在哪里实现 Swift 协议? [英] Where to implement Swift protocols?

问题描述

在 Swift 中实现协议一致性时，我有两个选择，最终结果相同:

I have two options when implementing protocol conformance in Swift, with the same end result:

• 在类内实现协议 - 即在类定义的顶部声明一致性，并将实现放在类体内，或者
• 在扩展中实现协议 - 也就是说，完全在类之外编写协议一致性.

• Implement the protocol within the class - that is, state the conformance at the top of class definition, and put implementation inside the class body, or
• Implement the protocol in an extension - that is, code up protocol conformance entirely outside the class.

这是一个例子:

public class MyClass : CustomDebugStringConvertible {
    ... // Something
    public var debugDescription : String {
        return "MyClass"
    }
}

对比

class MyClass {
    ... // Something
}
extension MyClass : CustomDebugStringConvertible {
    public var debugDescription: String {
        return "MyClass"
    }
}

Swift 书籍中的代码示例倾向于关注第一种方法；Apple 的 Swift 核心源代码表明他们只使用第二种方法(请参阅 Bool 和 Optional 为例).

Code samples in Swift books tend to concentrate on the first approach; Apple's source code of Swift core reveals that they use only the second approach (see Bool and Optional for an example).

是否有一种合理的方式可以根据情况在两种方法之间做出决定，还是仅仅是编码偏好的问题?

Is there a sound way to decide between the two approaches depending on the situation, or is it simply a matter of coding preference?

推荐答案

我主要将其视为编码偏好.在我的团队中，我们已经开始采用第二种方法.起初我认为这是扩展的奇怪用法，但我开始喜欢它.它将协议的实现方法很好地结合在一起，并给人的印象是类本身更小(实际上只是光学).如果类有一个 tableview 并且您使用扩展来实现数据源和委托，我会看到一些复杂情况或混淆的机会.如果有人随后对该类进行子类化，他们可能不知道该扩展并会看到意外行为.

I see it mostly as coding preference. In my team here we have started to adopt the second approach. At first I thought it was an odd use of extension but I have come to like it. It keeps the implemented methods of a protocol nicely together and gives the impression that the class itself is smaller (just optics really). I could see some complications or opportunities for confusion if, say, the class has a tableview and you use extensions to implement the datasource and delegate. If someone then subclasses that class, they might not be aware of the extension and see unexpected behavior.

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