[swift-evolution] Revisiting SE-0110

[Nevin Brackett-Rozinsky]

On Mon, May 29, 2017 at 3:18 PM, Vladimir.S <svabox at gmail.com> wrote:

> On 29.05.2017 21:08, Nevin Brackett-Rozinsky wrote:
>>
>> barTuple{ (x, y) in }   // valid, destructuring one tuple
>> barTuple{ ((x, y)) in } // valid, destructuring one tuple with optional
>> parentheses
>>
>
> Here is the problem for me. According to SE-0066 closure declared as
> {(x,y) in} should be of type (Int,Int)->() and not ((Int,Int))->().
> Why do you want to be able to pass wrong function/closure type into
> barTuple?


 I don’t.

I want the compile to infer from context whether “{ (x, y) in }” is of type
“(_, _) -> _” with the optional parentheses included, or of type “((_, _))
-> _” with the optional parentheses elided. This is similar to how we use
context to determine whether “1” is of type Int or Double or something else
entirely.

If a closure appears in a context where it can only accept a tuple, such as
mapping a dictionary, then obviously its type should have a tuple
parameter. If a closure appears in a context where it can only accept two
arguments, then obviously its type should have two parameters.

I want the compiler to figure out, when possible from context, whether the
optional parentheses were included, so it “just works” for developers.

Nevin
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