Is it possible to create an array of functions that take “inout” parameters in Swift?

Question

I am running into something that I think might be a bug. Swift lets you create an array of functions, like this:

func example1(a: Int) {
    println(a)
}

let functionArray1 = [example1]

println(functionArray1[0](3))      // This prints "3"

But if I try to create an array of functions that take an inout parameter, I get the dreaded segmentation fault 11 :

func example2(inout a: Int) {
    println(a)
}

let functionArray2 = [example2]  // This produces the seg fault

It makes no difference if I actually manipulate a inside the function or not.

Does anyone know what is going on here? Is there a way to create an array of functions with an inout parameter by using an appropriate type annotation, or some other trick?

EDIT: I have tried providing a type annotation for the array - that does not solve the problem:

let functionArray2: [(inout Int) -> ()] = [example2]   // Same error...

I have also tried writing the function as a closure (with an explicit type annotation) and then adding the closure to an array, also with no success.

Answer 1

As the comments on the question have pointed out, this does appear to be a bug relating to Swift's handling of inout in type signatures for some cases.

Until the bug is addressed, you can work around it by using an UnsafeMutablePointer .

func increment(a: UnsafeMutablePointer<Int>) {
    a.memory += 1
}
let functionArray = [increment]

var thing = 2
functionArray2[0](&thing)
println(thing) // 3