Swift 什么时候需要参数标签? [英] When are argument labels required in Swift?

问题描述

在回答这个问题时，关于调用<代码>初始化.这在 Swift 中很正常.

In answering this question it came about that argument labels were required for a call to init. This is normal in Swift.

class Foo {
    init(one: Int, two: String) { }
}

let foo = Foo(42, "Hello world") // Missing argument labels 'one:two:' in call

然而，陌生人的力量正在发挥作用:

However, stranger forces are at play:

extension Foo {
    func run(one: String, two: [Int]) { }
}

foo.run(one: "Goodbye", two: []) // Extraneous argument label 'one:' in call

要在此处使用参数标签，必须明确声明.

To use an argument label here it would have to be declared explicitly.

我还没有在文档中看到对所有这些进行非常彻底的解释.哪些类/实例/全局函数需要参数标签?Obj-C 方法是否总是使用参数标签导出和导入?

I haven't seen something very thorough explaining all of this in the documentation. For which varieties of class/instance/global functions are argument labels required? Are Obj-C methods always exported and imported with argument labels?

推荐答案

从 Swift 3.0 开始，这又发生了变化:所有方法、函数和初始值设定项都需要 所有 参数的参数标签，除非您有使用外部名称 _ 明确选择退出.这意味着诸如 addChildViewController(_:) 之类的方法现在是这样编写的:

As of Swift 3.0 this has changed again: all methods, functions, and initializers require argument labels for all parameters, unless you have explicitly opted out using the external name _. This means methods such as addChildViewController(_:) are now written like this:

func addChildViewController(_ childController: UIViewController)

这是提议和批准的一部分Swift Evolution 流程，并在 SR-961.

This was proposed and approved as part of the Swift Evolution process, and was implemented in SR-961.

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