Currying requires external parameter, even though there is none

Originator:lucasderraugh
Number:rdar://17458161 Date Originated:
Status:Open Resolved:
Product:Developer Tools Product Version:
Classification: Reproducible:
 
Summary:
When currying a function, the external parameter is required in the case of the second parameter

Here's an example:

func add(x: Int)(y: Int) -> Int {return x+y}
let incrementBy2 = add(2)
let val = incrementBy2(10) // Error: requires 'y:' even though it's not an external parameter

To resolve this issue you can type:
let val = incrementBy2(y: 10)

But this makes no sense and it makes currying a rather useless feature when there has to be (potentially) arbitrary names attached to the parameters

Steps to Reproduce:
1. Run playground file (or code above)
2. Observe error (Missing argument label 'y:' in call)

Expected Results:
Not to have the need for the 'y:' as a parameter since it is not an external parameter

Actual Results:
Error: Missing argument label 'y:' in call

Version:
Xcode 6 Beta 2
Version 6.0 (6A216f)

Comments

Workaround

FWIW, you can work around this limitation by "manually currying" the function: 

let add: Int -> Int -> Int = { x in { y in x + y } }
let incrementBy2 = add(2)
let val = incrementBy2(10)

But it would be nice if Swift's currying syntax handled this.

By kristopherdjohnson at June 27, 2014, 6:25 p.m. (reply...)

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