[swift-evolution] Proposal: Always flatten the single element tuple

[Gwendal Roué]

> Le 7 juin 2017 à 12:33, Gwendal Roué <gwendal.roue at gmail.com> a écrit :
> 
> 
>> Le 7 juin 2017 à 12:03, Adrian Zubarev via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> a écrit :
>> 
>> Well please no:
>> 
>> 
>>  let fn2: ((Int, Int)) -> Void = { lhs, rhs in } 
>> 
>> Instead use destructuring sugar pitched by Chris Lattner on the other thread:
>> 
>> let fn2: ((Int, Int)) -> Void = { ((lhs, rhs)) in }
>> 
> 
> Despite Chris Lattern being a semi-god, his double-parenthesis suggestion cruelly lacks in terms of user ergonomics. The compiler should be able to deal with the following code snippet, just like Swift 3 does:
> 
>     // two arguments
>     func f1(_ closure: (Int, Int) -> Int) { closure(1, 2) }
> [...]

Here is the full extent of the remarquable Swift 3 ergonomics. This full snippet compiles in Swift 3:

    func sum1(_ lhs: Int, _ rhs: Int) -> Int { return lhs + rhs }
    func sum2(lhs: Int, rhs: Int) -> Int { return lhs + rhs }
    func sum3(tuple: (Int, Int)) -> Int { return tuple.0 + tuple.1 }
    func sum4(tuple: (lhs: Int, rhs: Int)) -> Int { return tuple.lhs + tuple.rhs }

    // two arguments
    func f1(_ closure: (Int, Int) -> Int) { closure(1, 2) }
    f1 { lhs, rhs in lhs + rhs }
    f1 { (lhs, rhs) in lhs + rhs }
    f1 { tuple in tuple.0 + tuple.1 }
    f1 { (tuple) in tuple.0 + tuple.1 }
    f1(+)
    f1(sum1)
    f1(sum2)
    f1(sum3)
    f1(sum4)
    
    // two arguments, with documentation names: identical
    func f2(_ closure: (_ a: Int, _ b: Int) -> Int) { closure(1, 2) }
    f2 { lhs, rhs in lhs + rhs }
    f2 { (lhs, rhs) in lhs + rhs }
    f2 { tuple in tuple.0 + tuple.1 }
    f2 { (tuple) in tuple.0 + tuple.1 }
    f2(+)
    f2(sum1)
    f2(sum2)
    f2(sum3)
    f2(sum4)
    
    // one tuple argument
    func f3(_ closure: ((Int, Int)) -> Int) { closure((1, 2)) }
    f3 { lhs, rhs in lhs + rhs }
    f3 { (lhs, rhs) in lhs + rhs }
    f3 { tuple in tuple.0 + tuple.1 }
    f3 { (tuple) in tuple.0 + tuple.1 }
    f3(+)
    f3(sum1)
    f3(sum2)
    f3(sum3)
    f3(sum4)
    
    // one keyed tuple argument
    func f4(_ closure: ((a: Int, b: Int)) -> Int) { closure((a: 1, b: 2)) }
    f4 { lhs, rhs in lhs + rhs }
    f4 { (lhs, rhs) in lhs + rhs }
    f4 { tuple in tuple.a + tuple.b }
    f4 { (tuple) in tuple.a + tuple.b }
    f4(+)
    f4(sum1)
    f4(sum2)
    f4(sum3)
    f4(sum4)

Gwendal

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