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
<[email protected]> wrote:
On 01.06.2017 0:42, John McCall wrote:
>> On May 31, 2017, at 2:02 PM, Stephen Celis <[email protected]
<mailto:[email protected]>> wrote:
>>> On May 28, 2017, at 7:04 PM, John McCall via swift-evolution
>>> <[email protected] <mailto:[email protected]>> 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
>
> .
>
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