fileprivate extension’ instead of ‘private extension’, as that better communicates the intention.
   Regardless, though, we could check against the Swift source compatibility test suite to see how widespread that is.

   Regardless, I think this change makes Swift a better language, and I’m in favor of it.

   -BJ

   On Oct 4, 2017, at 9:10 PM, Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org >>>>>> <mailto:swift-evolution@swift.org>> wrote:

   On Oct 2, 2017, at 9:59 PM, David Hart via swift-evolution <swift-evolution@swift.org >>>>>>> <mailto:swift-evolution@swift.org>> wrote:

   On 3 Oct 2017, at 05:12, Xiaodi Wu via swift-evolution <swift-evolution@swift.org >>>>>>>> <mailto:swift-evolution@swift.org>> wrote:

   On Mon, Oct 2, 2017 at 9:16 PM, Matthew Johnson via swift-evolution<swift-evolution@swift.org >>>>>>>>> <mailto:swift-evolution@swift.org>>wrote:

       Sent from my iPad

       On Oct 2, 2017, at 7:33 PM, Jordan Rose via swift-evolution <swift-evolution@swift.org >>>>>>>>> <mailto:swift-evolution@swift.org>> wrote:

       On Oct 2, 2017, at 03:25, Vladimir.S via swift-evolution <swift-evolution@swift.org >>>>>>>>>>> <mailto:swift-evolution@swift.org>> wrote:

       On 01.10.2017 1:18, Chris Lattner wrote:

       On Sep 29, 2017, at 10:42 AM, Xiaodi Wu via swift-evolution <swift-evolution@swift.org >>>>>>>>>>>>> <mailto:swift-evolution@swift.org>> wrote:

       Vladimir, I agree with you on that change, but it’s a separate topic from this one.

       Tony is absolutely correct that this topic has already been discussed. It is a deliberate design
       decision that public types do not automatically expose members without explicit access modifiers;
       this has been brought up on this list, and it is clearly not in scope for discussion as no new
       insight can arise this late in the game. The inconsistency with public extensions was brought up,
       the proposed solution was to remove modifiers for extensions, but this proposal was rejected. So,
       the final design is what we have.

       Agreed. The core team would only consider a refinement or change to access control if there were
       something actively broken that mattered for ABI stability.

       So we have to live with *protected* extension inconsistency for very long time just because core team
       don't want to even discuss _this particular_ inconsistency(when access level in *private extension*
       must be private, not fileprivate)?

       Yes, we decided that access level for extension will mean a default and top most access level for
       nested methods, OK. But even in this rule, which already differ from access modifiers for types, we
       have another one special case for 'private extension'.

       Don't you think this is not normal situation and actually there IMO can't be any reason to keep this
       bug-producing inconsistency in Swift? (especially given Swift 5 seems like is a last moment to fix this)

       I hate to say it but I'm inclined to agree with Vladimir on this. "private extension" has a useful
       meaning now distinct from "fileprivate extension", and it was an oversight that SE-0169
       <https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md> didn't
       include a fix here. On this/very narrow, very specific/access control issue I think it would still be
       worth discussing; like Xiaodi said it's not related to James' original thread-starter.

       I agree with this in principle but would not want to see it become a slippery slope back into extremely
       long access control discussions.

   As I've said elsewhere, I too agree with this in principle. I agree with Jordan that the current state of
   things is justifiable but the alternative would be somewhat superior, agree that in a vacuum this very
   narrow and specific discussion might be warranted, and agree also that this could be a very slippery slide
   down a very steep slope.

   Same here. It’s the only grudge I have left with the current access control situation. I remember Doug Gregor
   and John McCall discussing this during the last access control proposal. And I wouldn’t mind having a very
   narrow discussion about only this.

   I organize my types into extensions for each conformance and for each access control. I can currently
   implicitly apply public or fileprivate to all members of an extension but I have no way of doing the same for
   private. That’s why I think it should be fixed.

   This will break a bunch of code because `private extension` has_always_meant `fileprivate extension`.Even
   Swift 3 had this same behavior. Lowering the access level of the extension members will hide a bunch of code
   that was visible to the file.

   169 was not a breaking change but this “fix” would have made it a breaking change. I doubt 169 would had been
   accepted if it was a breaking change. I don’t think it’s worth it.

   https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md

       (I maintain that the current model does/not/ include a special case; it simply means the 'private' is
       resolved at the level of the extension rather than the level of its members. But that isn't what people
       expect and it's not as useful.)

       I agree that changing the behavior of/all/ access modifiers on extensions is out of scope. (I also
       agree that it is a bad idea. Sorry, James, but wanting 'pubic' here indicates that your mental model of
       extensions does not match what Swift is actually doing, and that could get you into trouble.)

       Jordan

       _______________________________________________
       swift-evolution mailing list
       swift-evolution@swift.org <mailto:swift-evolution@swift.org>
       https://lists.swift.org/mailman/listinfo/swift-evolution

       _______________________________________________
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   https://lists.swift.org/mailman/listinfo/swift-evolution

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   swift-evolution mailing list
   swift-evolution@swift.org <mailto:swift-evolution@swift.org>
   https://lists.swift.org/mailman/listinfo/swift-evolution

   _______________________________________________
   swift-evolution mailing list
   swift-evolution@swift.org <mailto:swift-evolution@swift.org>
   https://lists.swift.org/mailman/listinfo/swift-evolution

   _______________________________________________
   swift-evolution mailing list
   swift-evolution@swift.org <mailto:swift-evolution@swift.org>
   https://lists.swift.org/mailman/listinfo/swift-evolution

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https://lists.swift.org/mailman/listinfo/swift-evolution

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swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

xwu · October 6, 2017, 5:27pm

These exceed the confines of the narrow discussion we are trying to have
here about private extensions. We are not going to rehash the ugliness of
fileprivate.

···

On Fri, Oct 6, 2017 at 12:16 Jose Cheyo Jimenez via swift-evolution < swift-evolution@swift.org> wrote:

On Oct 6, 2017, at 7:10 AM, Vladimir.S <svabox@gmail.com> wrote:

On 05.10.2017 20:52, Jose Cheyo Jimenez via swift-evolution wrote:

On Oct 5, 2017, at 4:32 AM, David Hart <david@hartbit.com < > mailto:david@hartbit.com <david@hartbit.com>>> wrote:

On 5 Oct 2017, at 07:34, Jose Cheyo Jimenez via swift-evolution < > swift-evolution@swift.org <mailto:swift-evolution@swift.org > <swift-evolution@swift.org>>> wrote:

I appreciate the enthusiasm but this is not a bug. This was a deliberate
change in swift 3 to make `private extension` usable. If this was a bug
then during swift 3 we should have disallowed `private extension` and only
allowed `fileprivate extension` but that is not what happened. `private
extension` has worked the same since swift 1. I’ve always used `private
extension` when I want to add methods to String or other build in types.

It’s not a bug, but its unfortunate the behaviour wasn’t changed at the
same time as SE-0169, and it now is very inconsistent. I also don’t have to
rehash previous discussions, but if a Core Team member (Chris) is okay with
going ahead with this, perhaps we should consider it.

This could have not been part of 169 because it would've required to lower
the visibility of the private extension modifier.
“No migration will be necessary as this proposal merely broadens the
visibility of|private|.”
There was a corner case mentioned when dealing with functions with the
same name and that was understandable.
private extension is consistent to the way the private scope rules work.
The word private is explicit at the top level because extensions can only
be declared at top level. Top level private is always fileprivate. The
inconsistency is that we have 1 scope ALC and the rest are not. An explicit
declaration should always take precedence when declaring something like an
access level override.

FWIW, I can't agree with this. 'private extension' is a real point of
additional confusion for access levels in Swift.
Extension *by itself* has no access level, we only can specify the
*default* (and the top most) access level for inner methods.
I.e. 'private' access modifier for extension has not the same meaning as
'private' func/type/variable at file scope.
(Yes, I also believe we should disallow 'private' keyword at file level
and allow it only for extensions, so 'fileprivate' should be used
explicitly if one needs this. At least warning should be raised. This is
the *root* of the problem we discuss now. But unfortunately I don't expect
this could be supported.)

Wouldn't that just add a *special* rule to extensions?

The latter is 'direct' access level for the func/type/variable and here we
apply the standard rule for scoped private, so 'private' for file scope -->
'fileprivate'.

The former means 'the default(and top most) modifier that will be
auto-inserted by compiler for all nested methods in extension'. This
relatively simple rule should not be complicated by additional rule as ",
but if it is private extension, result access level will be fileprivate,
you can't have extensions with private methods”

Private as it exist in swift now is the scope access control label. The
compiler does not insert the modifier without having to first compute what
access control level would be applied to the members of the extension.
Doing it the other way would be counterintuitive for an scope access label.
In my code base I disallow top level fileprivate because private top level
is fileprivate. This is a matter of taste and a linter here would help like
a mentioned up thread.

And, as was already said, this inconsistency leads to *relaxed* access
level, which can lead to bugs. If one expects 'private extension' means
'fileprivate extension' - compiler will show(with error) that this
assumption is wrong just after the first attempt to access methods from
outside of the extended type.
But if one expects true 'private' access level - the methods from private
extension could be called from any other code in the same file(by mistake,
or because code was written a long time ago, or by another developer) and
this clearly could produce complex bugs.

Also, isn't it a strange code below:

private extension MyType {
func foo() {}
private bar() {}
fileprivate baz() {} // note that "usually" fileprivate is 'wider' access
level
}

This is also strange too

fileprivate class MyType {
  open func foo(){} // Is this open or fileprivate?
  public func bar(){}
}

open class MyType2 {
}

open extension MyType2 { // Error: Extensions cannot use 'open' as their
default access; use 'public'
    func baz(){}
}

but it has *currently* a sense - 'foo' is fileprivate, and 'bar' is 'true'
private.
Yes, currently we have a warning about 'baz': "warning: declaring a
fileprivate instance method in a private extension", but then we have a
question "Why?", as private at top level == fileprivate. and this does not
produce any warnings:
fileprivate extension MyType {
fileprivate func foo() {}
}

Even more, someone can think "why we need 'private' declaration in private
extension, probably this is a mistake i.e. unnecessary duplication of code,
I'll refactor this and delete this explicit 'private' because extension is
already private' and so will open doors for future problems.

So I do believe we really need to remove that ugly inconsistency and make
Swift better to write, understand and support the code.

This is matter of taste. For example I think fileprivate is ugly and
having both private and fileprivate makes the code hard to understand.

Vladimir.

private is different because it is scoped so because of that it is also
different when dealing with extensions. Top level private is always the
same as fileprivate thanks to its scoped nature.

Making private the scope ACL was a mistake but that ship has sailed and so
has this one imo.

On Oct 4, 2017, at 10:05 PM, Tony Allevato <tony.allevato@gmail.com < > mailto:tony.allevato@gmail.com <tony.allevato@gmail.com>>> wrote:

Trust me, I'm the last person who wants to rehash access levels in Swift
again. But that's not what's happening here, IMO, and fixing bugs is not
just "a change for the sake of changing."

The current behavior of "private extension" is *incorrect*, because it's
entirely inconsistent with how access levels on extensions are documented
to behave and it's inconsistent with how other access levels apply to
extensions.

Can anyone think of a reason—other than "it's too late to change it"—why
"private extension" and "fileprivate extension" should behave the same, and
why "X extension { decl }" should be identical to "extension { X decl }"
for all X *except* "private"?

Yes, it's absolutely unfortunate that this oversight was not addressed
when the other access level changes were made. But we shouldn't have to
live with bugs in the language because we're afraid of some unknown amount
of churn among code that is already written incorrectly. Nor is fixing this
bug declaring open season on other, unrelated access level debates. Do you
have data that shows that the amount of code broken because it's using
"private" when it really should be saying "fileprivate" is high enough that
we should just leave the bug there?

On Wed, Oct 4, 2017 at 9:51 PM Jose Cheyo Jimenez via swift-evolution < > swift-evolution@swift.org <mailto:swift-evolution@swift.org > <swift-evolution@swift.org>>> wrote:

   There was a high bar for breaking changes in swift 4 and is even higher
for swift 5. se-110 was approved and
   implemented on the premises that it was not a big change but it was
breaking code so it got reverted. Sure the
   migrator was making this easier but the result was a usability
regression. I think this is a change just for the
   sake of changing. This will cause unnecessary churn. Let’s leave ACLs
alone for the next few versions of swift
   unless we have a way better system.

https://lists.swift.org/pipermail/swift-evolution-announce/2017-June/000386.html

   On Oct 4, 2017, at 8:47 PM, BJ Homer <bjhomer@gmail.com < > mailto:bjhomer@gmail.com <bjhomer@gmail.com>>> wrote:

   It certainly could break *some* code. But it only breaks code written
by an author who wrote ‘private
   extension’ knowing that ‘fileprivate extension’ was also an option, but
still intended it to be shared with the
   whole file. (If that code was from Swift 2, it would have already been
migrated to ‘fileprivate extension’ by
   the 2->3 migrator.)

   So existing code that says ‘private extension’ was written in a Swift 3
or 4 era when ‘fileprivate’ was an
   option. If the goal was specifically to share it with the whole file,
it seems likely that most authors would
   have used ‘fileprivate extension’ instead of ‘private extension’, as
that better communicates the intention.
   Regardless, though, we could check against the Swift source
compatibility test suite to see how widespread that is.

   Regardless, I think this change makes Swift a better language, and I’m
in favor of it.

   -BJ

   On Oct 4, 2017, at 9:10 PM, Jose Cheyo Jimenez via swift-evolution < > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> wrote:

   On Oct 2, 2017, at 9:59 PM, David Hart via swift-evolution < > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> wrote:

   On 3 Oct 2017, at 05:12, Xiaodi Wu via swift-evolution < > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> wrote:

   On Mon, Oct 2, 2017 at 9:16 PM, Matthew Johnson via swift-evolution< > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>>wrote:

       Sent from my iPad

       On Oct 2, 2017, at 7:33 PM, Jordan Rose via swift-evolution < > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> > wrote:

       On Oct 2, 2017, at 03:25, Vladimir.S via swift-evolution < > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> > wrote:

       On 01.10.2017 1:18, Chris Lattner wrote:

       On Sep 29, 2017, at 10:42 AM, Xiaodi Wu via swift-evolution < > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> > wrote:

       Vladimir, I agree with you on that change, but it’s a separate
topic from this one.

       Tony is absolutely correct that this topic has already been
discussed. It is a deliberate design
       decision that public types do not automatically expose members
without explicit access modifiers;
       this has been brought up on this list, and it is clearly not in
scope for discussion as no new
       insight can arise this late in the game. The inconsistency with
public extensions was brought up,
       the proposed solution was to remove modifiers for extensions, but
this proposal was rejected. So,
       the final design is what we have.

       Agreed. The core team would only consider a refinement or change
to access control if there were
       something actively broken that mattered for ABI stability.

       So we have to live with *protected* extension inconsistency for
very long time just because core team
       don't want to even discuss _this particular_ inconsistency(when
access level in *private extension*
       must be private, not fileprivate)?

       Yes, we decided that access level for extension will mean a default
and top most access level for
       nested methods, OK. But even in this rule, which already differ
from access modifiers for types, we
       have another one special case for 'private extension'.

       Don't you think this is not normal situation and actually there IMO
can't be any reason to keep this
       bug-producing inconsistency in Swift? (especially given Swift 5
seems like is a last moment to fix this)

       I hate to say it but I'm inclined to agree with Vladimir on this.
"private extension" has a useful
       meaning now distinct from "fileprivate extension", and it was an
oversight that SE-0169
       <
https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md>
didn't
       include a fix here. On this/very narrow, very specific/access
control issue I think it would still be
       worth discussing; like Xiaodi said it's not related to James'
original thread-starter.

       I agree with this in principle but would not want to see it become
a slippery slope back into extremely
       long access control discussions.

   As I've said elsewhere, I too agree with this in principle. I agree
with Jordan that the current state of
   things is justifiable but the alternative would be somewhat superior,
agree that in a vacuum this very
   narrow and specific discussion might be warranted, and agree also that
this could be a very slippery slide
   down a very steep slope.

   Same here. It’s the only grudge I have left with the current access
control situation. I remember Doug Gregor
   and John McCall discussing this during the last access control
proposal. And I wouldn’t mind having a very
   narrow discussion about only this.

   I organize my types into extensions for each conformance and for each
access control. I can currently
   implicitly apply public or fileprivate to all members of an extension
but I have no way of doing the same for
   private. That’s why I think it should be fixed.

   This will break a bunch of code because `private extension`
has_always_meant `fileprivate extension`.Even
   Swift 3 had this same behavior. Lowering the access level of the
extension members will hide a bunch of code
   that was visible to the file.

   169 was not a breaking change but this “fix” would have made it a
breaking change. I doubt 169 would had been
   accepted if it was a breaking change. I don’t think it’s worth it.

https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md

       (I maintain that the current model does/not/ include a special
case; it simply means the 'private' is
       resolved at the level of the extension rather than the level of its
members. But that isn't what people
       expect and it's not as useful.)

       I agree that changing the behavior of/all/ access modifiers on
extensions is out of scope. (I also
       agree that it is a bad idea. Sorry, James, but wanting 'pubic' here
indicates that your mental model of
       extensions does not match what Swift is actually doing, and that
could get you into trouble.)

       Jordan

       _______________________________________________
       swift-evolution mailing list
       swift-evolution@swift.org <mailto:swift-evolution@swift.org
<swift-evolution@swift.org>>
       https://lists.swift.org/mailman/listinfo/swift-evolution

       _______________________________________________
       swift-evolution mailing list
       swift-evolution@swift.org <mailto:swift-evolution@swift.org
<swift-evolution@swift.org>>
       https://lists.swift.org/mailman/listinfo/swift-evolution

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<swift-evolution@swift.org>>
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allevato · October 6, 2017, 6:07pm

I appreciate the enthusiasm but this is not a bug. This was a deliberate
change in swift 3 to make `private extension` usable. If this was a bug
then during swift 3 we should have disallowed `private extension` and only
allowed `fileprivate extension` but that is not what happened. `private
extension` has worked the same since swift 1. I’ve always used `private
extension` when I want to add methods to String or other build in types.

It’s not a bug, but its unfortunate the behaviour wasn’t changed at the
same time as SE-0169, and it now is very inconsistent. I also don’t have to
rehash previous discussions, but if a Core Team member (Chris) is okay with
going ahead with this, perhaps we should consider it.

This could have not been part of 169 because it would've required to lower
the visibility of the private extension modifier.
“No migration will be necessary as this proposal merely broadens the
visibility of|private|.”
There was a corner case mentioned when dealing with functions with the
same name and that was understandable.
private extension is consistent to the way the private scope rules work.
The word private is explicit at the top level because extensions can only
be declared at top level. Top level private is always fileprivate. The
inconsistency is that we have 1 scope ALC and the rest are not. An explicit
declaration should always take precedence when declaring something like an
access level override.

FWIW, I can't agree with this. 'private extension' is a real point of
additional confusion for access levels in Swift.
Extension *by itself* has no access level, we only can specify the
*default* (and the top most) access level for inner methods.
I.e. 'private' access modifier for extension has not the same meaning as
'private' func/type/variable at file scope.
(Yes, I also believe we should disallow 'private' keyword at file level
and allow it only for extensions, so 'fileprivate' should be used
explicitly if one needs this. At least warning should be raised. This is
the *root* of the problem we discuss now. But unfortunately I don't expect
this could be supported.)

Wouldn't that just add a *special* rule to extensions?

The latter is 'direct' access level for the func/type/variable and here we
apply the standard rule for scoped private, so 'private' for file scope -->
'fileprivate'.

The former means 'the default(and top most) modifier that will be
auto-inserted by compiler for all nested methods in extension'. This
relatively simple rule should not be complicated by additional rule as ",
but if it is private extension, result access level will be fileprivate,
you can't have extensions with private methods”

Private as it exist in swift now is the scope access control label. The
compiler does not insert the modifier without having to first compute what
access control level would be applied to the members of the extension.
Doing it the other way would be counterintuitive for an scope access label.
In my code base I disallow top level fileprivate because private top level
is fileprivate. This is a matter of taste and a linter here would help like
a mentioned up thread.

This is the sticking point, which is why there are two possible
interpretations of "private extension":

Choice 1) Attach-then-evaluate. "ACL extension { ... }" is a syntactic
shortcut for "extension { ACL ... }". Under that definition, the ACL is
evaluated as if it were attached to each declaration, so "private
extension" would expand to "private" in front of each decl.

Choice 2) Evaluate-then-attach. "ACL extension { ... }" is evaluated such
that "ACL" takes on the meaning based on its scope; since it's equivalent
to "fileprivate" there, that is what is attached to each declaration inside
the extension.

The phrasing in the official Swift language guide doesn't specifically
state it, but I think most readers would interpret the following as #1:

"Alternatively, you can mark an extension with an explicit access-level
modifier (for example, `private extension`) to set a new default access
level for all members defined within the extension."

I personally find that choice to be the clearer interpretation of the rule,
because it's based entirely on what words are in the source file and not
about how they interact in special edge cases.

I also think it's hard to rationalize "private extension" working like #2
because compared to #1, it's both duplicative ("private extension" and
"fileprivate extension" are awkwardly the same) _and_ it is strictly less
flexible (there is _no_ way using that syntax to define an extension whose
members are private, which is an inconsistent hole in the language).

···

On Fri, Oct 6, 2017 at 10:16 AM Jose Cheyo Jimenez via swift-evolution < swift-evolution@swift.org> wrote:

On Oct 6, 2017, at 7:10 AM, Vladimir.S <svabox@gmail.com> wrote:
On 05.10.2017 20:52, Jose Cheyo Jimenez via swift-evolution wrote:
On Oct 5, 2017, at 4:32 AM, David Hart <david@hartbit.com < > mailto:david@hartbit.com <david@hartbit.com>>> wrote:
On 5 Oct 2017, at 07:34, Jose Cheyo Jimenez via swift-evolution < > swift-evolution@swift.org <mailto:swift-evolution@swift.org > <swift-evolution@swift.org>>> wrote:

And, as was already said, this inconsistency leads to *relaxed* access
level, which can lead to bugs. If one expects 'private extension' means
'fileprivate extension' - compiler will show(with error) that this
assumption is wrong just after the first attempt to access methods from
outside of the extended type.
But if one expects true 'private' access level - the methods from private
extension could be called from any other code in the same file(by mistake,
or because code was written a long time ago, or by another developer) and
this clearly could produce complex bugs.

Also, isn't it a strange code below:

private extension MyType {
func foo() {}
private bar() {}
fileprivate baz() {} // note that "usually" fileprivate is 'wider' access
level
}

This is also strange too

fileprivate class MyType {
  open func foo(){} // Is this open or fileprivate?
  public func bar(){}
}

open class MyType2 {
}

open extension MyType2 { // Error: Extensions cannot use 'open' as their
default access; use 'public'
    func baz(){}
}

but it has *currently* a sense - 'foo' is fileprivate, and 'bar' is 'true'
private.
Yes, currently we have a warning about 'baz': "warning: declaring a
fileprivate instance method in a private extension", but then we have a
question "Why?", as private at top level == fileprivate. and this does not
produce any warnings:
fileprivate extension MyType {
fileprivate func foo() {}
}

Even more, someone can think "why we need 'private' declaration in private
extension, probably this is a mistake i.e. unnecessary duplication of code,
I'll refactor this and delete this explicit 'private' because extension is
already private' and so will open doors for future problems.

So I do believe we really need to remove that ugly inconsistency and make
Swift better to write, understand and support the code.

This is matter of taste. For example I think fileprivate is ugly and
having both private and fileprivate makes the code hard to understand.

Vladimir.

private is different because it is scoped so because of that it is also
different when dealing with extensions. Top level private is always the
same as fileprivate thanks to its scoped nature.

Making private the scope ACL was a mistake but that ship has sailed and so
has this one imo.

On Oct 4, 2017, at 10:05 PM, Tony Allevato <tony.allevato@gmail.com < > mailto:tony.allevato@gmail.com <tony.allevato@gmail.com>>> wrote:

Trust me, I'm the last person who wants to rehash access levels in Swift
again. But that's not what's happening here, IMO, and fixing bugs is not
just "a change for the sake of changing."

The current behavior of "private extension" is *incorrect*, because it's
entirely inconsistent with how access levels on extensions are documented
to behave and it's inconsistent with how other access levels apply to
extensions.

Can anyone think of a reason—other than "it's too late to change it"—why
"private extension" and "fileprivate extension" should behave the same, and
why "X extension { decl }" should be identical to "extension { X decl }"
for all X *except* "private"?

Yes, it's absolutely unfortunate that this oversight was not addressed
when the other access level changes were made. But we shouldn't have to
live with bugs in the language because we're afraid of some unknown amount
of churn among code that is already written incorrectly. Nor is fixing this
bug declaring open season on other, unrelated access level debates. Do you
have data that shows that the amount of code broken because it's using
"private" when it really should be saying "fileprivate" is high enough that
we should just leave the bug there?

On Wed, Oct 4, 2017 at 9:51 PM Jose Cheyo Jimenez via swift-evolution < > swift-evolution@swift.org <mailto:swift-evolution@swift.org > <swift-evolution@swift.org>>> wrote:

   There was a high bar for breaking changes in swift 4 and is even higher
for swift 5. se-110 was approved and
   implemented on the premises that it was not a big change but it was
breaking code so it got reverted. Sure the
   migrator was making this easier but the result was a usability
regression. I think this is a change just for the
   sake of changing. This will cause unnecessary churn. Let’s leave ACLs
alone for the next few versions of swift
   unless we have a way better system.

https://lists.swift.org/pipermail/swift-evolution-announce/2017-June/000386.html

   On Oct 4, 2017, at 8:47 PM, BJ Homer <bjhomer@gmail.com < > mailto:bjhomer@gmail.com <bjhomer@gmail.com>>> wrote:

   It certainly could break *some* code. But it only breaks code written
by an author who wrote ‘private
   extension’ knowing that ‘fileprivate extension’ was also an option, but
still intended it to be shared with the
   whole file. (If that code was from Swift 2, it would have already been
migrated to ‘fileprivate extension’ by
   the 2->3 migrator.)

   So existing code that says ‘private extension’ was written in a Swift 3
or 4 era when ‘fileprivate’ was an
   option. If the goal was specifically to share it with the whole file,
it seems likely that most authors would
   have used ‘fileprivate extension’ instead of ‘private extension’, as
that better communicates the intention.
   Regardless, though, we could check against the Swift source
compatibility test suite to see how widespread that is.

   Regardless, I think this change makes Swift a better language, and I’m
in favor of it.

   -BJ

   On Oct 4, 2017, at 9:10 PM, Jose Cheyo Jimenez via swift-evolution < > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> wrote:

   On Oct 2, 2017, at 9:59 PM, David Hart via swift-evolution < > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> wrote:

   On 3 Oct 2017, at 05:12, Xiaodi Wu via swift-evolution < > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> wrote:

   On Mon, Oct 2, 2017 at 9:16 PM, Matthew Johnson via swift-evolution< > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>>wrote:

       Sent from my iPad

       On Oct 2, 2017, at 7:33 PM, Jordan Rose via swift-evolution < > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> > wrote:

       On Oct 2, 2017, at 03:25, Vladimir.S via swift-evolution < > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> > wrote:

       On 01.10.2017 1:18, Chris Lattner wrote:

       On Sep 29, 2017, at 10:42 AM, Xiaodi Wu via swift-evolution < > swift-evolution@swift.org > <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> > wrote:

       Vladimir, I agree with you on that change, but it’s a separate
topic from this one.

       Tony is absolutely correct that this topic has already been
discussed. It is a deliberate design
       decision that public types do not automatically expose members
without explicit access modifiers;
       this has been brought up on this list, and it is clearly not in
scope for discussion as no new
       insight can arise this late in the game. The inconsistency with
public extensions was brought up,
       the proposed solution was to remove modifiers for extensions, but
this proposal was rejected. So,
       the final design is what we have.

       Agreed. The core team would only consider a refinement or change
to access control if there were
       something actively broken that mattered for ABI stability.

       So we have to live with *protected* extension inconsistency for
very long time just because core team
       don't want to even discuss _this particular_ inconsistency(when
access level in *private extension*
       must be private, not fileprivate)?

       Yes, we decided that access level for extension will mean a default
and top most access level for
       nested methods, OK. But even in this rule, which already differ
from access modifiers for types, we
       have another one special case for 'private extension'.

       Don't you think this is not normal situation and actually there IMO
can't be any reason to keep this
       bug-producing inconsistency in Swift? (especially given Swift 5
seems like is a last moment to fix this)

       I hate to say it but I'm inclined to agree with Vladimir on this.
"private extension" has a useful
       meaning now distinct from "fileprivate extension", and it was an
oversight that SE-0169
       <
https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md>
didn't
       include a fix here. On this/very narrow, very specific/access
control issue I think it would still be
       worth discussing; like Xiaodi said it's not related to James'
original thread-starter.

       I agree with this in principle but would not want to see it become
a slippery slope back into extremely
       long access control discussions.

   As I've said elsewhere, I too agree with this in principle. I agree
with Jordan that the current state of
   things is justifiable but the alternative would be somewhat superior,
agree that in a vacuum this very
   narrow and specific discussion might be warranted, and agree also that
this could be a very slippery slide
   down a very steep slope.

   Same here. It’s the only grudge I have left with the current access
control situation. I remember Doug Gregor
   and John McCall discussing this during the last access control
proposal. And I wouldn’t mind having a very
   narrow discussion about only this.

   I organize my types into extensions for each conformance and for each
access control. I can currently
   implicitly apply public or fileprivate to all members of an extension
but I have no way of doing the same for
   private. That’s why I think it should be fixed.

   This will break a bunch of code because `private extension`
has_always_meant `fileprivate extension`.Even
   Swift 3 had this same behavior. Lowering the access level of the
extension members will hide a bunch of code
   that was visible to the file.

   169 was not a breaking change but this “fix” would have made it a
breaking change. I doubt 169 would had been
   accepted if it was a breaking change. I don’t think it’s worth it.

https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md

       (I maintain that the current model does/not/ include a special
case; it simply means the 'private' is
       resolved at the level of the extension rather than the level of its
members. But that isn't what people
       expect and it's not as useful.)

       I agree that changing the behavior of/all/ access modifiers on
extensions is out of scope. (I also
       agree that it is a bad idea. Sorry, James, but wanting 'pubic' here
indicates that your mental model of
       extensions does not match what Swift is actually doing, and that
could get you into trouble.)

       Jordan

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masters3d · October 7, 2017, 2:07am

I appreciate the enthusiasm but this is not a bug. This was a deliberate change in swift 3 to make `private extension` usable. If this was a bug then during swift 3 we should have disallowed `private extension` and only allowed `fileprivate extension` but that is not what happened. `private extension` has worked the same since swift 1. I’ve always used `private extension` when I want to add methods to String or other build in types.

It’s not a bug, but its unfortunate the behaviour wasn’t changed at the same time as SE-0169, and it now is very inconsistent. I also don’t have to rehash previous discussions, but if a Core Team member (Chris) is okay with going ahead with this, perhaps we should consider it.

This could have not been part of 169 because it would've required to lower the visibility of the private extension modifier.
“No migration will be necessary as this proposal merely broadens the visibility of|private|.”
There was a corner case mentioned when dealing with functions with the same name and that was understandable.
private extension is consistent to the way the private scope rules work. The word private is explicit at the top level because extensions can only be declared at top level. Top level private is always fileprivate. The inconsistency is that we have 1 scope ALC and the rest are not. An explicit declaration should always take precedence when declaring something like an access level override.

FWIW, I can't agree with this. 'private extension' is a real point of additional confusion for access levels in Swift.
Extension *by itself* has no access level, we only can specify the *default* (and the top most) access level for inner methods.
I.e. 'private' access modifier for extension has not the same meaning as 'private' func/type/variable at file scope.
(Yes, I also believe we should disallow 'private' keyword at file level and allow it only for extensions, so 'fileprivate' should be used explicitly if one needs this. At least warning should be raised. This is the *root* of the problem we discuss now. But unfortunately I don't expect this could be supported.)

Wouldn't that just add a special rule to extensions?

The latter is 'direct' access level for the func/type/variable and here we apply the standard rule for scoped private, so 'private' for file scope --> 'fileprivate'.

The former means 'the default(and top most) modifier that will be auto-inserted by compiler for all nested methods in extension'. This relatively simple rule should not be complicated by additional rule as ", but if it is private extension, result access level will be fileprivate, you can't have extensions with private methods”

Private as it exist in swift now is the scope access control label. The compiler does not insert the modifier without having to first compute what access control level would be applied to the members of the extension. Doing it the other way would be counterintuitive for an scope access label. In my code base I disallow top level fileprivate because private top level is fileprivate. This is a matter of taste and a linter here would help like a mentioned up thread.

This is the sticking point, which is why there are two possible interpretations of "private extension":

Choice 1) Attach-then-evaluate. "ACL extension { ... }" is a syntactic shortcut for "extension { ACL ... }". Under that definition, the ACL is evaluated as if it were attached to each declaration, so "private extension" would expand to "private" in front of each decl.

Choice 2) Evaluate-then-attach. "ACL extension { ... }" is evaluated such that "ACL" takes on the meaning based on its scope; since it's equivalent to "fileprivate" there, that is what is attached to each declaration inside the extension.

Yep. This is the issue. Nice summary!

The phrasing in the official Swift language guide doesn't specifically state it, but I think most readers would interpret the following as #1:

"Alternatively, you can mark an extension with an explicit access-level modifier (for example, `private extension`) to set a new default access level for all members defined within the extension."

I personally find that choice to be the clearer interpretation of the rule, because it's based entirely on what words are in the source file and not about how they interact in special edge cases.

Documentation is hard to keep in sync.
https://github.com/apple/swift-evolution/blob/master/proposals/0025-scoped-access-level.md#complications-with-private-types

I also think it's hard to rationalize "private extension" working like #2 because compared to #1, it's both duplicative ("private extension" and "fileprivate extension" are awkwardly the same) _and_ it is strictly less flexible (there is _no_ way using that syntax to define an extension whose members are private, which is an inconsistent hole in the language).

This compiles on an Xcode 9 playground. SE-0025 doesn't only affect extensions.
``MyClass.myFunc()` looks like (Choice 2) to me. Same as `private extension MyClass2`.

private class MyClass {
    static func myFunc(){
        print(“Acts likes fileprivate")
    }
}

private class MyClass2 {
}

private extension MyClass2{
    static func myFunc2(){
       print("Same as MyClass.myFunc")
    }
}

MyClass.myFunc() // Acts likes fileprivate
MyClass2.myFunc2() // Same as MyClass.myFunc

···

On Oct 6, 2017, at 11:07 AM, Tony Allevato <tony.allevato@gmail.com> wrote:
On Fri, Oct 6, 2017 at 10:16 AM Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On Oct 6, 2017, at 7:10 AM, Vladimir.S <svabox@gmail.com <mailto:svabox@gmail.com>> wrote:
On 05.10.2017 20:52, Jose Cheyo Jimenez via swift-evolution wrote:

On Oct 5, 2017, at 4:32 AM, David Hart <david@hartbit.com <mailto:david@hartbit.com><mailto:david@hartbit.com <mailto:david@hartbit.com>>> wrote:

On 5 Oct 2017, at 07:34, Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org>>> wrote:

And, as was already said, this inconsistency leads to *relaxed* access level, which can lead to bugs. If one expects 'private extension' means 'fileprivate extension' - compiler will show(with error) that this assumption is wrong just after the first attempt to access methods from outside of the extended type.
But if one expects true 'private' access level - the methods from private extension could be called from any other code in the same file(by mistake, or because code was written a long time ago, or by another developer) and this clearly could produce complex bugs.

Also, isn't it a strange code below:

private extension MyType {
func foo() {}
private bar() {}
fileprivate baz() {} // note that "usually" fileprivate is 'wider' access level
}

This is also strange too

fileprivate class MyType {
  open func foo(){} // Is this open or fileprivate?
  public func bar(){}
}

open class MyType2 {
}

open extension MyType2 { // Error: Extensions cannot use 'open' as their default access; use 'public'
    func baz(){}
}

but it has *currently* a sense - 'foo' is fileprivate, and 'bar' is 'true' private.
Yes, currently we have a warning about 'baz': "warning: declaring a fileprivate instance method in a private extension", but then we have a question "Why?", as private at top level == fileprivate. and this does not produce any warnings:
fileprivate extension MyType {
  fileprivate func foo() {}
}

Even more, someone can think "why we need 'private' declaration in private extension, probably this is a mistake i.e. unnecessary duplication of code, I'll refactor this and delete this explicit 'private' because extension is already private' and so will open doors for future problems.

So I do believe we really need to remove that ugly inconsistency and make Swift better to write, understand and support the code.

This is matter of taste. For example I think fileprivate is ugly and having both private and fileprivate makes the code hard to understand.

Vladimir.

private is different because it is scoped so because of that it is also different when dealing with extensions. Top level private is always the same as fileprivate thanks to its scoped nature.

Making private the scope ACL was a mistake but that ship has sailed and so has this one imo.

On Oct 4, 2017, at 10:05 PM, Tony Allevato <tony.allevato@gmail.com <mailto:tony.allevato@gmail.com> <mailto:tony.allevato@gmail.com <mailto:tony.allevato@gmail.com>>> wrote:

Trust me, I'm the last person who wants to rehash access levels in Swift again. But that's not what's happening here, IMO, and fixing bugs is not just "a change for the sake of changing."

The current behavior of "private extension" is *incorrect*, because it's entirely inconsistent with how access levels on extensions are documented to behave and it's inconsistent with how other access levels apply to extensions.

Can anyone think of a reason—other than "it's too late to change it"—why "private extension" and "fileprivate extension" should behave the same, and why "X extension { decl }" should be identical to "extension { X decl }" for all X *except* "private"?

Yes, it's absolutely unfortunate that this oversight was not addressed when the other access level changes were made. But we shouldn't have to live with bugs in the language because we're afraid of some unknown amount of churn among code that is already written incorrectly. Nor is fixing this bug declaring open season on other, unrelated access level debates. Do you have data that shows that the amount of code broken because it's using "private" when it really should be saying "fileprivate" is high enough that we should just leave the bug there?

On Wed, Oct 4, 2017 at 9:51 PM Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org>>> wrote:

   There was a high bar for breaking changes in swift 4 and is even higher for swift 5. se-110 was approved and
   implemented on the premises that it was not a big change but it was breaking code so it got reverted. Sure the
   migrator was making this easier but the result was a usability regression. I think this is a change just for the
   sake of changing. This will cause unnecessary churn. Let’s leave ACLs alone for the next few versions of swift
   unless we have a way better system.

   https://lists.swift.org/pipermail/swift-evolution-announce/2017-June/000386.html

   On Oct 4, 2017, at 8:47 PM, BJ Homer <bjhomer@gmail.com <mailto:bjhomer@gmail.com><mailto:bjhomer@gmail.com <mailto:bjhomer@gmail.com>>> wrote:

   It certainly could break *some* code. But it only breaks code written by an author who wrote ‘private
   extension’ knowing that ‘fileprivate extension’ was also an option, but still intended it to be shared with the
   whole file. (If that code was from Swift 2, it would have already been migrated to ‘fileprivate extension’ by
   the 2->3 migrator.)

   So existing code that says ‘private extension’ was written in a Swift 3 or 4 era when ‘fileprivate’ was an
   option. If the goal was specifically to share it with the whole file, it seems likely that most authors would
   have used ‘fileprivate extension’ instead of ‘private extension’, as that better communicates the intention.
   Regardless, though, we could check against the Swift source compatibility test suite to see how widespread that is.

   Regardless, I think this change makes Swift a better language, and I’m in favor of it.

   -BJ

   On Oct 4, 2017, at 9:10 PM, Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>>>>>> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org>>> wrote:

   On Oct 2, 2017, at 9:59 PM, David Hart via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>>>>>>> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org>>> wrote:

   On 3 Oct 2017, at 05:12, Xiaodi Wu via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>>>>>>>> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org>>> wrote:

   On Mon, Oct 2, 2017 at 9:16 PM, Matthew Johnson via swift-evolution<swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>>>>>>>>> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org>>>wrote:

       Sent from my iPad

       On Oct 2, 2017, at 7:33 PM, Jordan Rose via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>>>>>>>>> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org>>> wrote:

       On Oct 2, 2017, at 03:25, Vladimir.S via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>>>>>>>>>>> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org>>> wrote:

       On 01.10.2017 1:18, Chris Lattner wrote:

       On Sep 29, 2017, at 10:42 AM, Xiaodi Wu via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org> >>>>>>>>>>>>>> <mailto:swift-evolution@swift.org <mailto:swift-evolution@swift.org>>> wrote:

       Vladimir, I agree with you on that change, but it’s a separate topic from this one.

       Tony is absolutely correct that this topic has already been discussed. It is a deliberate design
       decision that public types do not automatically expose members without explicit access modifiers;
       this has been brought up on this list, and it is clearly not in scope for discussion as no new
       insight can arise this late in the game. The inconsistency with public extensions was brought up,
       the proposed solution was to remove modifiers for extensions, but this proposal was rejected. So,
       the final design is what we have.

       Agreed. The core team would only consider a refinement or change to access control if there were
       something actively broken that mattered for ABI stability.

       So we have to live with *protected* extension inconsistency for very long time just because core team
       don't want to even discuss _this particular_ inconsistency(when access level in *private extension*
       must be private, not fileprivate)?

       Yes, we decided that access level for extension will mean a default and top most access level for
       nested methods, OK. But even in this rule, which already differ from access modifiers for types, we
       have another one special case for 'private extension'.

       Don't you think this is not normal situation and actually there IMO can't be any reason to keep this
       bug-producing inconsistency in Swift? (especially given Swift 5 seems like is a last moment to fix this)

       I hate to say it but I'm inclined to agree with Vladimir on this. "private extension" has a useful
       meaning now distinct from "fileprivate extension", and it was an oversight that SE-0169
       <https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md> didn't
       include a fix here. On this/very narrow, very specific/access control issue I think it would still be
       worth discussing; like Xiaodi said it's not related to James' original thread-starter.

       I agree with this in principle but would not want to see it become a slippery slope back into extremely
       long access control discussions.

   As I've said elsewhere, I too agree with this in principle. I agree with Jordan that the current state of
   things is justifiable but the alternative would be somewhat superior, agree that in a vacuum this very
   narrow and specific discussion might be warranted, and agree also that this could be a very slippery slide
   down a very steep slope.

   Same here. It’s the only grudge I have left with the current access control situation. I remember Doug Gregor
   and John McCall discussing this during the last access control proposal. And I wouldn’t mind having a very
   narrow discussion about only this.

   I organize my types into extensions for each conformance and for each access control. I can currently
   implicitly apply public or fileprivate to all members of an extension but I have no way of doing the same for
   private. That’s why I think it should be fixed.

   This will break a bunch of code because `private extension` has_always_meant `fileprivate extension`.Even
   Swift 3 had this same behavior. Lowering the access level of the extension members will hide a bunch of code
   that was visible to the file.

   169 was not a breaking change but this “fix” would have made it a breaking change. I doubt 169 would had been
   accepted if it was a breaking change. I don’t think it’s worth it.

   https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md

       (I maintain that the current model does/not/ include a special case; it simply means the 'private' is
       resolved at the level of the extension rather than the level of its members. But that isn't what people
       expect and it's not as useful.)

       I agree that changing the behavior of/all/ access modifiers on extensions is out of scope. (I also
       agree that it is a bad idea. Sorry, James, but wanting 'pubic' here indicates that your mental model of
       extensions does not match what Swift is actually doing, and that could get you into trouble.)

       Jordan

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allevato · October 7, 2017, 3:01am

I appreciate the enthusiasm but this is not a bug. This was a deliberate
change in swift 3 to make `private extension` usable. If this was a bug
then during swift 3 we should have disallowed `private extension` and only
allowed `fileprivate extension` but that is not what happened. `private
extension` has worked the same since swift 1. I’ve always used `private
extension` when I want to add methods to String or other build in types.

It’s not a bug, but its unfortunate the behaviour wasn’t changed at the
same time as SE-0169, and it now is very inconsistent. I also don’t have to
rehash previous discussions, but if a Core Team member (Chris) is okay with
going ahead with this, perhaps we should consider it.

This could have not been part of 169 because it would've required to
lower the visibility of the private extension modifier.
“No migration will be necessary as this proposal merely broadens the
visibility of|private|.”
There was a corner case mentioned when dealing with functions with the
same name and that was understandable.
private extension is consistent to the way the private scope rules work.
The word private is explicit at the top level because extensions can only
be declared at top level. Top level private is always fileprivate. The
inconsistency is that we have 1 scope ALC and the rest are not. An explicit
declaration should always take precedence when declaring something like an
access level override.

FWIW, I can't agree with this. 'private extension' is a real point of
additional confusion for access levels in Swift.
Extension *by itself* has no access level, we only can specify the
*default* (and the top most) access level for inner methods.
I.e. 'private' access modifier for extension has not the same meaning as
'private' func/type/variable at file scope.
(Yes, I also believe we should disallow 'private' keyword at file level
and allow it only for extensions, so 'fileprivate' should be used
explicitly if one needs this. At least warning should be raised. This is
the *root* of the problem we discuss now. But unfortunately I don't expect
this could be supported.)

Wouldn't that just add a *special* rule to extensions?

The latter is 'direct' access level for the func/type/variable and here
we apply the standard rule for scoped private, so 'private' for file scope
--> 'fileprivate'.

The former means 'the default(and top most) modifier that will be
auto-inserted by compiler for all nested methods in extension'. This
relatively simple rule should not be complicated by additional rule as ",
but if it is private extension, result access level will be fileprivate,
you can't have extensions with private methods”

Private as it exist in swift now is the scope access control label. The
compiler does not insert the modifier without having to first compute what
access control level would be applied to the members of the extension.
Doing it the other way would be counterintuitive for an scope access label.
In my code base I disallow top level fileprivate because private top level
is fileprivate. This is a matter of taste and a linter here would help like
a mentioned up thread.

This is the sticking point, which is why there are two possible
interpretations of "private extension":

Choice 1) Attach-then-evaluate. "ACL extension { ... }" is a syntactic
shortcut for "extension { ACL ... }". Under that definition, the ACL is
evaluated as if it were attached to each declaration, so "private
extension" would expand to "private" in front of each decl.

Choice 2) Evaluate-then-attach. "ACL extension { ... }" is evaluated such
that "ACL" takes on the meaning based on its scope; since it's equivalent
to "fileprivate" there, that is what is attached to each declaration inside
the extension.

Yep. This is the issue. Nice summary!

The phrasing in the official Swift language guide doesn't specifically
state it, but I think most readers would interpret the following as #1:

"Alternatively, you can mark an extension with an explicit access-level
modifier (for example, `private extension`) to set a new default access
level for all members defined within the extension."

I personally find that choice to be the clearer interpretation of the
rule, because it's based entirely on what words are in the source file and
not about how they interact in special edge cases.

Documentation is hard to keep in sync.

https://github.com/apple/swift-evolution/blob/master/proposals/0025-scoped-access-level.md#complications-with-private-types

At the time SE-0025 was accepted, "private extension" would have been
meaningless if it did not mean "fileprivate" because it predated the
SE-0169 behavior extending "private" to extensions in the same file. The
very issue being debated here is whether the oversight that SE-0169 did not
consider extensions—now that "private extension" *could* have a meaningful
use separate from "fileprivate extension"—is something that is worth
correcting.

If the documentation is out-of-date and needs to be updated to list
describe unintuitive special behavior, why not use the opportunity to make
the behavior intuitive and consistent instead?

I also think it's hard to rationalize "private extension" working like #2
because compared to #1, it's both duplicative ("private extension" and
"fileprivate extension" are awkwardly the same) _and_ it is strictly less
flexible (there is _no_ way using that syntax to define an extension whose
members are private, which is an inconsistent hole in the language).

This compiles on an Xcode 9 playground. SE-0025 doesn't only affect
extensions.
``MyClass.myFunc()` looks like (Choice 2) to me. Same as `private
extension MyClass2`.

private class MyClass {
    static func myFunc(){
        print(“Acts likes fileprivate")
    }
}

private class MyClass2 {
}

private extension MyClass2{
    static func myFunc2(){
       print("Same as MyClass.myFunc")
    }
}

MyClass.myFunc() // Acts likes fileprivate
MyClass2.myFunc2() // Same as MyClass.myFunc

This example is somewhat irrelevant to what's being discussed here—it's
purely about SE-0025 behavior rather than, as the original message said,
the extremely narrow specific case of access control for extensions.

···

On Fri, Oct 6, 2017 at 7:07 PM Jose Cheyo Jimenez <cheyo@masters3d.com> wrote:

On Oct 6, 2017, at 11:07 AM, Tony Allevato <tony.allevato@gmail.com> > wrote:
On Fri, Oct 6, 2017 at 10:16 AM Jose Cheyo Jimenez via swift-evolution < > swift-evolution@swift.org> wrote:

On Oct 6, 2017, at 7:10 AM, Vladimir.S <svabox@gmail.com> wrote:
On 05.10.2017 20:52, Jose Cheyo Jimenez via swift-evolution wrote:
On Oct 5, 2017, at 4:32 AM, David Hart <david@hartbit.com< >> mailto:david@hartbit.com <david@hartbit.com>>> wrote:
On 5 Oct 2017, at 07:34, Jose Cheyo Jimenez via swift-evolution < >> swift-evolution@swift.org <mailto:swift-evolution@swift.org >> <swift-evolution@swift.org>>> wrote:

And, as was already said, this inconsistency leads to *relaxed* access
level, which can lead to bugs. If one expects 'private extension' means
'fileprivate extension' - compiler will show(with error) that this
assumption is wrong just after the first attempt to access methods from
outside of the extended type.
But if one expects true 'private' access level - the methods from private
extension could be called from any other code in the same file(by mistake,
or because code was written a long time ago, or by another developer) and
this clearly could produce complex bugs.

Also, isn't it a strange code below:

private extension MyType {
func foo() {}
private bar() {}
fileprivate baz() {} // note that "usually" fileprivate is 'wider'
access level
}

This is also strange too

fileprivate class MyType {
  open func foo(){} // Is this open or fileprivate?
  public func bar(){}
}

open class MyType2 {
}

open extension MyType2 { // Error: Extensions cannot use 'open' as their
default access; use 'public'
    func baz(){}
}

but it has *currently* a sense - 'foo' is fileprivate, and 'bar' is
'true' private.
Yes, currently we have a warning about 'baz': "warning: declaring a
fileprivate instance method in a private extension", but then we have a
question "Why?", as private at top level == fileprivate. and this does not
produce any warnings:
fileprivate extension MyType {
fileprivate func foo() {}
}

Even more, someone can think "why we need 'private' declaration in
private extension, probably this is a mistake i.e. unnecessary duplication
of code, I'll refactor this and delete this explicit 'private' because
extension is already private' and so will open doors for future problems.

So I do believe we really need to remove that ugly inconsistency and make
Swift better to write, understand and support the code.

This is matter of taste. For example I think fileprivate is ugly and
having both private and fileprivate makes the code hard to understand.

Vladimir.

private is different because it is scoped so because of that it is also
different when dealing with extensions. Top level private is always the
same as fileprivate thanks to its scoped nature.

Making private the scope ACL was a mistake but that ship has sailed and
so has this one imo.

On Oct 4, 2017, at 10:05 PM, Tony Allevato <tony.allevato@gmail.com < >> mailto:tony.allevato@gmail.com <tony.allevato@gmail.com>>> wrote:

Trust me, I'm the last person who wants to rehash access levels in Swift
again. But that's not what's happening here, IMO, and fixing bugs is not
just "a change for the sake of changing."

The current behavior of "private extension" is *incorrect*, because it's
entirely inconsistent with how access levels on extensions are documented
to behave and it's inconsistent with how other access levels apply to
extensions.

Can anyone think of a reason—other than "it's too late to change it"—why
"private extension" and "fileprivate extension" should behave the same, and
why "X extension { decl }" should be identical to "extension { X decl }"
for all X *except* "private"?

Yes, it's absolutely unfortunate that this oversight was not addressed
when the other access level changes were made. But we shouldn't have to
live with bugs in the language because we're afraid of some unknown amount
of churn among code that is already written incorrectly. Nor is fixing this
bug declaring open season on other, unrelated access level debates. Do you
have data that shows that the amount of code broken because it's using
"private" when it really should be saying "fileprivate" is high enough that
we should just leave the bug there?

On Wed, Oct 4, 2017 at 9:51 PM Jose Cheyo Jimenez via swift-evolution < >> swift-evolution@swift.org <mailto:swift-evolution@swift.org >> <swift-evolution@swift.org>>> wrote:

   There was a high bar for breaking changes in swift 4 and is even
higher for swift 5. se-110 was approved and
   implemented on the premises that it was not a big change but it was
breaking code so it got reverted. Sure the
   migrator was making this easier but the result was a usability
regression. I think this is a change just for the
   sake of changing. This will cause unnecessary churn. Let’s leave ACLs
alone for the next few versions of swift
   unless we have a way better system.

https://lists.swift.org/pipermail/swift-evolution-announce/2017-June/000386.html

   On Oct 4, 2017, at 8:47 PM, BJ Homer <bjhomer@gmail.com< >> mailto:bjhomer@gmail.com <bjhomer@gmail.com>>> wrote:

   It certainly could break *some* code. But it only breaks code written
by an author who wrote ‘private
   extension’ knowing that ‘fileprivate extension’ was also an option,
but still intended it to be shared with the
   whole file. (If that code was from Swift 2, it would have already been
migrated to ‘fileprivate extension’ by
   the 2->3 migrator.)

   So existing code that says ‘private extension’ was written in a Swift
3 or 4 era when ‘fileprivate’ was an
   option. If the goal was specifically to share it with the whole file,
it seems likely that most authors would
   have used ‘fileprivate extension’ instead of ‘private extension’, as
that better communicates the intention.
   Regardless, though, we could check against the Swift source
compatibility test suite to see how widespread that is.

   Regardless, I think this change makes Swift a better language, and I’m
in favor of it.

   -BJ

   On Oct 4, 2017, at 9:10 PM, Jose Cheyo Jimenez via swift-evolution < >> swift-evolution@swift.org >> <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> wrote:

   On Oct 2, 2017, at 9:59 PM, David Hart via swift-evolution < >> swift-evolution@swift.org >> <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> wrote:

   On 3 Oct 2017, at 05:12, Xiaodi Wu via swift-evolution < >> swift-evolution@swift.org >> <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> wrote:

   On Mon, Oct 2, 2017 at 9:16 PM, Matthew Johnson via swift-evolution< >> swift-evolution@swift.org >> <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>>wrote:

       Sent from my iPad

       On Oct 2, 2017, at 7:33 PM, Jordan Rose via swift-evolution < >> swift-evolution@swift.org >> <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> >> wrote:

       On Oct 2, 2017, at 03:25, Vladimir.S via swift-evolution < >> swift-evolution@swift.org >> <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> >> wrote:

       On 01.10.2017 1:18, Chris Lattner wrote:

       On Sep 29, 2017, at 10:42 AM, Xiaodi Wu via swift-evolution < >> swift-evolution@swift.org >> <mailto:swift-evolution@swift.org <swift-evolution@swift.org>>> >> wrote:

       Vladimir, I agree with you on that change, but it’s a separate
topic from this one.

       Tony is absolutely correct that this topic has already been
discussed. It is a deliberate design
       decision that public types do not automatically expose members
without explicit access modifiers;
       this has been brought up on this list, and it is clearly not in
scope for discussion as no new
       insight can arise this late in the game. The inconsistency with
public extensions was brought up,
       the proposed solution was to remove modifiers for extensions, but
this proposal was rejected. So,
       the final design is what we have.

       Agreed. The core team would only consider a refinement or change
to access control if there were
       something actively broken that mattered for ABI stability.

       So we have to live with *protected* extension inconsistency for
very long time just because core team
       don't want to even discuss _this particular_ inconsistency(when
access level in *private extension*
       must be private, not fileprivate)?

       Yes, we decided that access level for extension will mean a
default and top most access level for
       nested methods, OK. But even in this rule, which already differ
from access modifiers for types, we
       have another one special case for 'private extension'.

       Don't you think this is not normal situation and actually there
IMO can't be any reason to keep this
       bug-producing inconsistency in Swift? (especially given Swift 5
seems like is a last moment to fix this)

       I hate to say it but I'm inclined to agree with Vladimir on this.
"private extension" has a useful
       meaning now distinct from "fileprivate extension", and it was an
oversight that SE-0169
       <
https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md>
didn't
       include a fix here. On this/very narrow, very specific/access
control issue I think it would still be
       worth discussing; like Xiaodi said it's not related to James'
original thread-starter.

       I agree with this in principle but would not want to see it become
a slippery slope back into extremely
       long access control discussions.

   As I've said elsewhere, I too agree with this in principle. I agree
with Jordan that the current state of
   things is justifiable but the alternative would be somewhat superior,
agree that in a vacuum this very
   narrow and specific discussion might be warranted, and agree also that
this could be a very slippery slide
   down a very steep slope.

   Same here. It’s the only grudge I have left with the current access
control situation. I remember Doug Gregor
   and John McCall discussing this during the last access control
proposal. And I wouldn’t mind having a very
   narrow discussion about only this.

   I organize my types into extensions for each conformance and for each
access control. I can currently
   implicitly apply public or fileprivate to all members of an extension
but I have no way of doing the same for
   private. That’s why I think it should be fixed.

   This will break a bunch of code because `private extension`
has_always_meant `fileprivate extension`.Even
   Swift 3 had this same behavior. Lowering the access level of the
extension members will hide a bunch of code
   that was visible to the file.

   169 was not a breaking change but this “fix” would have made it a
breaking change. I doubt 169 would had been
   accepted if it was a breaking change. I don’t think it’s worth it.

https://github.com/apple/swift-evolution/blob/master/proposals/0169-improve-interaction-between-private-declarations-and-extensions.md

       (I maintain that the current model does/not/ include a special
case; it simply means the 'private' is
       resolved at the level of the extension rather than the level of
its members. But that isn't what people
       expect and it's not as useful.)

       I agree that changing the behavior of/all/ access modifiers on
extensions is out of scope. (I also
       agree that it is a bad idea. Sorry, James, but wanting 'pubic'
here indicates that your mental model of
       extensions does not match what Swift is actually doing, and that
could get you into trouble.)

       Jordan

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masters3d · October 7, 2017, 3:44am

Lets say you “fix” the private extension override. Now MyClass2.myFunc2() is not accessible from outside the type.
Wouldn't MyClass2.myFunc2() now be inconsistent with MyClass.myFunc()?
I don’t think you can make a change to one with out causing other inconsistencies. I rest my case.

private class MyClass {
    static func myFunc(){ // This would now act differently from private extensions?
        print("acts like fileprivate now")
    }
}

private class MyClass2 {}

private extension MyClass2{
      static func myFunc2(){
       print("Same as MyClass.myFunc")
    }
}

MyClass.myFunc() // acts like fileprivate
MyClass2.myFunc2() // The proposed change would hide myFunc2
//Error: 'myFunc2' is inaccessible due to 'private' protection level

···

On Oct 6, 2017, at 8:01 PM, Tony Allevato <tony.allevato@gmail.com> wrote:

At the time SE-0025 was accepted, "private extension" would have been meaningless if it did not mean "fileprivate" because it predated the SE-0169 behavior extending "private" to extensions in the same file. The very issue being debated here is whether the oversight that SE-0169 did not consider extensions—now that "private extension" *could* have a meaningful use separate from "fileprivate extension"—is something that is worth correcting.

If the documentation is out-of-date and needs to be updated to list describe unintuitive special behavior, why not use the opportunity to make the behavior intuitive and consistent instead?

allevato · October 7, 2017, 3:58am

At the time SE-0025 was accepted, "private extension" would have been

meaningless if it did not mean "fileprivate" because it predated the
SE-0169 behavior extending "private" to extensions in the same file. The
very issue being debated here is whether the oversight that SE-0169 did not
consider extensions—now that "private extension" *could* have a meaningful
use separate from "fileprivate extension"—is something that is worth
correcting.

If the documentation is out-of-date and needs to be updated to list
describe unintuitive special behavior, why not use the opportunity to make
the behavior intuitive and consistent instead?

Lets say you “fix” the private extension override. Now MyClass2.myFunc2()
is not accessible from outside the type.
Wouldn't MyClass2.myFunc2() now be inconsistent with MyClass.myFunc()?
I don’t think you can make a change to one with out causing other
inconsistencies. I rest my case.

No, because a class is a concrete "thing" whose access level which—while
providing an upper bound for access levels of its defaulting members—is
otherwise independent of the access level of its members.

Extensions, on the other hand, aren't a concrete thing of their own. The
access level on an extension exists *solely* as a shortcut to specify the
upper bound for its defaulting members that are injected into the main type.

What happens in your example if you replace "private" with "public"? Then
myFunc has internal access but myFunc2 is public. So the "inconsistency"
you're pointing out between access inherited from a type and access
inherited from an extension already exists—they're apples and oranges.

That's why access levels of classes/structs/other types aren't relevant
examples here—extensions treat access levels fundamentally differently.

···

On Fri, Oct 6, 2017 at 8:45 PM Jose Cheyo Jimenez <cheyo@masters3d.com> wrote:

On Oct 6, 2017, at 8:01 PM, Tony Allevato <tony.allevato@gmail.com> wrote:

private class MyClass {
    static func myFunc(){ // This would now act differently from private
extensions?
        print("acts like fileprivate now")
    }
}

private class MyClass2 {}

private extension MyClass2{
      static func myFunc2(){
       print("Same as MyClass.myFunc")
    }
}

MyClass.myFunc() // acts like fileprivate
MyClass2.myFunc2() // The proposed change would hide myFunc2
             //Error: 'myFunc2' is inaccessible due to 'private'
protection level

masters3d · October 7, 2017, 4:29am

At the time SE-0025 was accepted, "private extension" would have been meaningless if it did not mean "fileprivate" because it predated the SE-0169 behavior extending "private" to extensions in the same file. The very issue being debated here is whether the oversight that SE-0169 did not consider extensions—now that "private extension" *could* have a meaningful use separate from "fileprivate extension"—is something that is worth correcting.

If the documentation is out-of-date and needs to be updated to list describe unintuitive special behavior, why not use the opportunity to make the behavior intuitive and consistent instead?

Lets say you “fix” the private extension override. Now MyClass2.myFunc2() is not accessible from outside the type.
Wouldn't MyClass2.myFunc2() now be inconsistent with MyClass.myFunc()?
I don’t think you can make a change to one with out causing other inconsistencies. I rest my case.

No, because a class is a concrete "thing" whose access level which—while providing an upper bound for access levels of its defaulting members—is otherwise independent of the access level of its members.

Extensions, on the other hand, aren't a concrete thing of their own. The access level on an extension exists *solely* as a shortcut to specify the upper bound for its defaulting members that are injected into the main type.

What happens in your example if you replace "private" with "public"? Then myFunc has internal access but myFunc2 is public. So the "inconsistency" you're pointing out between access inherited from a type and access inherited from an extension already exists—they're apples and oranges.

That's why access levels of classes/structs/other types aren't relevant examples here—extensions treat access levels fundamentally differently.

Sure. Extensions apply a default upper bound and types can lower the upper bound of the default internal members. The upper bound on the below example is the same for both when dealing with top level private.

Extensions should resolve their upper bound accessibility where the ‘private’ appears explicitly and this now happens to be the same for both types and extensions regardless of how they are enforced.

···

On Oct 6, 2017, at 8:58 PM, Tony Allevato <tony.allevato@gmail.com> wrote:
On Fri, Oct 6, 2017 at 8:45 PM Jose Cheyo Jimenez <cheyo@masters3d.com <mailto:cheyo@masters3d.com>> wrote:

On Oct 6, 2017, at 8:01 PM, Tony Allevato <tony.allevato@gmail.com <mailto:tony.allevato@gmail.com>> wrote:

private class MyClass {
    static func myFunc(){ // This would now act differently from private extensions?
        print("acts like fileprivate now")
    }
}

private class MyClass2 {}

private extension MyClass2{
      static func myFunc2(){
       print("Same as MyClass.myFunc")
    }
}

MyClass.myFunc() // acts like fileprivate
MyClass2.myFunc2() // The proposed change would hide myFunc2
             //Error: 'myFunc2' is inaccessible due to 'private' protection level

allevato · October 7, 2017, 4:35am

At the time SE-0025 was accepted, "private extension" would have been

meaningless if it did not mean "fileprivate" because it predated the
SE-0169 behavior extending "private" to extensions in the same file. The
very issue being debated here is whether the oversight that SE-0169 did not
consider extensions—now that "private extension" *could* have a meaningful
use separate from "fileprivate extension"—is something that is worth
correcting.

If the documentation is out-of-date and needs to be updated to list
describe unintuitive special behavior, why not use the opportunity to make
the behavior intuitive and consistent instead?

Lets say you “fix” the private extension override. Now MyClass2.myFunc2()
is not accessible from outside the type.
Wouldn't MyClass2.myFunc2() now be inconsistent with MyClass.myFunc()?
I don’t think you can make a change to one with out causing other
inconsistencies. I rest my case.

No, because a class is a concrete "thing" whose access level which—while
providing an upper bound for access levels of its defaulting members—is
otherwise independent of the access level of its members.

Extensions, on the other hand, aren't a concrete thing of their own. The
access level on an extension exists *solely* as a shortcut to specify the
upper bound for its defaulting members that are injected into the main type.

What happens in your example if you replace "private" with "public"? Then
myFunc has internal access but myFunc2 is public. So the "inconsistency"
you're pointing out between access inherited from a type and access
inherited from an extension already exists—they're apples and oranges.

That's why access levels of classes/structs/other types aren't relevant
examples here—extensions treat access levels fundamentally differently.

Sure. Extensions apply a default upper bound and types can lower the upper
bound of the default internal members. The upper bound on the below example
is the same for both when dealing with top level private.

Extensions should resolve their upper bound accessibility where the
‘private’ appears explicitly and this now happens to be the same for both
types and extensions regardless of how they are enforced.

But *why* do you think that should be? You're stating what the current
situation is and you say that it "should" be that way, but why should we
accept that status quo instead of making "private extension" more useful
for people who use "private" in the sense introduced by SE-0169, when the
argument for consistency can honestly be argued either way (the two options
I wrote a few messages up)?

···

On Fri, Oct 6, 2017 at 9:29 PM Jose Cheyo Jimenez <cheyo@masters3d.com> wrote:

On Oct 6, 2017, at 8:58 PM, Tony Allevato <tony.allevato@gmail.com> wrote:
On Fri, Oct 6, 2017 at 8:45 PM Jose Cheyo Jimenez <cheyo@masters3d.com> > wrote:

On Oct 6, 2017, at 8:01 PM, Tony Allevato <tony.allevato@gmail.com> >> wrote:

private class MyClass {
    static func myFunc(){ // This would now act differently from private
extensions?
        print("acts like fileprivate now")
    }
}

private class MyClass2 {}

private extension MyClass2{
      static func myFunc2(){
       print("Same as MyClass.myFunc")
    }
}

MyClass.myFunc() // acts like fileprivate
MyClass2.myFunc2() // The proposed change would hide myFunc2
             //Error: 'myFunc2' is inaccessible due to 'private'
protection level

masters3d · October 7, 2017, 5:06am

At the time SE-0025 was accepted, "private extension" would have been meaningless if it did not mean "fileprivate" because it predated the SE-0169 behavior extending "private" to extensions in the same file. The very issue being debated here is whether the oversight that SE-0169 did not consider extensions—now that "private extension" *could* have a meaningful use separate from "fileprivate extension"—is something that is worth correcting.

If the documentation is out-of-date and needs to be updated to list describe unintuitive special behavior, why not use the opportunity to make the behavior intuitive and consistent instead?

Lets say you “fix” the private extension override. Now MyClass2.myFunc2() is not accessible from outside the type.
Wouldn't MyClass2.myFunc2() now be inconsistent with MyClass.myFunc()?
I don’t think you can make a change to one with out causing other inconsistencies. I rest my case.

No, because a class is a concrete "thing" whose access level which—while providing an upper bound for access levels of its defaulting members—is otherwise independent of the access level of its members.

Extensions, on the other hand, aren't a concrete thing of their own. The access level on an extension exists *solely* as a shortcut to specify the upper bound for its defaulting members that are injected into the main type.

What happens in your example if you replace "private" with "public"? Then myFunc has internal access but myFunc2 is public. So the "inconsistency" you're pointing out between access inherited from a type and access inherited from an extension already exists—they're apples and oranges.

That's why access levels of classes/structs/other types aren't relevant examples here—extensions treat access levels fundamentally differently.

Sure. Extensions apply a default upper bound and types can lower the upper bound of the default internal members. The upper bound on the below example is the same for both when dealing with top level private.

Extensions should resolve their upper bound accessibility where the ‘private’ appears explicitly and this now happens to be the same for both types and extensions regardless of how they are enforced.

But *why* do you think that should be? You're stating what the current situation is and you say that it "should" be that way, but why should we accept that status quo instead of making "private extension" more useful for people who use "private" in the sense introduced by SE-0169, when the argument for consistency can honestly be argued either way (the two options I wrote a few messages up)?

Oh Because I believe that lowering the scope of “private extension” would undermine the spirit of 169. 169 was a compromise after 159 was rejected. 169 was meant to make fileprivate less common and thus more meaningful when it occurs in source. Where 169 was meant to relax the rules, the proposed “fix” would force people who now use “private extension” to use “fileprivate extension” thus making fileprivate more common. In other words, 169 was about relaxing rules and not about tightening down the rules or allowing “true” private to be applied as a default ACL extension.

“scoped" `private extension` can’t be archived now in the same way that ‘open extension’ is not allowed. The lowest and highest ACL are not able to be applied as default extension modifiers and this makes sense to me.

There is no solution that will make everyone happy: maintaining the status quo makes “fileprivate” too common and therefore not meaningful when it occurs in source; removing or diluting scope-level access control (as in SE-0159 <https://github.com/apple/swift-evolution/blob/master/proposals/0159-fix-private-access-levels.md> and this proposal)
https://lists.swift.org/pipermail/swift-evolution-announce/2017-April/000357.html

···

On Oct 6, 2017, at 9:35 PM, Tony Allevato <tony.allevato@gmail.com> wrote:
On Fri, Oct 6, 2017 at 9:29 PM Jose Cheyo Jimenez <cheyo@masters3d.com <mailto:cheyo@masters3d.com>> wrote:

On Oct 6, 2017, at 8:58 PM, Tony Allevato <tony.allevato@gmail.com <mailto:tony.allevato@gmail.com>> wrote:
On Fri, Oct 6, 2017 at 8:45 PM Jose Cheyo Jimenez <cheyo@masters3d.com <mailto:cheyo@masters3d.com>> wrote:

On Oct 6, 2017, at 8:01 PM, Tony Allevato <tony.allevato@gmail.com <mailto:tony.allevato@gmail.com>> wrote:

private class MyClass {
    static func myFunc(){ // This would now act differently from private extensions?
        print("acts like fileprivate now")
    }
}

private class MyClass2 {}

private extension MyClass2{
      static func myFunc2(){
       print("Same as MyClass.myFunc")
    }
}

MyClass.myFunc() // acts like fileprivate
MyClass2.myFunc2() // The proposed change would hide myFunc2
             //Error: 'myFunc2' is inaccessible due to 'private' protection level

hartbit · October 7, 2017, 3:26pm

One argument: without this fix, private is the only access level for which we have no means to easily and implicitly apply an access level to a group of members. And it bums me to have to explicitly type private on ever single member to achieve the same result as I can with any other access level.

···

On 7 Oct 2017, at 07:07, Jose Cheyo Jimenez via swift-evolution <swift-evolution@swift.org> wrote:

On Oct 6, 2017, at 9:35 PM, Tony Allevato <tony.allevato@gmail.com> wrote:

On Fri, Oct 6, 2017 at 9:29 PM Jose Cheyo Jimenez <cheyo@masters3d.com> wrote:

On Oct 6, 2017, at 8:58 PM, Tony Allevato <tony.allevato@gmail.com> wrote:

On Fri, Oct 6, 2017 at 8:45 PM Jose Cheyo Jimenez <cheyo@masters3d.com> wrote:

On Oct 6, 2017, at 8:01 PM, Tony Allevato <tony.allevato@gmail.com> wrote:

At the time SE-0025 was accepted, "private extension" would have been meaningless if it did not mean "fileprivate" because it predated the SE-0169 behavior extending "private" to extensions in the same file. The very issue being debated here is whether the oversight that SE-0169 did not consider extensions—now that "private extension" *could* have a meaningful use separate from "fileprivate extension"—is something that is worth correcting.

If the documentation is out-of-date and needs to be updated to list describe unintuitive special behavior, why not use the opportunity to make the behavior intuitive and consistent instead?

Lets say you “fix” the private extension override. Now MyClass2.myFunc2() is not accessible from outside the type.
Wouldn't MyClass2.myFunc2() now be inconsistent with MyClass.myFunc()?
I don’t think you can make a change to one with out causing other inconsistencies. I rest my case.

No, because a class is a concrete "thing" whose access level which—while providing an upper bound for access levels of its defaulting members—is otherwise independent of the access level of its members.

Extensions, on the other hand, aren't a concrete thing of their own. The access level on an extension exists *solely* as a shortcut to specify the upper bound for its defaulting members that are injected into the main type.

What happens in your example if you replace "private" with "public"? Then myFunc has internal access but myFunc2 is public. So the "inconsistency" you're pointing out between access inherited from a type and access inherited from an extension already exists—they're apples and oranges.

That's why access levels of classes/structs/other types aren't relevant examples here—extensions treat access levels fundamentally differently.

Sure. Extensions apply a default upper bound and types can lower the upper bound of the default internal members. The upper bound on the below example is the same for both when dealing with top level private.

Extensions should resolve their upper bound accessibility where the ‘private’ appears explicitly and this now happens to be the same for both types and extensions regardless of how they are enforced.

But *why* do you think that should be? You're stating what the current situation is and you say that it "should" be that way, but why should we accept that status quo instead of making "private extension" more useful for people who use "private" in the sense introduced by SE-0169, when the argument for consistency can honestly be argued either way (the two options I wrote a few messages up)?

Oh Because I believe that lowering the scope of “private extension” would undermine the spirit of 169. 169 was a compromise after 159 was rejected. 169 was meant to make fileprivate less common and thus more meaningful when it occurs in source. Where 169 was meant to relax the rules, the proposed “fix” would force people who now use “private extension” to use “fileprivate extension” thus making fileprivate more common. In other words, 169 was about relaxing rules and not about tightening down the rules or allowing “true” private to be applied as a default ACL extension.

“scoped" `private extension` can’t be archived now in the same way that ‘open extension’ is not allowed. The lowest and highest ACL are not able to be applied as default extension modifiers and this makes sense to me.

There is no solution that will make everyone happy: maintaining the status quo makes “fileprivate” too common and therefore not meaningful when it occurs in source; removing or diluting scope-level access control (as in SE-0159 <https://github.com/apple/swift-evolution/blob/master/proposals/0159-fix-private-access-levels.md> and this proposal)
https://lists.swift.org/pipermail/swift-evolution-announce/2017-April/000357.html

private class MyClass {
    static func myFunc(){ // This would now act differently from private extensions?
        print("acts like fileprivate now")
    }
}

private class MyClass2 {}

private extension MyClass2{
      static func myFunc2(){
       print("Same as MyClass.myFunc")
    }
}

MyClass.myFunc() // acts like fileprivate
MyClass2.myFunc2() // The proposed change would hide myFunc2
             //Error: 'myFunc2' is inaccessible due to 'private' protection level

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

xwu · October 7, 2017, 3:28pm

This, I think, is the most persuasive argument available here; it provides
a concrete use case to justify why one design is superior to the other.

···

On Sat, Oct 7, 2017 at 10:26 David Hart via swift-evolution < swift-evolution@swift.org> wrote:

One argument: without this fix, private is the only access level for which
we have no means to easily and implicitly apply an access level to a group
of members. And it bums me to have to explicitly type private on ever
single member to achieve the same result as I can with any other access
level.

On 7 Oct 2017, at 07:07, Jose Cheyo Jimenez via swift-evolution < > swift-evolution@swift.org> wrote:

On Oct 6, 2017, at 9:35 PM, Tony Allevato <tony.allevato@gmail.com> wrote:

On Fri, Oct 6, 2017 at 9:29 PM Jose Cheyo Jimenez <cheyo@masters3d.com> > wrote:

On Oct 6, 2017, at 8:58 PM, Tony Allevato <tony.allevato@gmail.com> >> wrote:

On Fri, Oct 6, 2017 at 8:45 PM Jose Cheyo Jimenez <cheyo@masters3d.com> >> wrote:

On Oct 6, 2017, at 8:01 PM, Tony Allevato <tony.allevato@gmail.com> >>> wrote:

At the time SE-0025 was accepted, "private extension" would have been

meaningless if it did not mean "fileprivate" because it predated the
SE-0169 behavior extending "private" to extensions in the same file. The
very issue being debated here is whether the oversight that SE-0169 did not
consider extensions—now that "private extension" *could* have a meaningful
use separate from "fileprivate extension"—is something that is worth
correcting.

If the documentation is out-of-date and needs to be updated to list
describe unintuitive special behavior, why not use the opportunity to make
the behavior intuitive and consistent instead?

Lets say you “fix” the private extension override. Now
MyClass2.myFunc2() is not accessible from outside the type.
Wouldn't MyClass2.myFunc2() now be inconsistent with MyClass.myFunc()?
I don’t think you can make a change to one with out causing other
inconsistencies. I rest my case.

No, because a class is a concrete "thing" whose access level which—while
providing an upper bound for access levels of its defaulting members—is
otherwise independent of the access level of its members.

Extensions, on the other hand, aren't a concrete thing of their own. The
access level on an extension exists *solely* as a shortcut to specify the
upper bound for its defaulting members that are injected into the main type.

What happens in your example if you replace "private" with "public"? Then
myFunc has internal access but myFunc2 is public. So the "inconsistency"
you're pointing out between access inherited from a type and access
inherited from an extension already exists—they're apples and oranges.

That's why access levels of classes/structs/other types aren't relevant
examples here—extensions treat access levels fundamentally differently.

Sure. Extensions apply a default upper bound and types can lower the
upper bound of the default internal members. The upper bound on the below
example is the same for both when dealing with top level private.

Extensions should resolve their upper bound accessibility where the
‘private’ appears explicitly and this now happens to be the same for both
types and extensions regardless of how they are enforced.

But *why* do you think that should be? You're stating what the current
situation is and you say that it "should" be that way, but why should we
accept that status quo instead of making "private extension" more useful
for people who use "private" in the sense introduced by SE-0169, when the
argument for consistency can honestly be argued either way (the two options
I wrote a few messages up)?

Oh Because I believe that lowering the scope of “private extension”
would undermine the spirit of 169. 169 was a compromise after 159 was
rejected. 169 was meant to make fileprivate less common and thus more
meaningful when it occurs in source. Where 169 was meant to relax the
rules, the proposed “fix” would force people who now use “private
extension” to use “fileprivate extension” thus making fileprivate more
common. In other words, 169 was about relaxing rules and not about
tightening down the rules or allowing “true” private to be applied as a
default ACL extension.

“scoped" `private extension` can’t be archived now in the same way that
‘open extension’ is not allowed. The lowest and highest ACL are not able to
be applied as default extension modifiers and this makes sense to me.

There is no solution that will make everyone happy: maintaining the status quo makes “fileprivate” too common and therefore not meaningful when it occurs in source; removing or diluting scope-level access control (as in SE-0159 <https://github.com/apple/swift-evolution/blob/master/proposals/0159-fix-private-access-levels.md> and this proposal)

https://lists.swift.org/pipermail/swift-evolution-announce/2017-April/000357.html

private class MyClass {
    static func myFunc(){ // This would now act differently from
private extensions?
        print("acts like fileprivate now")
    }
}

private class MyClass2 {}

private extension MyClass2{
      static func myFunc2(){
       print("Same as MyClass.myFunc")
    }
}

MyClass.myFunc() // acts like fileprivate
MyClass2.myFunc2() // The proposed change would hide myFunc2
             //Error: 'myFunc2' is inaccessible due to 'private'
protection level

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

masters3d · October 7, 2017, 5:21pm

This, I think, is the most persuasive argument available here; it provides a concrete use case to justify why one design is superior to the other.

open extension do not exist either.

···

On Oct 7, 2017, at 8:28 AM, Xiaodi Wu <xiaodi.wu@gmail.com> wrote:

On Sat, Oct 7, 2017 at 10:26 David Hart via swift-evolution <swift-evolution@swift.org> wrote:
One argument: without this fix, private is the only access level for which we have no means to easily and implicitly apply an access level to a group of members. And it bums me to have to explicitly type private on ever single member to achieve the same result as I can with any other access level.

In the same way that we need to be explicit about open in extension members or public in public type members; the lowest access version of scope private needs to also be explicit in private extension members and top level private concrete type members.

The premise of 169 was never about creating a new version of scope private that could only be used in extensions. It just relaxed the rules for explicit private extension members.

xwu · October 7, 2017, 5:23pm

This, I think, is the most persuasive argument available here; it provides
a concrete use case to justify why one design is superior to the other.

open extension do not exist either.

That could be fixed too then.

···

On Sat, Oct 7, 2017 at 12:21 Jose Cheyo Jimenez <cheyo@masters3d.com> wrote:

On Oct 7, 2017, at 8:28 AM, Xiaodi Wu <xiaodi.wu@gmail.com> wrote:

On Sat, Oct 7, 2017 at 10:26 David Hart via swift-evolution < > swift-evolution@swift.org> wrote:

One argument: without this fix, private is the only access level for which

we have no means to easily and implicitly apply an access level to a group
of members. And it bums me to have to explicitly type private on ever
single member to achieve the same result as I can with any other access
level.

In the same way that we need to be explicit about open in extension
members or public in public type members; the lowest access version of
scope private needs to also be explicit in private extension members and
top level private concrete type members.

The premise of 169 was never about creating a new version of scope private
that could only be used in extensions. It just relaxed the rules for
explicit private extension members.