swift generic type constraints

type-constraints.swift

protocol Foobery {
    func asFoo() -> String
}

extension String: Foobery {
    func asFoo() -> String {
        return "foo"
    }
}

extension Int: Foobery {
    func asFoo() -> String {
        return "bar"
    }
}

struct Stack<T: Foobery> {
    var collection = T[]()

    mutating func push(item: T) {
        collection.append(item)
    }

    mutating func pop() -> T {
        return collection.removeLast()
    }
}

var stack = Stack<String>()
stack.push("first")
stack.push("second")
let second = stack.pop()
second.asFoo()
stack.pop()
stack


struct Ztack {
    var collection = Array<Foobery>()

    mutating func push(item: Foobery) {
        collection.append(item)
    }

    mutating func pop() -> Foobery {
        return collection.removeLast()
    }
}

var ztack = Ztack()
ztack.push("first")
ztack.push("second")
ztack.push(123)
let zhird = ztack.pop()
zhird.asFoo()
let zecond = ztack.pop()
zecond.asFoo()
ztack.pop()
ztack