swift - Swift 协议(protocol)元类型的运行时比较

Question

我正在尝试将 Swift 协议(protocol)与实现动态匹配，但我在尝试在运行时执行协议(protocol)比较时遇到了阻碍 - 似乎协议(protocol)在运行时可能并不存在？

我尝试过的一些例子:

var protocols[Any]

func findProtocol(aProtocol: Any) -> Bool {
    // Nope, protocols don't implement equatable
    aProtocol == protocols[0]

    // Doesn't work, unsafeAddressOf() only applies to AnyObjects
    let pointer: UnsafePointer = unsafeAddressOf(aProtocol) 

}

我想我可能已经触及了试图打败类型系统的界限……有什么想法吗？

Answer 1

如果您知道比较类型本身，您应该使用更合适的类型 (Any.Type):

var protocolArray: [Any.Type] = [...]

func findProtocol(aProtocol: Any.Type) -> Bool {
    // you can do that because Any.Type has an == operator
    return protocolArray.contains{ $0 == aProtocol }
}

对于 Any 类型，你必须转换它:

var protocolArray: [Any] = [...]

func findProtocol(aProtocol: Any) -> Bool {
    return protocolArray.contains{
        if let p1 = $0 as? Any.Type, p2 = aProtocol as? Any.Type {
            return p1 == p2
        }
        return false
    }
}