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在两个协议对象上使用equals

equatable protocols operator-overloading swift

0

Yogurt · 技术社区 · 6 年前

理想情况下,我会让服务器实现可平等协议,但我遇到了问题。这是我的密码

protocol Server {
    var ipAddress: String { get }
    // simplified for this question
}

func ==<T:Server>(lhs: T, rhs: T) -> Bool {
    return lhs.ipAddress == rhs.ipAddress
}

func !=<T:Server>(lhs: T, rhs: T) -> Bool {
    return lhs.ipAddress != rhs.ipAddress
}

func ==<T:Server, U:Server>(lhs: T, rhs: U) -> Bool {
    return lhs.ipAddress == rhs.ipAddress
}

func !=<T:Server, U:Server>(lhs: T, rhs: U) -> Bool {
    return lhs.ipAddress != rhs.ipAddress
}

func doSomething(server0: Server, server1: Server) {
    // I want to compare to Server objects

    // !!! Compile Error !!!
    // Binary operator '==' cannot be applied to two 'Server' operands
    guard server0 == server1 else {
        print("SAME BAD")
        return
    }

    print("DO stuff")
}

我是不是疯了?:P页

1 回复 | 直到 6 年前

1

0

Cristik 6 年前

如果将函数设为泛型,则问题将消失:

func doSomething<T1: Server, T2: Server>(server0: T1, server1: T2) {

这是必需的,因为在Swift中 protocols don't conform to base protocols, not even to themselves

以下代码也会发生同样的错误:

struct A: Server {
    let ipAddress: String = ""
}

let server1: Server = A()
let server2: Server = A()
print(server1 == server2) // Binary operator '==' cannot be applied to two 'Server' operands

错误的原因相同: Server 不符合 (听起来很奇怪)。这意味着声明接收协议的函数不能通过向其传递协议来调用,您需要告诉编译器您传递的协议的具体实现。