什么是 _: 在 Swift 中告诉我的? [英] What is _: in Swift telling me?

问题描述

函数定义中的下划线是什么意思?

What does the lone underscore mean in function definitions?

例如map(_:)

我知道在定义函数时我可以:

I understand that when defining functions I can do:

func myFunc(_ string: String) { ... }

我会不会将其称为 myFunc(_:) 而不是 myFunc(_string:)，即故意隐藏参数名称?

Would I then refer to that as myFunc(_:) instead of myFunc(_string:), i.e. purposefully hiding the parameter name?

推荐答案

_ 用于定义参数未命名

如果你有多个 _ 它表明你不需要在函数调用中命名参数

If you have multiple _ it states that you do not need to name the parameters in your function call

func myFunc(name:String, _ age:String){
}

myFunc("Milo", "I'm a really old wizard")

如果你不使用下划线，你会使用

If you do not use the underscore you would use

myFunc("Milo", age: "I'm a really old wizard")

_ 不是函数调用所必需的.它只是用来表示不需要名字的东西.

The _ is not necessary for function calls. It is just used to indicate that something does not need to have a name.

关于如何引用您的函数，您不必为函数调用传递任何名称.
但是由于你也没有定义参数类型，这在我看来就像一个无效的例子(它至少在 Swift 2.0 的 Xcode 7 中不起作用)

In regards to how you would refer to your function, You would not have to pass any name for the function call.
But since you also don’t define a parameter type this seems to me like an invalid example (it at least doesn’t work in Xcode 7 with Swift 2.0)

从 Swift 3.0 开始

Since Swift 3.0

myFunc(name: "Milo", age: "I'm a really old wizard")

应该使用

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