[swift-evolution] Revisiting SE-0110
Vladimir.S
svabox at gmail.com
Thu Jun 1 15:02:08 CDT 2017
On 01.06.2017 22:46, T.J. Usiyan wrote:
> I, for one, would be willing to accept Xiaodi's suggestion involving `let`–especially
> if (pipe dream follows) we could use the same syntax in functions/methods to
> destructure parameters.
Yes, Xiaodi's suggestion also was very attractive. Just to remind:
----------
{ (a, b) -> Int in } // two parameters
{ let (a, b) -> Int in } // destructuring one parameter
{ a, let (b, c) -> Int in } // destructuring two parameters
{ let a, (b, c) -> Int in } // still destructuring two parameters
{ let (a, (b, c)) -> Int in } // destructuring one parameter
{ (a, (b, c)) -> Int in } // error: add 'let' to destructure second parameter
----------
>
> On Thu, Jun 1, 2017 at 3:32 PM, Vladimir.S via swift-evolution
> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> 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
> <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
> <https://lists.swift.org/mailman/listinfo/swift-evolution>
>
>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org <mailto:swift-evolution at swift.org>
> https://lists.swift.org/mailman/listinfo/swift-evolution
> <https://lists.swift.org/mailman/listinfo/swift-evolution>
>
>
More information about the swift-evolution
mailing list