[swift-evolution] Revisiting SE-0110
Tommaso Piazza
tommy.piazza at ymail.com
Fri Jun 2 14:25:44 CDT 2017
Thanks, added.
On Friday, June 2, 2017 1:18 PM, Vladimir.S <svabox at gmail.com> wrote:
On 02.06.2017 2:34, Tommaso Piazza wrote:
> Is the version you suggest to add to my list for the Swift syntax currently valid as
> of SE-0110 in Swift 4?
Yes, just checked on latest dev snapshot of Swift 4.
>
>
> On Thursday, June 1, 2017 9:32 PM, Vladimir.S <svabox at gmail.com> wrote:
>
>
> On 01.06.2017 19:31, Tommaso Piazza wrote:
> > Dear all,
> >
> > I made a comparison of Swift's 4 lack of tuple unsplatting, here is how it stands in
> > comparison with other languages
> >
> > https://gist.github.com/blender/53f9568617654c38a219dd4a8353d935
> >
>
> Thank you! Very useful information. And also I really like the opinion of
> @AliSoftware in comments for this article.
>
> I'd suggest to add this variant to Swift section in your article:
>
> let eighteenOrMore = ["Tom" : 33, "Rebecca" : 17, "Siri" : 5].filter {
> (arg: (name: String, age: Int)) in arg.age >= 18 }
>
> (I believe it is better that 2 others Swift variants.)
>
> It seems for me that we need to allow some special syntax for *explicit* tuple
> destructuring in closures to make all happy.
>
> FWIW These suggestions are my favorite:
>
> 1. Just allow type inference for tuple's destructured variables in this position:
>
> .filter { (arg: (name, age)) in arg.age >= 18 }
>
>
> 2. (1) + allow underscore for tuple argument name:
>
> .filter { (_: (name, age)) in age >= 18 }
>
>
> 3. (2) + allow to omit parenthesis (probably only in case of just one tuple argument)
>
> .filter { _: (name, age) in age >= 18 }
>
>
> 4. Use pattern matching syntax:
>
> .filter { case let (name, age) in age >= 18 }
>
> (looks similar as allowed today: if case let (name, age) = x { print(name, age) } )
>
>
> 5. Use two pairs of parenthesis :
>
> .filter { ((name, age)) in age >= 18 }
>
> Btw, about the 5th variant. If took what is allowed today:
> .filter { (arg: (name: String, age: Int)) in arg.age >= 18 }
> , and allow type inference for tuple part arguments, we'll have this:
> .filter { (arg: (name, age)) in arg.age >= 18 }
> , and if additionally allow skipping of tuple argument declaration we'll have:
> .filter { ((name, age)) in arg.age >= 18 }
> I.e. two pairs for parenthesis for tuple destructuring, and such syntax is similar to
> the type this closure should have : ((String, Int)) -> Bool
>
>
> >
> >
> >
> > On Thursday, June 1, 2017 12:25 PM, Vladimir.S via swift-evolution
> > <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> >
> >
> > On 01.06.2017 0:42, John McCall wrote:
> > >> On May 31, 2017, at 2:02 PM, Stephen Celis <stephen.celis at gmail.com
> <mailto:stephen.celis at gmail.com>
> > <mailto:stephen.celis at gmail.com <mailto:stephen.celis at gmail.com>>> wrote:
> > >>> On May 28, 2017, at 7:04 PM, John McCall via swift-evolution
> > >>> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>
> <mailto:swift-evolution at swift.org <mailto:swift-evolution at swift.org>>> wrote:
> > >>>
> > >>> Yes, I agree. We need to add back tuple destructuring in closure parameter
> > >>> lists because this is a serious usability regression. If we're reluctant to
> > >>> just "do the right thing" to handle the ambiguity of (a,b), we should at least
> > >>> allow it via unambiguous syntax like ((a,b)). I do think that we should just
> > >>> "do the right thing", however, with my biggest concern being whether there's
> > >>> any reasonable way to achieve that in 4.0.
> > >>
> > >> Closure parameter lists are unfortunately only half of the equation here. This
> > >> change also regresses the usability of point-free expression.
> > >
> > > The consequences for point-free style were expected and cannot really be
> > > eliminated without substantially weakening SE-0110. Closure convenience seems to
> > > me to be a much more serious regression.
> >
> > John, do you also want to say "and without weakening SE-0066"? Because, if I
> > understand correctly, in this case:
> >
> > func add(_ x: Int, _ y: Int) -> Int {
> > return x + y
> > }
> >
> > zip([1, 2, 3], [4, 5, 6]).map(add)
> >
> > .. we have a clear function type mismatch situation, when map() expects function of
> > type ((Int, Int))->Int, but function of type (Int,Int)->Int is provided ? So probably
> > the additional 'reason' of the 'problem' in this case is SE-0066, no?
> > Or I don't understand the SE-0066 correctly..
> > Do we want to allow implicit conversions between function type ((Int,Int))->Int and
> > (Int,Int)->Int?
> >
> > Quote from SE-0066:
> > ---
> > (Int, Int) -> Int // function from Int and Int to Int
> > ((Int, Int)) -> Int // function from tuple (Int, Int) to Int
> > ---
> >
> > During this discussion I see a wish of some group of developers to just return back
> > tuple splatting for function/closure arguments, so they can freely send tuple to
> > function/closure accepting a list of parameters(and probably vise-versa).
> > Is it worth to follow SE-0066 and SE-0110 as is, i.e. disallow tuple deconstructing
> > and then, as additive change improve the situation with tuple
> > splatting/deconstructing later with separate big proposal?
> >
> > Btw, about the SE-0110 proposal. It was discussed, formally reviewed and accepted. I
> > expect that its revision also should be formally proposed/reviewed/accepted to
> > collect a wide range of opinions and thoughts, and attract the attention of
> > developers in this list to the subject.
> >
> >
> > Also, if we revisit SE-0110, will this code be allowed?:
> >
> > func foo(_ callback: ((Int,Int))->Void) {}
> > let mycallback = {(x:Int, y:Int)->Void in }
> > foo(mycallback)
> >
> > and
> >
> > func foo(_ callback: (Int,Int)->Void) {}
> > let mycallback = {(x: (Int, Int))->Void in }
> > foo(mycallback)
> >
> > If so, what will be result of this for both cases? :
> >
> > print(type(of:mycallback)) // (Int,Int)->Void or ((Int,Int))->Void
> >
> > If allowed, do we want to allow implicit conversion between types (Int,Int)->Void and
> > ((Int,Int))->Void in both directions? (Hello tuple splatting?)
> >
> >
> > >
> > > John.
> > >
> > >
> > >>
> > >> func add(_ x: Int, _ y: Int) -> Int { return x + y }
> > >>
> > >> zip([1, 2, 3], [4, 5, 6]).map(add)
> > >>
> > >> // error: nested tuple parameter '(Int, Int)' of function '(((_.Element,
> > >> _.Element)) throws -> _) throws -> [_]' does not support destructuring
> > >>
> > >> This may not be a common pattern in most projects, but we heavily use this style
> > >> in the Kickstarter app in our functional and FRP code. Definitely not the most
> > >> common coding pattern, but a very expressive one that we rely on.
> > >>
> > >> Our interim solution is a bunch of overloaded helpers, e.g.:
> > >>
> > >> func tupleUp<A, B, C>(_ f: (A, B) -> C) -> ((A, B)) -> C { return }
> > >>
> > >> zip([1, 2, 3], [4, 5, 6]).map(tupleUp(add))
> > >>
> > >> Stephen
> > >
> > > .
> > >
> > _______________________________________________
> > swift-evolution mailing list
> > swift-evolution at swift.org <mailto:swift-evolution at swift.org>
> <mailto:swift-evolution at swift.org <mailto:swift-evolution at swift.org>>
>
> > https://lists.swift.org/mailman/listinfo/swift-evolution
> >
> >
>
>
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