具有类型约束的Swift通用数组

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

Answer 1

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.

Answer 2

这[T: AProtocol]()不是数组，而是字典。