Swift generic array with type constraint

Question

I'm trying to write a swift method that returns a generic array. I've left out some of the details, but kept the important bit that isn't working for clarity...

protocol AProtocol {
    func doSomething()
}

func decode<T: AProtocol>(jsonArray: Array<AnyObject>?) -> [T: AProtocol] {
    //...
    var resultArray = [T: AProtocol]()
    resultArray.append
    //...
}

When I specify that the array contains type T: AProtocol, then the append method no longer appears

[T: AProtocol] does not have a member named append

Antonio · Accepted Answer · 2014-11-24 11:46:33Z

3

In this line of code:

var resultArray = [T: AProtocol]()

you are creating a dictionary having key of T type and value of AProtocol type.

To create an array of AProtocol, just use:

var resultArray = [AProtocol]()

otherwise if you want an array of T:

var resultArray = [T]()

Note that the constraint of T implementing the AProtocol protocol is set in the function declaration, so you don't have to repeat it again when using T in the function body.

answered Nov 24, 2014 at 11:46

Antonio

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Kirsteins · Accepted Answer · 2014-11-24 11:46:29Z

1

This [T: AProtocol]() is not array, but dictionary.

answered Nov 24, 2014 at 11:46

Kirsteins

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