使用符合 swift 2.0 协议的元素扩展数组

Question

我正在尝试为 Array 结构创建一个扩展，以便在包含的对象符合特定协议时添加方法，但是当我尝试访问来自 class.

的扩展

这是我的游乐场代码

protocol SomeInt {
    var theInt: Int {get set}
}

extension Array where Element: SomeInt {
    func indexOf(object:SomeInt) -> Index? {
        return indexOf({ (obj) -> Bool in
            return obj.theInt == object.theInt
        })
    }
}

class PRR: SomeInt {
    var theInt: Int = 0
    init(withInt value: Int){
        theInt = value
    }
}

class container {
    var items: [SomeInt]!
}

let obj1 = PRR(withInt: 1)
let obj2 = PRR(withInt: 2)

let arr = [obj1, obj2]
arr.indexOf(obj1) //this succeds

let cont = container()
cont.items = [obj1, obj2]
cont.items.indexOf(obj1) //this doesn't

知道哪里出了问题吗？？

Answer 1

好的，看起来这是一个众所周知的行为...因为有人是一个错误。

Actually, no, this is just a known limitation of the compiler. Unfortunately, today, the protocol type (or "existential" as we compiler weenies call it) doesn't conform to the protocol:

protocol P {}  
func g<T: P>(_: T) {}  
struct X : P {}  
struct Y<T: P> {}  
Y<P>() // error: type 'P' does not conform to protocol 'P'

来源：https://forums.developer.apple.com/message/15955#15955

使用符合 swift 2.0 协议的元素扩展数组

Extension of array with Elements conforming a protocol in swift 2.0

generics

swift-extensions

swift2