Slava Pestov answered this question on Twitter.
He says it's a known bug and: "Right now, function types always have a
single parameter internally. Diff between a and b is lost after type check".
On Sat, Aug 27, 2016 at 6:28 PM, Jens Persson <j...@bitcycle.com> wrote:
> IMHO Swift's handling of function types violate the principle of least
> surprise.
>
> In the example program below, are `a` and `b` really of the same function
> type?
>
> I searched but couldn't find any proposal or discussion addressing this.
>
>
> // (Xcode 8 beta 6, toolchain: development snapshot 2016-08-26)
>
> let a: (Int, Int) -> Int = { (a, b) in a + b }
> let b: ((Int, Int)) -> Int = a
> // So `a` can be casted to `b`'s type, OK.
>
> print(type(of:a)) // ((Int, Int)) -> Int
> print(type(of:b)) // ((Int, Int)) -> Int
>
> // Why are they printed the same?
> // I would only expect `b`'s type to look like that.
> // Now it looks like both take a tuple of two Ints.
>
> let c = a( 1, 2 ) // Can only be called this way, as expected.
> let d = b((1, 2)) // Can only be called this way, as expected.
> print(c) // 3, as expected.
> print(d) // 3, as expected.
>
> print(type(of:a) == type(of:b)) // true
> // What? `a` clearly takes two Ints, while `b` clearly takes a
> // tuple of two Ints, yet they are the same type?
> // I am perplexed.
>
>
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