Swift 协议元类型的运行时比较

Question

我正在尝试将 Swift 协议动态匹配到一个实现，但我在尝试在运行时执行协议比较时遇到了阻碍 - 似乎协议可能并不真正存在于运行时间？

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

我可能有点误解你想要做什么，但你应该能够为此使用反射。像这样的怎么样？

protocol One {}
protocol Two {}
protocol Three {}

var protocols: [Any] = [One.self, Two.self]

func findProtocol(aProtocol: Any) -> Bool {

    let findMirror = Mirror(reflecting: aProtocol)

    for checkProtocol in protocols {
        let mirror = Mirror(reflecting: checkProtocol)

        if findMirror.subjectType == mirror.subjectType {
            return true
        }
    }
    return false
}

findProtocol(One) // Returns true
findProtocol(Two) // Returns true
findProtocol(Three) // Returns false

Answer 2

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{ [=10=] == aProtocol }
}

对于 Any 类型，您必须强制转换它：

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

func findProtocol(aProtocol: Any) -> Bool {
    return protocolArray.contains{
        if let p1 = [=11=] as? Any.Type, p2 = aProtocol as? Any.Type {
            return p1 == p2
        }
        return false
    }
}

Swift 协议元类型的运行时比较

Runtime comparison of Swift Protocol MetaTypes

swift

swift2