How to instantiate multiple instances of the same generic protocol with different types in swift?

Question

I have a generic protocol P, and I want other class B to have different instances of this protocol with different types. I want to simulate the following behavior:

protocol P<T> {
    func getAll() -> [T]
}

class B {
    var foo1: P<Int>

    var foo2: P<String>
}

How can I accomplish this in swift?

Answer 1

You can't do that with protocols in Swift. You can do something similar:

protocol P {
    typealias T
    func getAll() -> [T]
}

class C : P {
    typealias T = Int
    func getAll() -> [T] {
        return []
    }
}

class D : P {
    typealias T = String
    func getAll() -> [T] {
        return []
    }
}

struct B {
    var foo1: C
    var foo2: D
}

Answer 2

Probably this is what you are looking for:

protocol P {
    typealias T
    func getAll() -> [T]
}

extension Int: P {
    func getAll() -> [Int] {
        return [1, 2, 3]
    }
}

extension String: P {
    func getAll() -> [String] {
        return ["foo", "bar", "zoo"]
    }
}

class B {
    var foo1: Int = 0

    var foo2: String = ""
}

let x = B()
x.foo1.getAll()
x.foo2.getAll()

Answer 3

Is this what you are trying to accomplish?

protocol P {
    typealias T
    func getAll() -> [T]
}

class IntGetter: P {
    typealias T = Int
    func getAll() -> [T] {
        return [1,2,3]
    }
}

class StringGetter: P {
    typealias T = String
    func getAll() -> [T] {
        return ["a", "b", "c"]
    }
}

let i = IntGetter()
i.getAll() // [1,2,3]

let s = StringGetter()
s.getAll() // ["a","b","c"]