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.[swift-evolution-announce] [Core team] Addressing the SE-0110 usability regression in Swift 4
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.(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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