How to use an array of functions in Swift

Question

I have read all the posts I can find here about arrays of functions - great you can do it. I figured. But none of the posts show practically how to use them (at least not what I'm trying to do). Here's what I want - they can all take the same args, but that's not a requirement.

This article is close, and will allow me to loop through to execute each function (which meets the first goal).
https://stackoverflow.com/a/24447484/11114752

But... what if I want to execute a single function by reference? In other words, how to call just the referenced Arity2 function - for example:

// None of these work (with or without the parameter labels)
funcs.Arity2(n: 2, S: "Fred)    // value of type [MyFuncs] has no member .Arity2
funcs[Arity2](n: 2, S: "Fred")  // no exact matches to call in subscript
funcs[.Arity2](n: 2, S: "Fred") // Cannot call value of non-function type...

let fn = funcs.first(where: { a whole ton of permutations here to try to match Arity2 }) -- a whole lotta frustrating nope...

Help, please! Nothing I've tried works. The pre-compiler just goes in circles making suggestions that don't pan out and it will not compile.

EDIT: The reason for the array in the first place is that I'm going to have a quite a few functions, and I don't know what they all are in advance. Essentially, I want a plugin type of architecture. Where I can add to the list of functions (ideally within an extension of the class, but that's another problem..) and not change the processing loop that executes each function in order.

Does this answer your question? How to access a Swift enum associated value outside of a switch statement — pawello2222
– pawello2222, Commented Sep 3, 2020 at 22:36
There's no need for the complexity of the answer you're following (unless you're doing something much more complicated than you're describing). Check the following answer to the same question (a lot of the answers on that page are dealing with pre-1.0 Swift): stackoverflow.com/a/26416417/97337 Write up an example of a couple of functions you're trying to call. How would you do this without an array? Just hard code them and show what you want to call, and we'll show how to turn that into an array. — Rob Napier
– Rob Napier, Commented Sep 3, 2020 at 22:39
I tried the pawello2222's answer - it does not work right with functions, which is my frustration. — Michael Stone
– Michael Stone, Commented Sep 3, 2020 at 22:56
@Rob - that's my alternative and what I'm working with now. First goal - execute all functions (in array order - first function first, second, ...). Second goal - access individually by name. So, looks like I'll need two arrays unless the named one also maintains the order they're declared (will need some testing). — Michael Stone
– Michael Stone, Commented Sep 3, 2020 at 22:59

Asperi · Accepted Answer · 2020-09-04 07:20:01Z

1

I assume you need something like

    _ = funcs.first {
        if case let MyFuncs.Arity2(f) = $0 {
            f(2, "Fred")
            return true
        }
        return false
    }

answered Sep 4, 2020 at 7:20

Asperi

262k28 gold badges594 silver badges888 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Michael Stone Over a year ago

YES!! That's the magical incantation I was looking for - combining if, case and .first. Wow - gotta love Swift :). Given the complexity and the fact that I have to deal with a conditional, I'm rethinking my approach - but this answers the question - thank you.

Michael Stone Over a year ago

Rechecked: This does seem to work even if I only know the name

pawello2222 · Accepted Answer · 2020-09-04 15:25:59Z

0

It can be achieved in a much simpler way if you know the position of the function in the array.

Assuming you have:

func someFunc(n: Int, s: String) { 
    print("call \(n) \(s)")
}

var funcs = [MyFuncs.Arity2(someFunc)]

you can do:

if case .Arity2(let f) = funcs.first {
    f(2, "Fred")
}

By replacing funcs.first with funcs[i] you can access the i-th index (first make sure it does exist).

edited Sep 4, 2020 at 15:25

answered Sep 4, 2020 at 13:44

pawello2222

55.6k23 gold badges184 silver badges240 bronze badges

6 Comments

Michael Stone Over a year ago

I like this. It compiles without complaint. However, I confirmed, in init(), I have: funcs.append(MyFuncs.Arity2(someFunc)) Also confirmed funcs contains Arity2 in debugger. But the if statement never fires (using either .first or [0])

pawello2222 Over a year ago

@MichaelStone I assumed you know the position of your function in the array.

Michael Stone Over a year ago

code var lFn = Array<MyFuncs>(). ... init(){ lFn.append(MyFuncs.Arity2(someFunc)) }. ... suggested if block above never executes the function. But this would be great if it did! I know the name (Arity2) and the position (0), but neither funcs.first, nor funcs[0] seems to satisfy the condition. Although I may not know the position in my actual usage. I was wrong, position is 1, and that does work. So, I still need .first(where; ...) if I only know the name.

pawello2222 Over a year ago

@MichaelStone Yes, it only works if you know the position. Otherwise you need to search for the first matching signature as Asperi suggested.

Michael Stone Over a year ago

Yeah, again - unless I'm missing something, it only seems to work if I specify the correct position (eg: if Arity2 is really the first element, or if I specify the correct position in brackets). I have as in the example Arity0 as the first element now and Arity2 in the second to ensure I am testing the correct scenario.

|

Collectives™ on Stack Overflow

How to use an array of functions in Swift

2 Answers 2

2 Comments

6 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

6 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related