问题描述

如何在 Swift 中使用 Comparable 协议?在声明中它说我必须实现三个操作 <、<= 和 >=.我把所有这些都放在课堂上，但它不起作用.我还需要拥有这三个吗?因为应该可以从一个推导出所有这些.

How do I use the Comparable protocol in Swift? In the declaration it says I'd have to implement the three operations <, <= and >=. I put all those in the class but it doesn't work. Also do I need to have all three of them? Because it should be possible to deduce all of them from a single one.

推荐答案

Comparable 协议扩展了 Equatable 协议 -> 实现它们两个

The Comparable protocol extends the Equatable protocol -> implement both of them

在 Apple's Reference 中是来自 Apple (在 Comparable 协议参考中)你可以看到你应该怎么做:不要把操作实现放在类中，而是放在外部/全局范围内.此外，您只需实现 Comparable 协议中的 < 运算符和 Equatable 协议中的 == 运算符.

In Apple's Reference is an example from Apple (within the Comparable protocol reference) you can see how you should do it: Don't put the operation implementations within the class, but rather on the outside/global scope. Also you only have to implement the < operator from Comparable protocol and == from Equatable protocol.

正确示例:

class Person : Comparable {
    let name : String

    init(name : String) {
        self.name = name
    }
}

func < (lhs: Person, rhs: Person) -> Bool {
    return lhs.name < rhs.name
}

func == (lhs: Person, rhs: Person) -> Bool {
    return lhs.name == rhs.name
}

let paul = Person(name: "Paul")
let otherPaul = Person(name: "Paul")
let ben = Person(name: "Ben")

paul > otherPaul  // false
paul <= ben       // false
paul == otherPaul // true

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