CODEWITHSUNDEEP
arraysswiftgenerics
Alex
Alex

Reputation: 5119

Array of generic type as argument to function

This is a very simple problem to explain, but it's driving me nuts!

I have a generic Event class:

class Event<T> {
    // Etc...
}

On that class I want to add a class function that takes an array of Events and returns another generic type (EventListener):

public class func listenAny<V>(listener: AnyObject, events: [Event<V>]) -> EventListener<V> {
    // Etc...
}

For some reason, this code doesn't compile!

let e1 = Event<Int>()
let e2 = Event<Int>()

class Listener {}
let l = Listener()

Event.listenAny(l, events: [e1, e2])

The compiler throws an error on the last line:

error

Here's a piece of code that you can paste on a Playground (I tested this on a Playground on Xcode 6.1.1) and experience the frustration for yourself:

public class Event<T> {
    private var eventListeners = [EventListener<T>]()

    public class func listenAny<V>(listener: AnyObject, events: [Event<V>]) -> EventListener<V> {
        let eventListener = EventListener<V>(listener: listener)
        for event in events { event.addListener(eventListener) }
        return eventListener
    }

    private func addListener(listener: EventListener<T>) -> EventListener<T> {
        eventListeners.append(listener)
        return listener
    }
}

public class EventListener<T> {
    weak public var listener: AnyObject?
    private init(listener: AnyObject) {
        self.listener = listener
    }
}



let e1 = Event<Int>()
let e2 = Event<Int>()

class Listener {}
let l = Listener()

let v = [e1, e2]
Event.listenAny(l, events: v)

Why is this not working?

PS: I intend for the array of events to be a variadic parameter. I hope that if I get this to work with an array, I can do the same with a variadic parameter.

PSS: It seems that if I make the listenAny a global function, it works. It might be a problem with the type system (T from Event in conjunction with V from the function...)

Upvotes: 0

Views: 695

Answers (1)

Reynaldo Aguilar
Reynaldo Aguilar

Reputation: 1936

You need to supply the generic type of the class Event. The following code compiles correctly:

Event<Int>.listenAny(l, events: v)

Note: I use Int as the generic type, but you can use any type.

Upvotes: 1

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