How can I create an array of functions?

Question

I'm trying to build out a basic implementation of Promises in Swift, and I need to be able to add functions to an array, but I'm not sure how to get that to work.

class Promise {
    var pending = []

    func resolve() -> Void {
    }

    func then(success: (Void -> Void)) -> Promise {
        // how do I add success to pending array?
        return self
    }
}

let p = Promise()
p.then({println("finished")})

What I'm finding is that the Swift Playground won't suggest append when I try to do something like this:

self.pending.append(success)

Which makes sense - Swift can't infer the type of self.pending - but that's where my problem lies. I'm not sure how to predefine an array of (Void -> Void) functions.

Is it possible to create an array of functions in Swift? I would assume so, with functions being first-class citizens.

I haven't tried this, but does the obvious var pending: (Void->Void)[] = [] not work? — Chuck
– Chuck, Commented Jun 6, 2014 at 18:44
The Swift playground doesn't seem to like var pending = (Void -> Void)[] = [] — Rob
– Rob, Commented Jun 6, 2014 at 18:46

Gabriele Petronella · Accepted Answer · 2014-10-06 16:11:24Z

26

It's definitely possible, just initialize the array as:

var pending = Array<(Void -> Void)>()

or even a fancier

var pending = Array<()->()>()

or

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

or

var pending: [(()->())] = []

or

var penguins: [<(") <(")] = [] // kidding

edited Oct 6, 2014 at 16:11

answered Jun 6, 2014 at 18:43

Gabriele Petronella

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8 Comments

Sulthan Over a year ago

or (Void -> Void)[]

Rob Over a year ago

(Void -> Void)[] doesn't work for me, but `Array<(Void -> Void)> works perfectly

Gabriele Petronella Over a year ago

If you want to get fancier you can use Array<()->()>()

Sulthan Over a year ago

@AlexWayne I meant var array: (() -> ())[] = [] or var array: (Void -> Void)[] = []

Alex Wayne Over a year ago

Neat! Here's a fuller complete working example: gist.github.com/Squeegy/5d5c73a373b0c4839280

|

sanz · Accepted Answer · 2014-06-06 18:46:42Z

4

This should work:

var pending: (() -> ())[]

answered Jun 6, 2014 at 18:46

sanz

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