[Proposal] Change Void meaning

[hartbit (David Hart)]

Unfortunately, I think this proposal appears to be mistaken as to this key premise: Void was never (IIUC) meant to model the absence of arguments; it is a type with one possible value.

If I recall, a number of conversations have been raised about Void being a typealias of (), and the definitive response has been that this falls into the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a particular coding style have to do with loss of implicit tuple splatting, the cure for which is a proper implementation of tuple splatting, not poking holes into settled parts of the type system.

But you can’t deny that SE-0110 has also caused regressions in the use of Void as generic argument because Void is modelled as the empty tuple. And tuple splatting will not fix those regressions.

And contrary to what some people might think, this is not an “edge-case”. Most useful monads modelled with generics have good reasons to use Void:

The Result<T> monad: Result<Void> represents the result of an operation with no return value
The Promise<T> monad: Promise<Void> represents the result of an asynchronous operation with no return value
The Observable<T> monad (in functional reactive programming): Observable<Void> represents a stream of events with no values

I use all three monads in my code and I’ve had to modify a lot of code when migrating to Swift 4 beta1 because of Void.

David.

···

On 12 Jun 2017, at 19:25, Xiaodi Wu via swift-evolution <swift-evolution@swift.org> wrote:

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about tuples usage.

After documenting myself about the changes which happened, I thought that they could be improved. Instead of fighting these propositions (which make sense), I wanted create a few proposal which would improve these recent changes with a few simple rules.

My propositions are based on the recent decisions and in the continuation of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not parameters. I'm not sure there was ever much point in writing Void in a parameter list, but whatever reasons there were surely vanished with SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI gave it a new purpose it with void*, but the meaning is totally unrelated.

John.
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[VladimirS (Vladimir)]

Thank you for reply, but actually I was trying to figure out if I understand correctly "what any of these *should* do in Swift 4". Also, it will be great if we have a record of how such code at least *should* work in Swift 4, so we can refer to this.

So, again, I'm asking you or some one from core team to spent 1 minute to reply so we all have a clear view of expected results for this code. Thank you.

I do believe this is very important in lights of current debates regarding SE-0110 changes(actually, I insist, more correct implementations of SE-0066) and probably can help to avoid the same problem after "bugs" will be fixed.

Btw, it is *very* strange for me that you are calling current behavior as "bugs", and even strange that these long-running "bugs" can be still with us in Swift 4 (note: SE-0066 and SE-0110 was accepted to be implemented in *Swift 3*).

And more important, as I understand, fixing these "bugs" will lead to *source breaking* changes, that is not possible for long time after Swift 4 release.
Plus, keeping these "bugs" leaves Swift in very broken state : we broke what was allowed in Swift 3 to fix the type system, but still have type system broken *in the same exact place*.

I really can't understand this. It is fundamentally that
type(of: fooParam) == type(of: fooTuple) even in Swift 4, it is not just a little "bug", code *will* use this "feature" and then we'll have a very loud voices about regressions in Swift if such "bug" will be "fixed". The same is for
fooParam is ((Int,Int))->() and fooTuple is (Int,Int)->() and so on.
I can't see how this could be a bug fixing - it is fundamental changes in allowed syntax and in type system. And so this couldn't be done after Swift 4 release. No?

About this:

···

On 13.06.2017 3:35, John McCall wrote:

On Jun 12, 2017, at 6:42 PM, Vladimir.S <svabox@gmail.com> wrote:

John, could you clarify the details regarding function types, SE-0066 and SE-0110 implementations *planned* for Swift 4 release? I believe all these are important questions to be answered to understand the near feature of Swift and to be prepared for changes.

It's not hard to figure out what any of these *should* do in Swift 4. I'm not going to commit to promising that Swift 4 will not have bugs that cause deviations from that. If the Core Team decides that something needs to happen with parameter destructuring in Swift 4, that will not go without comment here.

----
On 13.06.2017 2:24, Jens Persson wrote:
> This: https://twitter.com/slava_pestov/status/874394132340289536
> seems to suggest that the current Swift 4 behavior will not change much in this domain.
>
----

It will be really *nice* to have a more detailed reply from core team regarding all this situation with SE-0025, SE-0066, SE-0110 implementations in Swift 4 and the "bugs" mentioned in my message, here in official swift evolution email list.

Vladimir.

John.

Given :

func fooParam(_ x: Int, _ y: Int){}
func fooTuple(_ x: (Int, Int)) {}

and

var closureParam = { (x: Int, y: Int) in print("in closureParam") }
var closureTuple = { (x: (Int, Int)) in }

* What will be the result in Swift 4 release? :
  1. type(of:fooParam)
  2. type(of:fooTuple)
  3. type(of:closureParam)
  4. type(of:closureTuple)

* Will this be true in Swift 4 release? :
  1. type(of: fooParam) == type(of: fooTuple)
  2. fooParam is ((Int,Int))->()
  3. fooTuple is (Int,Int)->()
  4. type(of: closureParam) == type(of: closureTuple)
  5. closureParam is ((Int,Int))->()
  6. closureTuple is (Int,Int)->()

* Will this code still be valid in Swift 4 release? :
  1.
  closureTuple = closureParam
  closureTuple((1,2)) // prints "in closureParam"

  2.
  var f: () -> Int = { 5 } // function with no parameters
  var g: (()) -> Int = { 5 } // function taking a single () parameter
  f = g
  f()

* Does core team plan to introduce some syntactic sugar for tuple argument destructuring in closures *before* Swift 4 release?
If so, what do you think about a suggestion to allow type inference for currently allowed syntax for tuple argument destructuring? I.e.
allowed: .filter {(friend: (name: String, age: Int)) in friend.age >= 18 }
proposed: .filter {(friend: (name, age)) in friend.age >= 18 }

* And the same for passing function with no parameters if function with single Void parameter is expected? I.e. in such situation:
func foo<T>(_ callback: (T)->Void) {}
func bar(){}
foo(bar)

Thank you for your time.
Vladimir.

On 12.06.2017 20:15, John McCall via swift-evolution wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about tuples usage.

After documenting myself about the changes which happened, I thought that they could be improved. Instead of fighting these propositions (which make sense), I wanted create a few proposal which would improve these recent changes with a few simple rules.

My propositions are based on the recent decisions and in the continuation of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not parameters. I'm not sure there was ever much point in writing Void in a parameter list, but whatever reasons there were surely vanished with SE-0066.
Note that 'void' in C was originally exclusively a return type. ANSI gave it a new purpose it with void*, but the meaning is totally unrelated.
John.
_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution

[Jeremie_Girault (Jérémie Girault)]

@xiaodi
I disagree on many points, for example what is the type of x when we type
`let x = *Void` ?
This is the essence of the problem and this proposition wants to solve this.

The regression is due to both reason combined : typealias Void = () AND
SE-0110

My proposition is to change the meaning of Void from () to “something else”
that is type-compatible with SE-0110 (and splatting in the future).

If you want an example of the changes needed to migrate to swift4, just
look at the 42 files of handling parenthesis PR of RxSwift needed for
swift4 upgrade : Compile under Swift 4 by volodg · Pull Request #1282 · ReactiveX/RxSwift · GitHub

···

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 21:18:06, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:05 PM, David Hart <david@hartbit.com> wrote:

On 12 Jun 2017, at 19:25, Xiaodi Wu via swift-evolution < > swift-evolution@swift.org> wrote:

Unfortunately, I think this proposal appears to be mistaken as to this key
premise: Void was never (IIUC) meant to model the absence of arguments; it
is a type with one possible value.

If I recall, a number of conversations have been raised about Void being a
typealias of (), and the definitive response has been that this falls into
the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a
particular coding style have to do with loss of implicit tuple splatting,
the cure for which is a proper implementation of tuple splatting, not
poking holes into settled parts of the type system.

But you can’t deny that SE-0110 has also caused regressions in the use of
Void as generic argument because Void is modelled as the empty tuple.

I'm not sure I understand this statement. Void is a synonym for the empty
tuple, and that hasn't ever changed, so it can't be the root cause of any
regressions.

And tuple splatting will not fix those regressions.

How come? If `*` is the splat operator, then it would be legal to call a
function `foo` that takes no arguments with `foo(*Void)`; if implicit tuple
splatting returns in fully implemented form, then it would be legal to call
it once again with `foo(Void)`.

And contrary to what some people might think, this is not an “edge-case”.

Most useful monads modelled with generics have good reasons to use Void:

*The Result<T> monad:* Result<Void> represents the result of an operation
with no return value
*The Promise<T> monad:* Promise<Void> represents the result of an
asynchronous operation with no return value
*The Observable<T> monad (in functional reactive programming):*
Observable<Void> represents a stream of events with no values

I use all three monads in my code and I’ve had to modify a lot of code
when migrating to Swift 4 beta1 because of Void.

Can you give examples of the modifications needed during migration? From
here, I can only see that the reason any code needs modification is the
complete removal of implicit tuple splatting. Nothing has changed about
Void being a synonym for the empty tuple; even if you rename Void,
functions will still return () by some other name, and unless there is
tuple splatting in some form, the migration you performed is inevitable.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution < > swift-evolution@swift.org> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution < >> swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about
tuples usage.

After documenting myself about the changes which happened, I thought that
they could be improved. Instead of fighting these propositions (which make
sense), I wanted create a few proposal which would improve these recent
changes with a few simple rules.

My propositions are based on the recent decisions and in the continuation
of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason
of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not parameters.
I'm not sure there was ever much point in writing Void in a parameter list,
but whatever reasons there were surely vanished with SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI
gave it a new purpose it with void*, but the meaning is totally unrelated.

John.
_______________________________________________
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

[Jeremie_Girault (Jérémie Girault)]

@Xiaodi Wu
Disagree, and we would need the original designer here to help us, but my
understanding of the original meaning of tuples-as-arguments is that when I
define:
`func foo(_ arg0: Any, _ arg1: Any) {}`
I can afterwards “apply” a tuple to a function named `foo` and therefore
execute the function on this tuple.
Calling a function syntax was equivalent to put a tuple next to a function
name:
`foo(42, “hello")` the left-hand is `foo`, the right-hand is `(42,
“hello")` is the tuple.

The same way if I have
`func foo()`
`foo()` means calling `foo` with argument `()` and there we have our
original `Void`

That meaning changed recently due to multiple SE implementations actually.
The parenthesis around the call don't have a tuple meaning anymore.
Therefore it breaks a lot of code relying on this feature of the language,
which was quite elegant, but could not handle advanced functions features.

@john: Void can happen easily in parameters due to generics, the easiest
example that breaks with swift4 is
`typealias Callback<T> = (T) -> Void`
here
`Callback<Void>` which is perfectly reasonable introduces Void in the
argument list and forces the caller to introduces an empty partenthesis set
when invoking:

let foo: Callback<Void> = { }
foo(())

That’s were the proposal shines in my opinion: adapting the meaning of Void
to the current context of swift4 gives back the language the elegant syntax
it had while preserving the type system

···

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 20:04:18, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 12:44 Jérémie Girault <jeremie.girault@gmail.com> wrote:

Void was the empty tuple because arguments were tuples.

As John explained, that is _not_ correct. Void was not motivated by
anything to do with argument lists.

So no arguments meant empty tuple.

If we consider the empty tuple to be an argument, then the type for the
type of empty tuple should be `Unit`

It has been suggested to rename Void to Unit. I do believe it’s on the
commonly rejected ideas list (and if it’s not, it ought to be).

Void, however, seem naturally fitted for the absence of argument.

Should `func foo(Void)` be different from `func foo()`?

SE-0110 determined that the two should in fact be different.

I don’t think so. But different from `func foo(Unit)` ? Yes !

It sounds like your quarrel is with the name of the typealias. I don’t see
how that solves any issues with the loss of tuple splatting. Functions will
still return (), and you foo(()) is not foo().

My point here is that we probably won’t have splatting for swift4.

But if we consider the type system as a guide, we can consider 3 simple
set of rules and restore almost 100% source compatibility while keeping the
improvement of SE-0110
- Rules for swift3 tuples-arguments of cardinality zero (Void) in swift 4
(this proposition)
- Rules for swift3 tuples-arguments of cardinality one in swift 4
(proposition to be done)
- Rules for swift3 tuples-arguments of cardinality > 1 in swift 4
(proposition to be done)

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 19:25:31, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

Unfortunately, I think this proposal appears to be mistaken as to this key
premise: Void was never (IIUC) meant to model the absence of arguments; it
is a type with one possible value.

If I recall, a number of conversations have been raised about Void being a
typealias of (), and the definitive response has been that this falls into
the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a
particular coding style have to do with loss of implicit tuple splatting,
the cure for which is a proper implementation of tuple splatting, not
poking holes into settled parts of the type system.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution < > swift-evolution@swift.org> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution < >> swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about
tuples usage.

After documenting myself about the changes which happened, I thought that
they could be improved. Instead of fighting these propositions (which make
sense), I wanted create a few proposal which would improve these recent
changes with a few simple rules.

My propositions are based on the recent decisions and in the continuation
of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason
of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not parameters.
I'm not sure there was ever much point in writing Void in a parameter list,
but whatever reasons there were surely vanished with SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI
gave it a new purpose it with void*, but the meaning is totally unrelated.

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

[Jeremie_Girault (Jérémie Girault)]

Exactly, that means that your implementation of the tuple splatting
operator is out of the type system.
Can you expose it’s signature ?

If you want the operator to be “compiler-magic” it’s possible.
This proposal is an alternate solution.

My point is that updating Void according to this proposal would
- preserve the type system in a better way
- have better source compatibility (in time for swift 4 release, were we
probably won’t see tuple splatting)
- also keep the elegant original syntax of swift instead of stacking
parenthesis

The impact for code writers would be minimized on time for swift 4 release

As for return values: this proposition does not intend to change the how
return value of Void functions works.

···

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 21:45:08, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:32 PM, Jérémie Girault <jeremie.girault@gmail.com> wrote:

@xiaodi
I disagree on many points, for example what is the type of x when we type
`let x = *Void` ?

That would not be a legal statement. Exploding a tuple is an operation that
only makes sense inside an argument list. Likewise `let x = &Void` will not
compile.

This is the essence of the problem and this proposition wants to solve
this.

The regression is due to both reason combined : typealias Void = () AND
SE-0110

My proposition is to change the meaning of Void from () to “something
else” that is type-compatible with SE-0110 (and splatting in the future).

I'm not sure I understand your motivation. Void is just a typealias. If
tomorrow Void meant something else, all functions must still return (), and
there is still no implicit tuple splatting.

If you want an example of the changes needed to migrate to swift4, just
look at the 42 files of handling parenthesis PR of RxSwift needed for
swift4 upgrade : Compile under Swift 4 by volodg · Pull Request #1282 · ReactiveX/RxSwift · GitHub

Indeed, that's the result of SE-0110; these parentheses are needed because
there is no implicit tuple splatting. They would be required even if `Void`
did not exist in the language at all.

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 21:18:06, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:05 PM, David Hart <david@hartbit.com> wrote:

On 12 Jun 2017, at 19:25, Xiaodi Wu via swift-evolution < >> swift-evolution@swift.org> wrote:

Unfortunately, I think this proposal appears to be mistaken as to this
key premise: Void was never (IIUC) meant to model the absence of arguments;
it is a type with one possible value.

If I recall, a number of conversations have been raised about Void being
a typealias of (), and the definitive response has been that this falls
into the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a
particular coding style have to do with loss of implicit tuple splatting,
the cure for which is a proper implementation of tuple splatting, not
poking holes into settled parts of the type system.

But you can’t deny that SE-0110 has also caused regressions in the use of
Void as generic argument because Void is modelled as the empty tuple.

I'm not sure I understand this statement. Void is a synonym for the empty
tuple, and that hasn't ever changed, so it can't be the root cause of any
regressions.

And tuple splatting will not fix those regressions.

How come? If `*` is the splat operator, then it would be legal to call a
function `foo` that takes no arguments with `foo(*Void)`; if implicit tuple
splatting returns in fully implemented form, then it would be legal to call
it once again with `foo(Void)`.

And contrary to what some people might think, this is not an “edge-case”.

Most useful monads modelled with generics have good reasons to use Void:

*The Result<T> monad:* Result<Void> represents the result of an
operation with no return value
*The Promise<T> monad:* Promise<Void> represents the result of an
asynchronous operation with no return value
*The Observable<T> monad (in functional reactive programming):* Observable<Void>
represents a stream of events with no values

I use all three monads in my code and I’ve had to modify a lot of code
when migrating to Swift 4 beta1 because of Void.

Can you give examples of the modifications needed during migration? From
here, I can only see that the reason any code needs modification is the
complete removal of implicit tuple splatting. Nothing has changed about
Void being a synonym for the empty tuple; even if you rename Void,
functions will still return () by some other name, and unless there is
tuple splatting in some form, the migration you performed is inevitable.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution < >> swift-evolution@swift.org> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution < >>> swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about
tuples usage.

After documenting myself about the changes which happened, I thought
that they could be improved. Instead of fighting these propositions (which
make sense), I wanted create a few proposal which would improve these
recent changes with a few simple rules.

My propositions are based on the recent decisions and in the
continuation of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason
of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not
parameters. I'm not sure there was ever much point in writing Void in a
parameter list, but whatever reasons there were surely vanished with
SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI
gave it a new purpose it with void*, but the meaning is totally unrelated.

John.
_______________________________________________
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

[Jeremie_Girault (Jérémie Girault)]

I invite you to read the proposal rules again with a fresh mindset and
benevolence spirit.
It’s my first one and may not be very clear but the rules are
straightforward.

Especially try to forget that Void is a tuple or anything.
Void is Nothing in the programmer’s mind. An instance of Void shouldn’t
even exist.

The proposed meaning of Void is to be a “lack” of arguments. It means that
each “Void” argument reduces the arity of the function by one, at its exact
position. Especially look at the canonical signature definition, and the
proposed rules of reduction.

That proposal, if implemented, would effectively allow `Callback<Void>` to
be called without arguments in the context of swift4.

···

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 22:06:54, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:56 PM, Jérémie Girault <jeremie.girault@gmail.com> wrote:

@Xiaodi Wu
Disagree, and we would need the original designer here to help us, but my
understanding of the original meaning of tuples-as-arguments is that when I
define:
`func foo(_ arg0: Any, _ arg1: Any) {}`
I can afterwards “apply” a tuple to a function named `foo` and therefore
execute the function on this tuple.
Calling a function syntax was equivalent to put a tuple next to a function
name:
`foo(42, “hello")` the left-hand is `foo`, the right-hand is `(42,
“hello")` is the tuple.

The same way if I have
`func foo()`
`foo()` means calling `foo` with argument `()` and there we have our
original `Void`

That meaning changed recently due to multiple SE implementations actually.

Tuples-as-arguments never shipped in any version of Swift, and the ability
to "apply" a tuple like that was removed by SE-0029--the original goal was
to implement this change in time for Swift 2.2.

The parenthesis around the call don't have a tuple meaning anymore.
Therefore it breaks a lot of code relying on this feature of the language,
which was quite elegant, but could not handle advanced functions features.

Yes, this is an intentional and approved part of SE-0029. The drawbacks
were enumerated in that proposal and were deemed acceptable.

@john: Void can happen easily in parameters due to generics, the easiest
example that breaks with swift4 is
`typealias Callback<T> = (T) -> Void`
here
`Callback<Void>` which is perfectly reasonable introduces Void in the
argument list and forces the caller to introduces an empty partenthesis set
when invoking:

let foo: Callback<Void> = { }
foo(())

`Callback<T> = (T) -> Void` refers to a callback that takes exactly one
argument. Since argument lists are not tuples, it is not possible to invoke
such a callback with zero arguments, or for that matter with two, three,
four, or five arguments.

That’s were the proposal shines in my opinion: adapting the meaning of Void

to the current context of swift4 gives back the language the elegant syntax
it had while preserving the type system

I'm not sure what you mean by this. No change in `Void` can cause a
function of type (T) -> Void to accept zero arguments: it requires one
argument of type T.

On 12 juin 2017 at 20:04:18, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 12:44 Jérémie Girault <jeremie.girault@gmail.com> > wrote:

Void was the empty tuple because arguments were tuples.

As John explained, that is _not_ correct. Void was not motivated by
anything to do with argument lists.

So no arguments meant empty tuple.

If we consider the empty tuple to be an argument, then the type for the
type of empty tuple should be `Unit`

It has been suggested to rename Void to Unit. I do believe it’s on the
commonly rejected ideas list (and if it’s not, it ought to be).

Void, however, seem naturally fitted for the absence of argument.

Should `func foo(Void)` be different from `func foo()`?

SE-0110 determined that the two should in fact be different.

I don’t think so. But different from `func foo(Unit)` ? Yes !

It sounds like your quarrel is with the name of the typealias. I don’t see
how that solves any issues with the loss of tuple splatting. Functions will
still return (), and you foo(()) is not foo().

My point here is that we probably won’t have splatting for swift4.

But if we consider the type system as a guide, we can consider 3 simple
set of rules and restore almost 100% source compatibility while keeping the
improvement of SE-0110
- Rules for swift3 tuples-arguments of cardinality zero (Void) in swift 4
(this proposition)
- Rules for swift3 tuples-arguments of cardinality one in swift 4
(proposition to be done)
- Rules for swift3 tuples-arguments of cardinality > 1 in swift 4
(proposition to be done)

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 19:25:31, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

Unfortunately, I think this proposal appears to be mistaken as to this
key premise: Void was never (IIUC) meant to model the absence of arguments;
it is a type with one possible value.

If I recall, a number of conversations have been raised about Void being
a typealias of (), and the definitive response has been that this falls
into the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a
particular coding style have to do with loss of implicit tuple splatting,
the cure for which is a proper implementation of tuple splatting, not
poking holes into settled parts of the type system.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution < >> swift-evolution@swift.org> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution < >>> swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about
tuples usage.

After documenting myself about the changes which happened, I thought
that they could be improved. Instead of fighting these propositions (which
make sense), I wanted create a few proposal which would improve these
recent changes with a few simple rules.

My propositions are based on the recent decisions and in the
continuation of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason
of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not
parameters. I'm not sure there was ever much point in writing Void in a
parameter list, but whatever reasons there were surely vanished with
SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI
gave it a new purpose it with void*, but the meaning is totally unrelated.

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

[Jeremie_Girault (Jérémie Girault)]

···

—

very short reply expected - vsre.info

Jérémie Girault

On 12 juin 2017 at 22:34:45, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 3:16 PM, Jérémie Girault jeremie.girault@gmail.com wrote:

I invite you to read the proposal rules again with a fresh mindset and benevolence spirit.

It’s my first one and may not be very clear but the rules are straightforward.

Especially try to forget that Void is a tuple or anything.

Void is Nothing in the programmer’s mind. An instance of Void shouldn’t even exist.

Sorry, that's not correct. Void is what's called Unit in other languages. It exists. That is why functions with "no return value" return Void. OTOH, Never does not exist. This discussion was had in great detail during the naming debate over Never.

Let’s put facts in front of correctness assertions. Is Void = Unit in C or c++ ? can you create instances of void in java ? you have Void for generics. https://en.wikipedia.org/wiki/Unit_type

And if you look at assembly, sending void or returning void actually means "nothing to push on the stack / nothing to pop”. Seems like having this stripping on signatures at compile-time could be great !

Actually, in my opinion we could discuss naming when we agree that the mechanism works, using this name is just a way to not impact the developer with code changes.

So either we agree on the fact that the mechanism works and we can move on to naming, or we get back on the topic : do you see a flaw in the proposal rules ? It elegantly transforms signature arity and provides the programmer a natural syntax to express it’s code.

The proposed meaning of Void is to be a “lack” of arguments. It means that each “Void” argument reduces the arity of the function by one, at its exact position. Especially look at the canonical signature definition, and the proposed rules of reduction.

I don't understand why you propose to name this new idea "Void". You're proposing something that's not even a lack of an argument, but an anti-argument, like anti-matter! I'm not sure I understand why this is necessary. It seems to be a very strange workaround for one specific issue arising from disallowing implicit tuple splatting.

Look at other languages, when you put Void in functions in C or java, do you need to add a value ? Ease of use is important.

You imply that I disagree with splatting were I don’t, let’s not make it personal. This proposal is even compatible with tuple splatting !

The proposal rules seem to work and provides great user value. Let’s try to consider this !

That proposal, if implemented, would effectively allow Callback<Void> to be called without arguments in the context of swift4.

—

very short reply expected - vsre.info

Jérémie Girault

On 12 juin 2017 at 22:06:54, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:56 PM, Jérémie Girault jeremie.girault@gmail.com wrote:

@Xiaodi Wu

Disagree, and we would need the original designer here to help us, but my understanding of the original meaning of tuples-as-arguments is that when I define:

func foo(_ arg0: Any, _ arg1: Any) {}

I can afterwards “apply” a tuple to a function named foo and therefore execute the function on this tuple.

Calling a function syntax was equivalent to put a tuple next to a function name:

foo(42, “hello") the left-hand is foo, the right-hand is (42, “hello") is the tuple.

The same way if I have

func foo()

foo() means calling foo with argument () and there we have our original Void

That meaning changed recently due to multiple SE implementations actually.

Tuples-as-arguments never shipped in any version of Swift, and the ability to "apply" a tuple like that was removed by SE-0029--the original goal was to implement this change in time for Swift 2.2.

The parenthesis around the call don't have a tuple meaning anymore. Therefore it breaks a lot of code relying on this feature of the language, which was quite elegant, but could not handle advanced functions features.

Yes, this is an intentional and approved part of SE-0029. The drawbacks were enumerated in that proposal and were deemed acceptable.

@john: Void can happen easily in parameters due to generics, the easiest example that breaks with swift4 is

typealias Callback<T> = (T) -> Void

here

Callback<Void> which is perfectly reasonable introduces Void in the argument list and forces the caller to introduces an empty partenthesis set when invoking:

let foo: Callback = { }

foo(())

Callback<T> = (T) -> Void refers to a callback that takes exactly one argument. Since argument lists are not tuples, it is not possible to invoke such a callback with zero arguments, or for that matter with two, three, four, or five arguments.

That’s were the proposal shines in my opinion: adapting the meaning of Void to the current context of swift4 gives back the language the elegant syntax it had while preserving the type system

I'm not sure what you mean by this. No change in Void can cause a function of type (T) -> Void to accept zero arguments: it requires one argument of type T.

On 12 juin 2017 at 20:04:18, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 12:44 Jérémie Girault jeremie.girault@gmail.com wrote:

Void was the empty tuple because arguments were tuples.

As John explained, that is not correct. Void was not motivated by anything to do with argument lists.

So no arguments meant empty tuple.

If we consider the empty tuple to be an argument, then the type for the type of empty tuple should be Unit

It has been suggested to rename Void to Unit. I do believe it’s on the commonly rejected ideas list (and if it’s not, it ought to be).

Void, however, seem naturally fitted for the absence of argument.

Should func foo(Void) be different from func foo()?

SE-0110 determined that the two should in fact be different.

I don’t think so. But different from func foo(Unit) ? Yes !

It sounds like your quarrel is with the name of the typealias. I don’t see how that solves any issues with the loss of tuple splatting. Functions will still return (), and you foo(()) is not foo().

My point here is that we probably won’t have splatting for swift4.

But if we consider the type system as a guide, we can consider 3 simple set of rules and restore almost 100% source compatibility while keeping the improvement of SE-0110

• Rules for swift3 tuples-arguments of cardinality zero (Void) in swift 4 (this proposition)

• Rules for swift3 tuples-arguments of cardinality one in swift 4 (proposition to be done)

• Rules for swift3 tuples-arguments of cardinality > 1 in swift 4 (proposition to be done)

—

very short reply expected - vsre.info

Jérémie Girault

On 12 juin 2017 at 19:25:31, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

Unfortunately, I think this proposal appears to be mistaken as to this key premise: Void was never (IIUC) meant to model the absence of arguments; it is a type with one possible value.

If I recall, a number of conversations have been raised about Void being a typealias of (), and the definitive response has been that this falls into the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a particular coding style have to do with loss of implicit tuple splatting, the cure for which is a proper implementation of tuple splatting, not poking holes into settled parts of the type system.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution swift-evolution@swift.org wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution swift-evolution@swift.org wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about tuples usage.

After documenting myself about the changes which happened, I thought that they could be improved. Instead of fighting these propositions (which make sense), I wanted create a few proposal which would improve these recent changes with a few simple rules.

My propositions are based on the recent decisions and in the continuation of SE-0110. The first one is about Void.

Void is historically defined as the type of the empty tuple. The reason of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not parameters. I'm not sure there was ever much point in writing Void in a parameter list, but whatever reasons there were surely vanished with SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI gave it a new purpose it with void*, but the meaning is totally unrelated.

John.

---

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

[xwu (Xiaodi Wu)]

Unfortunately, I think this proposal appears to be mistaken as to this key
premise: Void was never (IIUC) meant to model the absence of arguments; it
is a type with one possible value.

If I recall, a number of conversations have been raised about Void being a
typealias of (), and the definitive response has been that this falls into
the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a
particular coding style have to do with loss of implicit tuple splatting,
the cure for which is a proper implementation of tuple splatting, not
poking holes into settled parts of the type system.

But you can’t deny that SE-0110 has also caused regressions in the use of
Void as generic argument because Void is modelled as the empty tuple.

I'm not sure I understand this statement. Void is a synonym for the empty
tuple, and that hasn't ever changed, so it can't be the root cause of any
regressions.

And tuple splatting will not fix those regressions.

How come? If `*` is the splat operator, then it would be legal to call a
function `foo` that takes no arguments with `foo(*Void)`; if implicit tuple
splatting returns in fully implemented form, then it would be legal to call
it once again with `foo(Void)`.

And contrary to what some people might think, this is not an “edge-case”.

Most useful monads modelled with generics have good reasons to use Void:

*The Result<T> monad:* Result<Void> represents the result of an operation
with no return value
*The Promise<T> monad:* Promise<Void> represents the result of an
asynchronous operation with no return value
*The Observable<T> monad (in functional reactive programming):*
Observable<Void> represents a stream of events with no values

I use all three monads in my code and I’ve had to modify a lot of code
when migrating to Swift 4 beta1 because of Void.

Can you give examples of the modifications needed during migration? From
here, I can only see that the reason any code needs modification is the
complete removal of implicit tuple splatting. Nothing has changed about
Void being a synonym for the empty tuple; even if you rename Void,
functions will still return () by some other name, and unless there is
tuple splatting in some form, the migration you performed is inevitable.

···

On Mon, Jun 12, 2017 at 2:05 PM, David Hart <david@hartbit.com> wrote:

On 12 Jun 2017, at 19:25, Xiaodi Wu via swift-evolution < > swift-evolution@swift.org> wrote:

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution < > swift-evolution@swift.org> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution < >> swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about
tuples usage.

After documenting myself about the changes which happened, I thought that
they could be improved. Instead of fighting these propositions (which make
sense), I wanted create a few proposal which would improve these recent
changes with a few simple rules.

My propositions are based on the recent decisions and in the continuation
of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason
of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not parameters.
I'm not sure there was ever much point in writing Void in a parameter list,
but whatever reasons there were surely vanished with SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI
gave it a new purpose it with void*, but the meaning is totally unrelated.

John.
_______________________________________________
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

[Jeremie_Girault (Jérémie Girault)]

···

—

very short reply expected - vsre.info

Jérémie Girault

On 12 juin 2017 at 23:27:31, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 4:10 PM, Jérémie Girault jeremie.girault@gmail.com wrote:

—

very short reply expected - vsre.info

Jérémie Girault

On 12 juin 2017 at 22:34:45, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 3:16 PM, Jérémie Girault jeremie.girault@gmail.com wrote:

I invite you to read the proposal rules again with a fresh mindset and benevolence spirit.

It’s my first one and may not be very clear but the rules are straightforward.

Especially try to forget that Void is a tuple or anything.

Void is Nothing in the programmer’s mind. An instance of Void shouldn’t even exist.

Sorry, that's not correct. Void is what's called Unit in other languages. It exists. That is why functions with "no return value" return Void. OTOH, Never does not exist. This discussion was had in great detail during the naming debate over Never.

Let’s put facts in front of correctness assertions. Is Void = Unit in C or c++ ? can you create instances of void in java ? you have Void for generics. https://en.wikipedia.org/wiki/Unit_type

Sorry, I don't understand your line of argumentation. Fact: in Swift, Void is the name of the unit type. Are you objecting to the naming of the unit type in Swift? Do you want the unit type to have other features? Is there some other way of modeling the unit type other than a tuple of arity 0 that you prefer?

As I’m saying I’m not discussing the name. I propose to replace Void with another mechanism so that source compatibility is improved. Defining a unit type and names is trivial afterwards.

And if you look at assembly, sending void or returning void actually means "nothing to push on the stack / nothing to pop”. Seems like having this stripping on signatures at compile-time could be great !

Actually, in my opinion we could discuss naming when we agree that the mechanism works, using this name is just a way to not impact the developer with code changes.

So either we agree on the fact that the mechanism works and we can move on to naming, or we get back on the topic : do you see a flaw in the proposal rules ? It elegantly transforms signature arity and provides the programmer a natural syntax to express it’s code.

I have read your proposal three times, but I do not understand what it is proposing, in part because your proposal contains factual errors in the premises. For instance, it claims repeatedly that Void is a typealias for () because of something to do with argument lists, which is not true. It is therefore unclear to me what it is you are proposing to do and what is motivating such a proposal.

All I am saying is that, in previous conversations on this list, people who actually do the work of implementing features in the compiler have stated that typealias Void = () is a fait accompli. With that as a starting point, what do you propose to do?

You probably know the original designer intent better than me because you are here for a longer time, but that’s not the point. And thank you for trying to understand it again :

• The goal of the proposal is to replace Void by an intrinsic which would reduce the arity of argument list it is present in.

• Why ? Because, especially when using generics, Void will easily be introduced in parameter lists. Actually it introduces useless arguments. If you follow the rules in Detailed design, you will see that the reduction of arity will lead to a better source compatibility and syntax. Moreover the expected result, from a developer point of view, feels more natural.

The proposed meaning of Void is to be a “lack” of arguments. It means that each “Void” argument reduces the arity of the function by one, at its exact position. Especially look at the canonical signature definition, and the proposed rules of reduction.

I don't understand why you propose to name this new idea "Void". You're proposing something that's not even a lack of an argument, but an anti-argument, like anti-matter! I'm not sure I understand why this is necessary. It seems to be a very strange workaround for one specific issue arising from disallowing implicit tuple splatting.

Look at other languages, when you put Void in functions in C or java, do you need to add a value ? Ease of use is important.

You imply that I disagree with splatting were I don’t, let’s not make it personal. This proposal is even compatible with tuple splatting !

The proposal rules seem to work and provides great user value. Let’s try to consider this !

That proposal, if implemented, would effectively allow Callback<Void> to be called without arguments in the context of swift4.

—

very short reply expected - vsre.info

Jérémie Girault

On 12 juin 2017 at 22:06:54, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:56 PM, Jérémie Girault jeremie.girault@gmail.com wrote:

@Xiaodi Wu

Disagree, and we would need the original designer here to help us, but my understanding of the original meaning of tuples-as-arguments is that when I define:

func foo(_ arg0: Any, _ arg1: Any) {}

I can afterwards “apply” a tuple to a function named foo and therefore execute the function on this tuple.

Calling a function syntax was equivalent to put a tuple next to a function name:

foo(42, “hello") the left-hand is foo, the right-hand is (42, “hello") is the tuple.

The same way if I have

func foo()

foo() means calling foo with argument () and there we have our original Void

That meaning changed recently due to multiple SE implementations actually.

Tuples-as-arguments never shipped in any version of Swift, and the ability to "apply" a tuple like that was removed by SE-0029--the original goal was to implement this change in time for Swift 2.2.

The parenthesis around the call don't have a tuple meaning anymore. Therefore it breaks a lot of code relying on this feature of the language, which was quite elegant, but could not handle advanced functions features.

Yes, this is an intentional and approved part of SE-0029. The drawbacks were enumerated in that proposal and were deemed acceptable.

@john: Void can happen easily in parameters due to generics, the easiest example that breaks with swift4 is

typealias Callback<T> = (T) -> Void

here

Callback<Void> which is perfectly reasonable introduces Void in the argument list and forces the caller to introduces an empty partenthesis set when invoking:

let foo: Callback = { }

foo(())

Callback<T> = (T) -> Void refers to a callback that takes exactly one argument. Since argument lists are not tuples, it is not possible to invoke such a callback with zero arguments, or for that matter with two, three, four, or five arguments.

That’s were the proposal shines in my opinion: adapting the meaning of Void to the current context of swift4 gives back the language the elegant syntax it had while preserving the type system

I'm not sure what you mean by this. No change in Void can cause a function of type (T) -> Void to accept zero arguments: it requires one argument of type T.

On 12 juin 2017 at 20:04:18, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 12:44 Jérémie Girault jeremie.girault@gmail.com wrote:

Void was the empty tuple because arguments were tuples.

As John explained, that is not correct. Void was not motivated by anything to do with argument lists.

So no arguments meant empty tuple.

If we consider the empty tuple to be an argument, then the type for the type of empty tuple should be Unit

It has been suggested to rename Void to Unit. I do believe it’s on the commonly rejected ideas list (and if it’s not, it ought to be).

Void, however, seem naturally fitted for the absence of argument.

Should func foo(Void) be different from func foo()?

SE-0110 determined that the two should in fact be different.

I don’t think so. But different from func foo(Unit) ? Yes !

It sounds like your quarrel is with the name of the typealias. I don’t see how that solves any issues with the loss of tuple splatting. Functions will still return (), and you foo(()) is not foo().

My point here is that we probably won’t have splatting for swift4.

But if we consider the type system as a guide, we can consider 3 simple set of rules and restore almost 100% source compatibility while keeping the improvement of SE-0110

• Rules for swift3 tuples-arguments of cardinality zero (Void) in swift 4 (this proposition)

• Rules for swift3 tuples-arguments of cardinality one in swift 4 (proposition to be done)

• Rules for swift3 tuples-arguments of cardinality > 1 in swift 4 (proposition to be done)

—

very short reply expected - vsre.info

Jérémie Girault

On 12 juin 2017 at 19:25:31, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

Unfortunately, I think this proposal appears to be mistaken as to this key premise: Void was never (IIUC) meant to model the absence of arguments; it is a type with one possible value.

If I recall, a number of conversations have been raised about Void being a typealias of (), and the definitive response has been that this falls into the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a particular coding style have to do with loss of implicit tuple splatting, the cure for which is a proper implementation of tuple splatting, not poking holes into settled parts of the type system.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution swift-evolution@swift.org wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution swift-evolution@swift.org wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about tuples usage.

After documenting myself about the changes which happened, I thought that they could be improved. Instead of fighting these propositions (which make sense), I wanted create a few proposal which would improve these recent changes with a few simple rules.

My propositions are based on the recent decisions and in the continuation of SE-0110. The first one is about Void.

Void is historically defined as the type of the empty tuple. The reason of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not parameters. I'm not sure there was ever much point in writing Void in a parameter list, but whatever reasons there were surely vanished with SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI gave it a new purpose it with void*, but the meaning is totally unrelated.

John.

---

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

[xwu (Xiaodi Wu)]

@xiaodi
I disagree on many points, for example what is the type of x when we type
`let x = *Void` ?

That would not be a legal statement. Exploding a tuple is an operation that
only makes sense inside an argument list. Likewise `let x = &Void` will not
compile.

This is the essence of the problem and this proposition wants to solve
this.

The regression is due to both reason combined : typealias Void = () AND
SE-0110

My proposition is to change the meaning of Void from () to “something
else” that is type-compatible with SE-0110 (and splatting in the future).

I'm not sure I understand your motivation. Void is just a typealias. If
tomorrow Void meant something else, all functions must still return (), and
there is still no implicit tuple splatting.

If you want an example of the changes needed to migrate to swift4, just
look at the 42 files of handling parenthesis PR of RxSwift needed for
swift4 upgrade : Compile under Swift 4 by volodg · Pull Request #1282 · ReactiveX/RxSwift · GitHub

Indeed, that's the result of SE-0110; these parentheses are needed because
there is no implicit tuple splatting. They would be required even if `Void`
did not exist in the language at all.

···

On Mon, Jun 12, 2017 at 2:32 PM, Jérémie Girault <jeremie.girault@gmail.com> wrote:

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 21:18:06, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:05 PM, David Hart <david@hartbit.com> wrote:

On 12 Jun 2017, at 19:25, Xiaodi Wu via swift-evolution < >> swift-evolution@swift.org> wrote:

Unfortunately, I think this proposal appears to be mistaken as to this
key premise: Void was never (IIUC) meant to model the absence of arguments;
it is a type with one possible value.

If I recall, a number of conversations have been raised about Void being
a typealias of (), and the definitive response has been that this falls
into the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a
particular coding style have to do with loss of implicit tuple splatting,
the cure for which is a proper implementation of tuple splatting, not
poking holes into settled parts of the type system.

But you can’t deny that SE-0110 has also caused regressions in the use of
Void as generic argument because Void is modelled as the empty tuple.

I'm not sure I understand this statement. Void is a synonym for the empty
tuple, and that hasn't ever changed, so it can't be the root cause of any
regressions.

And tuple splatting will not fix those regressions.

How come? If `*` is the splat operator, then it would be legal to call a
function `foo` that takes no arguments with `foo(*Void)`; if implicit tuple
splatting returns in fully implemented form, then it would be legal to call
it once again with `foo(Void)`.

And contrary to what some people might think, this is not an “edge-case”.

Most useful monads modelled with generics have good reasons to use Void:

*The Result<T> monad:* Result<Void> represents the result of an
operation with no return value
*The Promise<T> monad:* Promise<Void> represents the result of an
asynchronous operation with no return value
*The Observable<T> monad (in functional reactive programming):*
Observable<Void> represents a stream of events with no values

I use all three monads in my code and I’ve had to modify a lot of code
when migrating to Swift 4 beta1 because of Void.

Can you give examples of the modifications needed during migration? From
here, I can only see that the reason any code needs modification is the
complete removal of implicit tuple splatting. Nothing has changed about
Void being a synonym for the empty tuple; even if you rename Void,
functions will still return () by some other name, and unless there is
tuple splatting in some form, the migration you performed is inevitable.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution < >> swift-evolution@swift.org> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution < >>> swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about
tuples usage.

After documenting myself about the changes which happened, I thought
that they could be improved. Instead of fighting these propositions (which
make sense), I wanted create a few proposal which would improve these
recent changes with a few simple rules.

My propositions are based on the recent decisions and in the
continuation of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason
of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not
parameters. I'm not sure there was ever much point in writing Void in a
parameter list, but whatever reasons there were surely vanished with
SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI
gave it a new purpose it with void*, but the meaning is totally unrelated.

John.
_______________________________________________
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

[xwu (Xiaodi Wu)]

@Xiaodi Wu
Disagree, and we would need the original designer here to help us, but my
understanding of the original meaning of tuples-as-arguments is that when I
define:
`func foo(_ arg0: Any, _ arg1: Any) {}`
I can afterwards “apply” a tuple to a function named `foo` and therefore
execute the function on this tuple.
Calling a function syntax was equivalent to put a tuple next to a function
name:
`foo(42, “hello")` the left-hand is `foo`, the right-hand is `(42,
“hello")` is the tuple.

The same way if I have
`func foo()`
`foo()` means calling `foo` with argument `()` and there we have our
original `Void`

That meaning changed recently due to multiple SE implementations actually.

Tuples-as-arguments never shipped in any version of Swift, and the ability
to "apply" a tuple like that was removed by SE-0029--the original goal was
to implement this change in time for Swift 2.2.

The parenthesis around the call don't have a tuple meaning anymore.
Therefore it breaks a lot of code relying on this feature of the language,
which was quite elegant, but could not handle advanced functions features.

Yes, this is an intentional and approved part of SE-0029. The drawbacks
were enumerated in that proposal and were deemed acceptable.

@john: Void can happen easily in parameters due to generics, the easiest
example that breaks with swift4 is
`typealias Callback<T> = (T) -> Void`
here
`Callback<Void>` which is perfectly reasonable introduces Void in the
argument list and forces the caller to introduces an empty partenthesis set
when invoking:

let foo: Callback<Void> = { }
foo(())

`Callback<T> = (T) -> Void` refers to a callback that takes exactly one
argument. Since argument lists are not tuples, it is not possible to invoke
such a callback with zero arguments, or for that matter with two, three,
four, or five arguments.

That’s were the proposal shines in my opinion: adapting the meaning of Void

to the current context of swift4 gives back the language the elegant syntax
it had while preserving the type system

I'm not sure what you mean by this. No change in `Void` can cause a
function of type (T) -> Void to accept zero arguments: it requires one
argument of type T.

···

On Mon, Jun 12, 2017 at 2:56 PM, Jérémie Girault <jeremie.girault@gmail.com> wrote:

On 12 juin 2017 at 20:04:18, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 12:44 Jérémie Girault <jeremie.girault@gmail.com> > wrote:

Void was the empty tuple because arguments were tuples.

As John explained, that is _not_ correct. Void was not motivated by
anything to do with argument lists.

So no arguments meant empty tuple.

If we consider the empty tuple to be an argument, then the type for the
type of empty tuple should be `Unit`

It has been suggested to rename Void to Unit. I do believe it’s on the
commonly rejected ideas list (and if it’s not, it ought to be).

Void, however, seem naturally fitted for the absence of argument.

Should `func foo(Void)` be different from `func foo()`?

SE-0110 determined that the two should in fact be different.

I don’t think so. But different from `func foo(Unit)` ? Yes !

It sounds like your quarrel is with the name of the typealias. I don’t see
how that solves any issues with the loss of tuple splatting. Functions will
still return (), and you foo(()) is not foo().

My point here is that we probably won’t have splatting for swift4.

But if we consider the type system as a guide, we can consider 3 simple
set of rules and restore almost 100% source compatibility while keeping the
improvement of SE-0110
- Rules for swift3 tuples-arguments of cardinality zero (Void) in swift 4
(this proposition)
- Rules for swift3 tuples-arguments of cardinality one in swift 4
(proposition to be done)
- Rules for swift3 tuples-arguments of cardinality > 1 in swift 4
(proposition to be done)

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 19:25:31, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

Unfortunately, I think this proposal appears to be mistaken as to this
key premise: Void was never (IIUC) meant to model the absence of arguments;
it is a type with one possible value.

If I recall, a number of conversations have been raised about Void being
a typealias of (), and the definitive response has been that this falls
into the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a
particular coding style have to do with loss of implicit tuple splatting,
the cure for which is a proper implementation of tuple splatting, not
poking holes into settled parts of the type system.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution < >> swift-evolution@swift.org> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution < >>> swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about
tuples usage.

After documenting myself about the changes which happened, I thought
that they could be improved. Instead of fighting these propositions (which
make sense), I wanted create a few proposal which would improve these
recent changes with a few simple rules.

My propositions are based on the recent decisions and in the
continuation of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason
of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not
parameters. I'm not sure there was ever much point in writing Void in a
parameter list, but whatever reasons there were surely vanished with
SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI
gave it a new purpose it with void*, but the meaning is totally unrelated.

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

[xwu (Xiaodi Wu)]

Exactly, that means that your implementation of the tuple splatting
operator is out of the type system.
Can you expose it’s signature ?

If you want the operator to be “compiler-magic” it’s possible.

Yes, it requires compiler support.

···

On Mon, Jun 12, 2017 at 3:04 PM, Jérémie Girault <jeremie.girault@gmail.com> wrote:

This proposal is an alternate solution.

My point is that updating Void according to this proposal would
- preserve the type system in a better way
- have better source compatibility (in time for swift 4 release, were we
probably won’t see tuple splatting)
- also keep the elegant original syntax of swift instead of stacking
parenthesis

The impact for code writers would be minimized on time for swift 4 release

As for return values: this proposition does not intend to change the how
return value of Void functions works.

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 21:45:08, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:32 PM, Jérémie Girault <jeremie.girault@ > gmail.com> wrote:

@xiaodi
I disagree on many points, for example what is the type of x when we type
`let x = *Void` ?

That would not be a legal statement. Exploding a tuple is an operation
that only makes sense inside an argument list. Likewise `let x = &Void`
will not compile.

This is the essence of the problem and this proposition wants to solve
this.

The regression is due to both reason combined : typealias Void = () AND
SE-0110

My proposition is to change the meaning of Void from () to “something
else” that is type-compatible with SE-0110 (and splatting in the future).

I'm not sure I understand your motivation. Void is just a typealias. If
tomorrow Void meant something else, all functions must still return (), and
there is still no implicit tuple splatting.

If you want an example of the changes needed to migrate to swift4, just
look at the 42 files of handling parenthesis PR of RxSwift needed for
swift4 upgrade : Compile under Swift 4 by volodg · Pull Request #1282 · ReactiveX/RxSwift · GitHub

Indeed, that's the result of SE-0110; these parentheses are needed because
there is no implicit tuple splatting. They would be required even if `Void`
did not exist in the language at all.

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 21:18:06, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:05 PM, David Hart <david@hartbit.com> wrote:

On 12 Jun 2017, at 19:25, Xiaodi Wu via swift-evolution < >>> swift-evolution@swift.org> wrote:

Unfortunately, I think this proposal appears to be mistaken as to this
key premise: Void was never (IIUC) meant to model the absence of arguments;
it is a type with one possible value.

If I recall, a number of conversations have been raised about Void being
a typealias of (), and the definitive response has been that this falls
into the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a
particular coding style have to do with loss of implicit tuple splatting,
the cure for which is a proper implementation of tuple splatting, not
poking holes into settled parts of the type system.

But you can’t deny that SE-0110 has also caused regressions in the use
of Void as generic argument because Void is modelled as the empty tuple.

I'm not sure I understand this statement. Void is a synonym for the empty
tuple, and that hasn't ever changed, so it can't be the root cause of any
regressions.

And tuple splatting will not fix those regressions.

How come? If `*` is the splat operator, then it would be legal to call a
function `foo` that takes no arguments with `foo(*Void)`; if implicit tuple
splatting returns in fully implemented form, then it would be legal to call
it once again with `foo(Void)`.

And contrary to what some people might think, this is not an “edge-case”.

Most useful monads modelled with generics have good reasons to use Void:

*The Result<T> monad:* Result<Void> represents the result of an
operation with no return value
*The Promise<T> monad:* Promise<Void> represents the result of an
asynchronous operation with no return value
*The Observable<T> monad (in functional reactive programming):* Observable<Void>
represents a stream of events with no values

I use all three monads in my code and I’ve had to modify a lot of code
when migrating to Swift 4 beta1 because of Void.

Can you give examples of the modifications needed during migration? From
here, I can only see that the reason any code needs modification is the
complete removal of implicit tuple splatting. Nothing has changed about
Void being a synonym for the empty tuple; even if you rename Void,
functions will still return () by some other name, and unless there is
tuple splatting in some form, the migration you performed is inevitable.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution < >>> swift-evolution@swift.org> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution < >>>> swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about
tuples usage.

After documenting myself about the changes which happened, I thought
that they could be improved. Instead of fighting these propositions (which
make sense), I wanted create a few proposal which would improve these
recent changes with a few simple rules.

My propositions are based on the recent decisions and in the
continuation of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason
of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not
parameters. I'm not sure there was ever much point in writing Void in a
parameter list, but whatever reasons there were surely vanished with
SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI
gave it a new purpose it with void*, but the meaning is totally unrelated.

John.
_______________________________________________
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

[Jeremie_Girault (Jérémie Girault)]

···

—

very short reply expected - vsre.info

Jérémie Girault

On 12 juin 2017 at 23:56:37, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 4:47 PM, Jérémie Girault jeremie.girault@gmail.com wrote:

• Void as arguments is pretty common when using generics, that’s a core point of this proposal. An maybe that’s why we misunderstood ourselves (around 0110 / 0066). This proposal addresses arguments.

• maybe it should be revised around this ? Simple example :

typealias Callback<T> = (T) -> Void -> Callback<Void> will give (Void) => Void.

It was acceptable before swift4 but no more. However nobody cares about this Void argument and actually we know it’s value. So why let the developer type it ?

Ah, I see. The purpose of SE-0029...SE-0110 was to make it possible to distinguish an argument list (Void) from an argument list (). This does cause some verbosity where previously users relied on implicit tuple splatting. Ideally, we would bring back some syntactic sugar to make this more ergonomic. But, whether or not the spelling is made more user-friendly, the point here is that everybody should care about this Void argument.

It is still be typechecked and appropriate errors should be reported to the user so nobody will ignore it.

But with the proposal the code will be striped out of Void arguments at compile-time. I think it's a win for the developer on a lot of grounds. The fact that this proposal integrates with the type-system is also important.

If you are not comfortable about Void being stripped, we can also discuss alternatives: someone was suggesting me that it would be possible to replace :

func foo<T, U, V>(t: T, u: U) -> V {

// do something with t and u

// return some V

}

with

func foo<Void, Int, String>(u: Int) -> String { let t = ()

// do something with t and u

// return some V

}

or

func foo<Void, Int, String>(t: Void = (), u: Int) -> String {

// do something with t and u

// return some V

}

I don’t know what you would consider more effective or elegant (at an implementation level) but it’s the same result for the developper.

My point here is that Void should be “striped” by “reducing” argument list signatures.

—

very short reply expected - vsre.info

Jérémie Girault

On 12 juin 2017 at 19:15:18, John McCall (rjmccall@apple.com) wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution swift-evolution@swift.org wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about tuples usage.

After documenting myself about the changes which happened, I thought that they could be improved. Instead of fighting these propositions (which make sense), I wanted create a few proposal which would improve these recent changes with a few simple rules.

My propositions are based on the recent decisions and in the continuation of SE-0110. The first one is about Void.

Void is historically defined as the type of the empty tuple. The reason of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not parameters. I'm not sure there was ever much point in writing Void in a parameter list, but whatever reasons there were surely vanished with SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI gave it a new purpose it with void*, but the meaning is totally unrelated.

John.

[xwu (Xiaodi Wu)]

I invite you to read the proposal rules again with a fresh mindset and
benevolence spirit.
It’s my first one and may not be very clear but the rules are
straightforward.

Especially try to forget that Void is a tuple or anything.
Void is Nothing in the programmer’s mind. An instance of Void shouldn’t
even exist.

Sorry, that's not correct. Void is what's called Unit in other languages.
It exists. That is why functions with "no return value" return Void. OTOH,
Never does not exist. This discussion was had in great detail during the
naming debate over Never.

The proposed meaning of Void is to be a “lack” of arguments. It means that
each “Void” argument reduces the arity of the function by one, at its exact
position. Especially look at the canonical signature definition, and the
proposed rules of reduction.

I don't understand why you propose to name this new idea "Void". You're
proposing something that's not even a lack of an argument, but an
anti-argument, like anti-matter! I'm not sure I understand why this is
necessary. It seems to be a very strange workaround for one specific issue
arising from disallowing implicit tuple splatting.

···

On Mon, Jun 12, 2017 at 3:16 PM, Jérémie Girault <jeremie.girault@gmail.com> wrote:

That proposal, if implemented, would effectively allow `Callback<Void>` to
be called without arguments in the context of swift4.

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 22:06:54, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:56 PM, Jérémie Girault < > jeremie.girault@gmail.com> wrote:

@Xiaodi Wu
Disagree, and we would need the original designer here to help us, but my
understanding of the original meaning of tuples-as-arguments is that when I
define:
`func foo(_ arg0: Any, _ arg1: Any) {}`
I can afterwards “apply” a tuple to a function named `foo` and therefore
execute the function on this tuple.
Calling a function syntax was equivalent to put a tuple next to a
function name:
`foo(42, “hello")` the left-hand is `foo`, the right-hand is `(42,
“hello")` is the tuple.

The same way if I have
`func foo()`
`foo()` means calling `foo` with argument `()` and there we have our
original `Void`

That meaning changed recently due to multiple SE implementations actually.

Tuples-as-arguments never shipped in any version of Swift, and the ability
to "apply" a tuple like that was removed by SE-0029--the original goal was
to implement this change in time for Swift 2.2.

The parenthesis around the call don't have a tuple meaning anymore.
Therefore it breaks a lot of code relying on this feature of the language,
which was quite elegant, but could not handle advanced functions features.

Yes, this is an intentional and approved part of SE-0029. The drawbacks
were enumerated in that proposal and were deemed acceptable.

@john: Void can happen easily in parameters due to generics, the easiest
example that breaks with swift4 is
`typealias Callback<T> = (T) -> Void`
here
`Callback<Void>` which is perfectly reasonable introduces Void in the
argument list and forces the caller to introduces an empty partenthesis set
when invoking:

let foo: Callback<Void> = { }
foo(())

`Callback<T> = (T) -> Void` refers to a callback that takes exactly one
argument. Since argument lists are not tuples, it is not possible to invoke
such a callback with zero arguments, or for that matter with two, three,
four, or five arguments.

That’s were the proposal shines in my opinion: adapting the meaning of

Void to the current context of swift4 gives back the language the elegant
syntax it had while preserving the type system

I'm not sure what you mean by this. No change in `Void` can cause a
function of type (T) -> Void to accept zero arguments: it requires one
argument of type T.

On 12 juin 2017 at 20:04:18, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 12:44 Jérémie Girault <jeremie.girault@gmail.com> >> wrote:

Void was the empty tuple because arguments were tuples.

As John explained, that is _not_ correct. Void was not motivated by
anything to do with argument lists.

So no arguments meant empty tuple.

If we consider the empty tuple to be an argument, then the type for the
type of empty tuple should be `Unit`

It has been suggested to rename Void to Unit. I do believe it’s on the
commonly rejected ideas list (and if it’s not, it ought to be).

Void, however, seem naturally fitted for the absence of argument.

Should `func foo(Void)` be different from `func foo()`?

SE-0110 determined that the two should in fact be different.

I don’t think so. But different from `func foo(Unit)` ? Yes !

It sounds like your quarrel is with the name of the typealias. I don’t
see how that solves any issues with the loss of tuple splatting. Functions
will still return (), and you foo(()) is not foo().

My point here is that we probably won’t have splatting for swift4.

But if we consider the type system as a guide, we can consider 3 simple
set of rules and restore almost 100% source compatibility while keeping the
improvement of SE-0110
- Rules for swift3 tuples-arguments of cardinality zero (Void) in swift
4 (this proposition)
- Rules for swift3 tuples-arguments of cardinality one in swift 4
(proposition to be done)
- Rules for swift3 tuples-arguments of cardinality > 1 in swift 4
(proposition to be done)

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 19:25:31, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

Unfortunately, I think this proposal appears to be mistaken as to this
key premise: Void was never (IIUC) meant to model the absence of arguments;
it is a type with one possible value.

If I recall, a number of conversations have been raised about Void being
a typealias of (), and the definitive response has been that this falls
into the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a
particular coding style have to do with loss of implicit tuple splatting,
the cure for which is a proper implementation of tuple splatting, not
poking holes into settled parts of the type system.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution < >>> swift-evolution@swift.org> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution < >>>> swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about
tuples usage.

After documenting myself about the changes which happened, I thought
that they could be improved. Instead of fighting these propositions (which
make sense), I wanted create a few proposal which would improve these
recent changes with a few simple rules.

My propositions are based on the recent decisions and in the
continuation of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason
of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not
parameters. I'm not sure there was ever much point in writing Void in a
parameter list, but whatever reasons there were surely vanished with
SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI
gave it a new purpose it with void*, but the meaning is totally unrelated.

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

[xwu (Xiaodi Wu)]

—
very short reply expected - vsre.info
Jérémie Girault

I invite you to read the proposal rules again with a fresh mindset and
benevolence spirit.
It’s my first one and may not be very clear but the rules are
straightforward.

Especially try to forget that Void is a tuple or anything.
Void is Nothing in the programmer’s mind. An instance of Void shouldn’t
even exist.

Sorry, that's not correct. Void is what's called Unit in other languages.
It exists. That is why functions with "no return value" return Void. OTOH,
Never does not exist. This discussion was had in great detail during the
naming debate over Never.

Let’s put facts in front of correctness assertions. Is Void = Unit in C or
c++ ? can you create instances of void in java ? you have Void for
generics. Unit type - Wikipedia

Sorry, I don't understand your line of argumentation. Fact: in Swift, Void
is the name of the unit type. Are you objecting to the naming of the unit
type in Swift? Do you want the unit type to have other features? Is there
some other way of modeling the unit type other than a tuple of arity 0 that
you prefer?

And if you look at assembly, sending void or returning void actually means
"nothing to push on the stack / nothing to pop”. Seems like having this
stripping on signatures at compile-time could be great !

Actually, in my opinion we could discuss naming when we agree that the
mechanism works, using this name is just a way to not impact the developer
with code changes.

So either we agree on the fact that the mechanism works and we can move on
to naming, or we get back on the topic : do you see a flaw in the proposal
rules ? It elegantly transforms signature arity and provides the programmer
a natural syntax to express it’s code.

I have read your proposal three times, but I do not understand what it is
proposing, in part because your proposal contains factual errors in the
premises. For instance, it claims repeatedly that Void is a typealias for
() because of something to do with argument lists, which is not true. It is
therefore unclear to me what it is you are proposing to do and what is
motivating such a proposal.

All I am saying is that, in previous conversations on this list, people who
actually do the work of implementing features in the compiler have stated
that `typealias Void = ()` is a fait accompli. With that as a starting
point, what do you propose to do?

···

On Mon, Jun 12, 2017 at 4:10 PM, Jérémie Girault <jeremie.girault@gmail.com> wrote:

On 12 juin 2017 at 22:34:45, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:
On Mon, Jun 12, 2017 at 3:16 PM, Jérémie Girault <jeremie.girault@ > gmail.com> wrote:

The proposed meaning of Void is to be a “lack” of arguments. It means
that each “Void” argument reduces the arity of the function by one, at its
exact position. Especially look at the canonical signature definition, and
the proposed rules of reduction.

I don't understand why you propose to name this new idea "Void". You're
proposing something that's not even a lack of an argument, but an
anti-argument, like anti-matter! I'm not sure I understand why this is
necessary. It seems to be a very strange workaround for one specific issue
arising from disallowing implicit tuple splatting.

Look at other languages, when you put Void in functions in C or java, do
you need to add a value ? Ease of use is important.

You imply that I disagree with splatting were I don’t, let’s not make it
personal. This proposal is even compatible with tuple splatting !

The proposal rules seem to work and provides great user value. Let’s try
to consider this !

That proposal, if implemented, would effectively allow `Callback<Void>`
to be called without arguments in the context of swift4.

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 22:06:54, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:56 PM, Jérémie Girault <jeremie.girault@ >> gmail.com> wrote:

@Xiaodi Wu
Disagree, and we would need the original designer here to help us, but
my understanding of the original meaning of tuples-as-arguments is that
when I define:
`func foo(_ arg0: Any, _ arg1: Any) {}`
I can afterwards “apply” a tuple to a function named `foo` and therefore
execute the function on this tuple.
Calling a function syntax was equivalent to put a tuple next to a
function name:
`foo(42, “hello")` the left-hand is `foo`, the right-hand is `(42,
“hello")` is the tuple.

The same way if I have
`func foo()`
`foo()` means calling `foo` with argument `()` and there we have our
original `Void`

That meaning changed recently due to multiple SE implementations
actually.

Tuples-as-arguments never shipped in any version of Swift, and the
ability to "apply" a tuple like that was removed by SE-0029--the original
goal was to implement this change in time for Swift 2.2.

The parenthesis around the call don't have a tuple meaning anymore.
Therefore it breaks a lot of code relying on this feature of the language,
which was quite elegant, but could not handle advanced functions features.

Yes, this is an intentional and approved part of SE-0029. The drawbacks
were enumerated in that proposal and were deemed acceptable.

@john: Void can happen easily in parameters due to generics, the easiest
example that breaks with swift4 is
`typealias Callback<T> = (T) -> Void`
here
`Callback<Void>` which is perfectly reasonable introduces Void in the
argument list and forces the caller to introduces an empty partenthesis set
when invoking:

let foo: Callback<Void> = { }
foo(())

`Callback<T> = (T) -> Void` refers to a callback that takes exactly one
argument. Since argument lists are not tuples, it is not possible to invoke
such a callback with zero arguments, or for that matter with two, three,
four, or five arguments.

That’s were the proposal shines in my opinion: adapting the meaning of

Void to the current context of swift4 gives back the language the elegant
syntax it had while preserving the type system

I'm not sure what you mean by this. No change in `Void` can cause a
function of type (T) -> Void to accept zero arguments: it requires one
argument of type T.

On 12 juin 2017 at 20:04:18, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 12:44 Jérémie Girault <jeremie.girault@gmail.com> >>> wrote:

Void was the empty tuple because arguments were tuples.

As John explained, that is _not_ correct. Void was not motivated by
anything to do with argument lists.

So no arguments meant empty tuple.

If we consider the empty tuple to be an argument, then the type for the
type of empty tuple should be `Unit`

It has been suggested to rename Void to Unit. I do believe it’s on the
commonly rejected ideas list (and if it’s not, it ought to be).

Void, however, seem naturally fitted for the absence of argument.

Should `func foo(Void)` be different from `func foo()`?

SE-0110 determined that the two should in fact be different.

I don’t think so. But different from `func foo(Unit)` ? Yes !

It sounds like your quarrel is with the name of the typealias. I don’t
see how that solves any issues with the loss of tuple splatting. Functions
will still return (), and you foo(()) is not foo().

My point here is that we probably won’t have splatting for swift4.

But if we consider the type system as a guide, we can consider 3 simple
set of rules and restore almost 100% source compatibility while keeping the
improvement of SE-0110
- Rules for swift3 tuples-arguments of cardinality zero (Void) in swift
4 (this proposition)
- Rules for swift3 tuples-arguments of cardinality one in swift 4
(proposition to be done)
- Rules for swift3 tuples-arguments of cardinality > 1 in swift 4
(proposition to be done)

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 19:25:31, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

Unfortunately, I think this proposal appears to be mistaken as to this
key premise: Void was never (IIUC) meant to model the absence of arguments;
it is a type with one possible value.

If I recall, a number of conversations have been raised about Void
being a typealias of (), and the definitive response has been that this
falls into the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a
particular coding style have to do with loss of implicit tuple splatting,
the cure for which is a proper implementation of tuple splatting, not
poking holes into settled parts of the type system.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution < >>>> swift-evolution@swift.org> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution < >>>>> swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about
tuples usage.

After documenting myself about the changes which happened, I thought
that they could be improved. Instead of fighting these propositions (which
make sense), I wanted create a few proposal which would improve these
recent changes with a few simple rules.

My propositions are based on the recent decisions and in the
continuation of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The
reason of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not
parameters. I'm not sure there was ever much point in writing Void in a
parameter list, but whatever reasons there were surely vanished with
SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI
gave it a new purpose it with void*, but the meaning is totally unrelated.

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

[xwu (Xiaodi Wu)]

—
very short reply expected - vsre.info
Jérémie Girault

- Void as arguments is pretty common when using generics, that’s a core
point of this proposal. An maybe that’s why we misunderstood ourselves
(around 0110 / 0066). This proposal addresses arguments.
- maybe it should be revised around this ? Simple example :

`typealias Callback<T> = (T) -> Void` -> `Callback<Void>` will give
`(Void) => Void`.

It was acceptable before swift4 but no more. However nobody cares about
this `Void` argument and actually we know it’s value. So why let the
developer type it ?

Ah, I see. The purpose of SE-0029...SE-0110 was to make it possible to
distinguish an argument list `(Void)` from an argument list `()`. This does
cause some verbosity where previously users relied on implicit tuple
splatting. Ideally, we would bring back some syntactic sugar to make this
more ergonomic. But, whether or not the spelling is made more
user-friendly, the point here is that _everybody_ should care about this
`Void` argument.

It is still be typechecked and appropriate errors should be reported to
the user so _nobody_ will ignore it.

But with the proposal the code will be striped out of Void arguments at
compile-time. I think it's a win for the developer on a lot of grounds. The
fact that this proposal integrates with the type-system is also important.

If you are not comfortable about Void being stripped, we can also discuss
alternatives: someone was suggesting me that it would be possible to
replace :

func foo<T, U, V>(t: T, u: U) -> V {

  // do something with t and u

  // return some V

}

with

func foo<Void, Int, String>(u: Int) -> String { let t = ()

  // do something with t and u

  // return some V

}

or

func foo<Void, Int, String>(t: Void = (), u: Int) -> String {

  // do something with t and u

  // return some V

}

I don’t know what you would consider more effective or elegant (at an
implementation level) but it’s the same result for the developper.

What is the goal of such changes? Is it to allow you to write `foo()`
instead of `foo(())` for a function `foo` of type `(T) -> Void`?

If so, then I think what you're seeking to do is reverse SE-0066 (as
Vladimir points out), which explicits details how it's is an intentional
change to require such a spelling. I think you're starting from the premise
that this is unintended or undesirable, when in fact it is deliberate and
approved.

It is also, unless I'm mistaken, not the issue that was raised initially
with respect to SE-0110, which had to do with the extra boilerplate of
destructuring a tuple inside a closure, something that was not so obvious
before implementation.

My point here is that `Void` should be “striped” by “reducing” argument

···

On Mon, Jun 12, 2017 at 5:25 PM, Jérémie Girault <jeremie.girault@gmail.com> wrote:

On 12 juin 2017 at 23:56:37, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:
On Mon, Jun 12, 2017 at 4:47 PM, Jérémie Girault <jeremie.girault@gmail > .com> wrote:

list signatures.

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 19:15:18, John McCall (rjmccall@apple.com) wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution < >> swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about
tuples usage.

After documenting myself about the changes which happened, I thought that
they could be improved. Instead of fighting these propositions (which make
sense), I wanted create a few proposal which would improve these recent
changes with a few simple rules.

My propositions are based on the recent decisions and in the continuation
of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason
of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not parameters.
I'm not sure there was ever much point in writing Void in a parameter list,
but whatever reasons there were surely vanished with SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI
gave it a new purpose it with void*, but the meaning is totally unrelated.

John.

[Jens]

Just adding this here for reference:
func foo(_: Void) {}
func bar() {}
// All these compile in Swift 3:
foo()
foo(())
bar()
bar(())
// But only these two compile in Swift 4:
foo(())
bar()

···

On Mon, Jun 12, 2017 at 9:44 PM, Xiaodi Wu via swift-evolution < swift-evolution@swift.org> wrote:

On Mon, Jun 12, 2017 at 2:32 PM, Jérémie Girault < > jeremie.girault@gmail.com> wrote:

@xiaodi
I disagree on many points, for example what is the type of x when we type
`let x = *Void` ?

That would not be a legal statement. Exploding a tuple is an operation
that only makes sense inside an argument list. Likewise `let x = &Void`
will not compile.

This is the essence of the problem and this proposition wants to solve
this.

The regression is due to both reason combined : typealias Void = () AND
SE-0110

My proposition is to change the meaning of Void from () to “something
else” that is type-compatible with SE-0110 (and splatting in the future).

I'm not sure I understand your motivation. Void is just a typealias. If
tomorrow Void meant something else, all functions must still return (), and
there is still no implicit tuple splatting.

If you want an example of the changes needed to migrate to swift4, just
look at the 42 files of handling parenthesis PR of RxSwift needed for
swift4 upgrade : Compile under Swift 4 by volodg · Pull Request #1282 · ReactiveX/RxSwift · GitHub

Indeed, that's the result of SE-0110; these parentheses are needed because
there is no implicit tuple splatting. They would be required even if `Void`
did not exist in the language at all.

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 21:18:06, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:05 PM, David Hart <david@hartbit.com> wrote:

On 12 Jun 2017, at 19:25, Xiaodi Wu via swift-evolution < >>> swift-evolution@swift.org> wrote:

Unfortunately, I think this proposal appears to be mistaken as to this
key premise: Void was never (IIUC) meant to model the absence of arguments;
it is a type with one possible value.

If I recall, a number of conversations have been raised about Void being
a typealias of (), and the definitive response has been that this falls
into the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a
particular coding style have to do with loss of implicit tuple splatting,
the cure for which is a proper implementation of tuple splatting, not
poking holes into settled parts of the type system.

But you can’t deny that SE-0110 has also caused regressions in the use
of Void as generic argument because Void is modelled as the empty tuple.

I'm not sure I understand this statement. Void is a synonym for the empty
tuple, and that hasn't ever changed, so it can't be the root cause of any
regressions.

And tuple splatting will not fix those regressions.

How come? If `*` is the splat operator, then it would be legal to call a
function `foo` that takes no arguments with `foo(*Void)`; if implicit tuple
splatting returns in fully implemented form, then it would be legal to call
it once again with `foo(Void)`.

And contrary to what some people might think, this is not an “edge-case”.

Most useful monads modelled with generics have good reasons to use Void:

*The Result<T> monad:* Result<Void> represents the result of an
operation with no return value
*The Promise<T> monad:* Promise<Void> represents the result of an
asynchronous operation with no return value
*The Observable<T> monad (in functional reactive programming):*
Observable<Void> represents a stream of events with no values

I use all three monads in my code and I’ve had to modify a lot of code
when migrating to Swift 4 beta1 because of Void.

Can you give examples of the modifications needed during migration? From
here, I can only see that the reason any code needs modification is the
complete removal of implicit tuple splatting. Nothing has changed about
Void being a synonym for the empty tuple; even if you rename Void,
functions will still return () by some other name, and unless there is
tuple splatting in some form, the migration you performed is inevitable.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution < >>> swift-evolution@swift.org> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution < >>>> swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about
tuples usage.

After documenting myself about the changes which happened, I thought
that they could be improved. Instead of fighting these propositions (which
make sense), I wanted create a few proposal which would improve these
recent changes with a few simple rules.

My propositions are based on the recent decisions and in the
continuation of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason
of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not
parameters. I'm not sure there was ever much point in writing Void in a
parameter list, but whatever reasons there were surely vanished with
SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI
gave it a new purpose it with void*, but the meaning is totally unrelated.

John.
_______________________________________________
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

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

[Jens]

I think this proposal would be complicating rather than simplifying the
type system, it would be adding a special rule.
And it is not a step towards resolving the many parentheses-related
inconsistencies that still remain.

Here is an example of one such remaining inconsistency, it's still in
(latest dev snapshot) Swift 4, so this is the behavior of both Swift 3(.2)
and 4:
func foo() -> Void {}
func foo(_: Void) -> Void {} // This is OK
func bar(fn: () -> Void) {}
func bar(fn: (_: Void) -> Void) {} // ERR: Invalid redecl.

I think the least surprising behavior here would be no error, rather than
two.
The current behavior with one error is very surprising.

···

On Mon, Jun 12, 2017 at 10:09 PM, Xiaodi Wu via swift-evolution < swift-evolution@swift.org> wrote:

On Mon, Jun 12, 2017 at 3:04 PM, Jérémie Girault < > jeremie.girault@gmail.com> wrote:

Exactly, that means that your implementation of the tuple splatting
operator is out of the type system.
Can you expose it’s signature ?

If you want the operator to be “compiler-magic” it’s possible.

Yes, it requires compiler support.

This proposal is an alternate solution.

My point is that updating Void according to this proposal would
- preserve the type system in a better way
- have better source compatibility (in time for swift 4 release, were we
probably won’t see tuple splatting)
- also keep the elegant original syntax of swift instead of stacking
parenthesis

The impact for code writers would be minimized on time for swift 4 release

As for return values: this proposition does not intend to change the how
return value of Void functions works.

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 21:45:08, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:32 PM, Jérémie Girault <jeremie.girault@gmail >> .com> wrote:

@xiaodi
I disagree on many points, for example what is the type of x when we
type `let x = *Void` ?

That would not be a legal statement. Exploding a tuple is an operation
that only makes sense inside an argument list. Likewise `let x = &Void`
will not compile.

This is the essence of the problem and this proposition wants to solve
this.

The regression is due to both reason combined : typealias Void = () AND
SE-0110

My proposition is to change the meaning of Void from () to “something
else” that is type-compatible with SE-0110 (and splatting in the future).

I'm not sure I understand your motivation. Void is just a typealias. If
tomorrow Void meant something else, all functions must still return (), and
there is still no implicit tuple splatting.

If you want an example of the changes needed to migrate to swift4, just
look at the 42 files of handling parenthesis PR of RxSwift needed for
swift4 upgrade : Compile under Swift 4 by volodg · Pull Request #1282 · ReactiveX/RxSwift · GitHub

Indeed, that's the result of SE-0110; these parentheses are needed
because there is no implicit tuple splatting. They would be required even
if `Void` did not exist in the language at all.

—
very short reply expected - vsre.info
Jérémie Girault

On 12 juin 2017 at 21:18:06, Xiaodi Wu (xiaodi.wu@gmail.com) wrote:

On Mon, Jun 12, 2017 at 2:05 PM, David Hart <david@hartbit.com> wrote:

On 12 Jun 2017, at 19:25, Xiaodi Wu via swift-evolution < >>>> swift-evolution@swift.org> wrote:

Unfortunately, I think this proposal appears to be mistaken as to this
key premise: Void was never (IIUC) meant to model the absence of arguments;
it is a type with one possible value.

If I recall, a number of conversations have been raised about Void
being a typealias of (), and the definitive response has been that this
falls into the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a
particular coding style have to do with loss of implicit tuple splatting,
the cure for which is a proper implementation of tuple splatting, not
poking holes into settled parts of the type system.

But you can’t deny that SE-0110 has also caused regressions in the use
of Void as generic argument because Void is modelled as the empty tuple.

I'm not sure I understand this statement. Void is a synonym for the
empty tuple, and that hasn't ever changed, so it can't be the root cause of
any regressions.

And tuple splatting will not fix those regressions.

How come? If `*` is the splat operator, then it would be legal to call a
function `foo` that takes no arguments with `foo(*Void)`; if implicit tuple
splatting returns in fully implemented form, then it would be legal to call
it once again with `foo(Void)`.

And contrary to what some people might think, this is not an

“edge-case”. Most useful monads modelled with generics have good reasons to
use Void:

*The Result<T> monad:* Result<Void> represents the result of an
operation with no return value
*The Promise<T> monad:* Promise<Void> represents the result of an
asynchronous operation with no return value
*The Observable<T> monad (in functional reactive programming):* Observable<Void>
represents a stream of events with no values

I use all three monads in my code and I’ve had to modify a lot of code
when migrating to Swift 4 beta1 because of Void.

Can you give examples of the modifications needed during migration? From
here, I can only see that the reason any code needs modification is the
complete removal of implicit tuple splatting. Nothing has changed about
Void being a synonym for the empty tuple; even if you rename Void,
functions will still return () by some other name, and unless there is
tuple splatting in some form, the migration you performed is inevitable.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution < >>>> swift-evolution@swift.org> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution < >>>>> swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about
tuples usage.

After documenting myself about the changes which happened, I thought
that they could be improved. Instead of fighting these propositions (which
make sense), I wanted create a few proposal which would improve these
recent changes with a few simple rules.

My propositions are based on the recent decisions and in the
continuation of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The
reason of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not
parameters. I'm not sure there was ever much point in writing Void in a
parameter list, but whatever reasons there were surely vanished with
SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI
gave it a new purpose it with void*, but the meaning is totally unrelated.

John.
_______________________________________________
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

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

[VladimirS (Vladimir)]

    Void was the empty tuple because arguments were tuples.

As John explained, that is _not_ correct. Void was not motivated by anything to do with argument lists.

    So no arguments meant empty tuple.

    If we consider the empty tuple to be an argument, then the type for the type of
    empty tuple should be `Unit`

It has been suggested to rename Void to Unit. I do believe it’s on the commonly rejected ideas list (and if it’s not, it ought to be).

    Void, however, seem naturally fitted for the absence of argument.

    Should `func foo(Void)` be different from `func foo()`?

SE-0110 determined that the two should in fact be different.

Actually *SE-0066* determinate this first:

(code example in *Proposed solution* section)

let f: () -> Int // function with no parameters
let g: (()) -> Int // function taking a single () parameter
let h: ((())) -> Int // function taking a single () parameter

f(); g(()); h(()) // correct
f(()); g(); h() // errors

Seems like it's just SE-0066 *more correctly* implemented in Swift 4 *in addition* to SE-0110 implementation.

···

On 12.06.2017 21:04, Xiaodi Wu via swift-evolution wrote:

On Mon, Jun 12, 2017 at 12:44 Jérémie Girault <jeremie.girault@gmail.com > <mailto:jeremie.girault@gmail.com>> wrote:

    I don’t think so. But different from `func foo(Unit)` ? Yes !

It sounds like your quarrel is with the name of the typealias. I don’t see how that solves any issues with the loss of tuple splatting. Functions will still return (), and you foo(()) is not foo().

    My point here is that we probably won’t have splatting for swift4.

    But if we consider the type system as a guide, we can consider 3 simple set of
    rules and restore almost 100% source compatibility while keeping the improvement
    of SE-0110
    - Rules for swift3 tuples-arguments of cardinality zero (Void) in swift 4 (this
    proposition)
    - Rules for swift3 tuples-arguments of cardinality one in swift 4 (proposition to
    be done)
    - Rules for swift3 tuples-arguments of cardinality > 1 in swift 4 (proposition to
    be done)

    —
    very short reply expected - vsre.info <http://vsre.info>
    Jérémie Girault

    On 12 juin 2017 at 19:25:31, Xiaodi Wu (xiaodi.wu@gmail.com > <mailto:xiaodi.wu@gmail.com>) wrote:

    Unfortunately, I think this proposal appears to be mistaken as to this key
    premise: Void was never (IIUC) meant to model the absence of arguments; it is a
    type with one possible value.

    If I recall, a number of conversations have been raised about Void being a
    typealias of (), and the definitive response has been that this falls into the
    ship-has-sailed category of out-of-scope changes.

    More generally, the recent spate of complaints about regressions to a
    particular coding style have to do with loss of implicit tuple splatting, the
    cure for which is a proper implementation of tuple splatting, not poking holes
    into settled parts of the type system.

    On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution >> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

        On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution >>> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:

        Hi here,

        As I tested swift4 in xcode9b1 I noticed a lot of regressions about tuples
        usage.

        After documenting myself about the changes which happened, I thought that
        they could be improved. Instead of fighting these propositions (which make
        sense), I wanted create a few proposal which would improve these recent
        changes with a few simple rules.

        My propositions are based on the recent decisions and in the continuation
        of SE-0110. The first one is about Void.
        Void is historically defined as the type of the empty tuple. The reason of
        this is that arguments were initially considered as tuple.

        The dominant consideration here was always return types, not parameters. I'm not sure there was ever much point in writing Void in a parameter list,
        but whatever reasons there were surely vanished with SE-0066.

        Note that 'void' in C was originally exclusively a return type. ANSI gave
        it a new purpose it with void*, but the meaning is totally unrelated.

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

[Anders]

Just want to note that `Void` aka empty tuple is still constructible, so it doesn’t exactly mean “no value” but only “an occurrence without a substantial value”, especially when a stream of voids in FRP can be used as a trigger.

To exactly represent “no value”, inhabitable types like `Never` are better as they statically guarantee that no instance would ever exist.

Regards,
Anders

···

On 13 Jun 2017, at 3:05 AM, David Hart via swift-evolution <swift-evolution@swift.org> wrote:

On 12 Jun 2017, at 19:25, Xiaodi Wu via swift-evolution <swift-evolution@swift.org> wrote:

Unfortunately, I think this proposal appears to be mistaken as to this key premise: Void was never (IIUC) meant to model the absence of arguments; it is a type with one possible value.

If I recall, a number of conversations have been raised about Void being a typealias of (), and the definitive response has been that this falls into the ship-has-sailed category of out-of-scope changes.

More generally, the recent spate of complaints about regressions to a particular coding style have to do with loss of implicit tuple splatting, the cure for which is a proper implementation of tuple splatting, not poking holes into settled parts of the type system.

But you can’t deny that SE-0110 has also caused regressions in the use of Void as generic argument because Void is modelled as the empty tuple. And tuple splatting will not fix those regressions.

And contrary to what some people might think, this is not an “edge-case”. Most useful monads modelled with generics have good reasons to use Void:

The Result<T> monad: Result<Void> represents the result of an operation with no return value
The Promise<T> monad: Promise<Void> represents the result of an asynchronous operation with no return value
The Observable<T> monad (in functional reactive programming): Observable<Void> represents a stream of events with no values

I use all three monads in my code and I’ve had to modify a lot of code when migrating to Swift 4 beta1 because of Void.

David.

On Mon, Jun 12, 2017 at 12:15 John McCall via swift-evolution <swift-evolution@swift.org> wrote:

On Jun 12, 2017, at 4:48 AM, Jérémie Girault via swift-evolution <swift-evolution@swift.org> wrote:

Hi here,

As I tested swift4 in xcode9b1 I noticed a lot of regressions about tuples usage.

After documenting myself about the changes which happened, I thought that they could be improved. Instead of fighting these propositions (which make sense), I wanted create a few proposal which would improve these recent changes with a few simple rules.

My propositions are based on the recent decisions and in the continuation of SE-0110. The first one is about Void.
Void is historically defined as the type of the empty tuple. The reason of this is that arguments were initially considered as tuple.

The dominant consideration here was always return types, not parameters. I'm not sure there was ever much point in writing Void in a parameter list, but whatever reasons there were surely vanished with SE-0066.

Note that 'void' in C was originally exclusively a return type. ANSI gave it a new purpose it with void*, but the meaning is totally unrelated.

John.
_______________________________________________
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

_______________________________________________
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