Swift: execution of a function as parameter

Question

I'm trying to accomplish the following task (using the playground): store in an array a list of functions and later execute them.

What I'm doing is:

func f1(){
    println("f1")
}

var a : [(a: Int, b: (Void) -> Void)] = []

a.append(a: 2, b: f1)

for(var i = a.count-1; i >= 0; i--){
    a[i].b()
}

The error I'm getting is the following: "Execution was interrupted, reason: EXC_BAD_ACCESS (code=EXC_I386_GPFLT)" just on the call:

a[i].b()

while if I type:

a[i].b

Playground suggest me: "(Function)"

Any idea on how I could do this? How could I execute the function? Thanks

Even though Swift seems to prefer the Unnamed tuples the problem seems to be solved with the new Swift version 1.2 (In my tests that worked only with unnamed tuples)

You've made that example very hard to understand by using a twice. Can you not use proper words instead of a, a, and b. — Fogmeister
– Fogmeister, Commented Dec 4, 2014 at 18:10
Looks like a bug to me. Same exception here when running in Debug mode, and Xcode 6.1.1 crashes when compiling that in Release mode. — Martin R
– Martin R, Commented Dec 4, 2014 at 18:13

Antonio · Accepted Answer · 2014-12-04 19:45:25Z

1

That definitely smells like a bug. Decomposing the expression it runs without problems in storyboard:

for(var i = a.count-1; i >= 0; i--){
    let element = a[i]
    let method = element.b
    method()
}

It's probably something related to closures when used in tuples.

I verified that removing the integer value from the tuple, it works:

var a : [((Void) -> Void)] = []

a.append(f1)

for(var i = a.count-1; i >= 0; i--){
    a[i].0()
}

Inverting the order (closure first, integer last) has no effect instead.

answered Dec 4, 2014 at 19:45

Antonio

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