swift 2 Func 默认类型参数

Question

给定以下代码：

protocol NetworkWire {
//some requirements
}

protocol EntityRESTRequest {
//some requirements
}

protocol OctupPromisable {
//some requirements
}

final class HTTPNetworkWire: NetworkWire, EntityRESTRequest, OctupPromisable {
//satisfies all requirements
}

我现在像这样创建一个函数，

extension NSManagedObject {

func post<T where T:NetworkWire, T:EntityRESTRequest, T:OctupPromisable>(navigationalProperties: String, networkWireType: T.Type = HTTPNetworkWire) -> OctupPromisable {
    //some logic with valid return
    }

}

编译器在 post 函数上给我一个错误，说

HTTPNetworkWire.Type 的默认参数无法转换为类型 T.type

知道这是为什么吗？虽然 HTTPNetworkWire 符合 NetworkWire,EntityRESTRequest 以及 OctupPromisable!

任何想法将不胜感激。运行 Xcode 7.1.1

Answer 1

您应该使用 Protocol Composition 而不使用泛型：

extension NSManagedObject {

    func post(navigationalProperties: String, networkWireType: protocol<NetworkWire, EntityRESTRequest, OctupPromisable>.Type = HTTPNetworkWire.self) -> OctupPromisable {
        //some logic with valid return
    }

}

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