... interface {}(点点接口)的含义 [英] Meaning of ...interface{} (dot dot dot interface)

问题描述

下面是我有疑问的Go代码. 具体来说，此功能中的a是什么?

Below is a piece of Go code I have question about. Specifically, what is a in this function?

func DPrintf(format string, a ...interface{}) (n int, err error) {
  if Debug > 0 {
    n, err = fmt.Printf(format, a...)
  }
  return
}

谁能告诉我这三个点是什么? ...interface{}是做什么的?

Could anyone tell me what the three dots are here? And what does ...interface{} do?

推荐答案

以三个点(...)为前缀的参数类型称为 variadic参数.这意味着您可以将任何数字或参数传递给该参数(就像使用fmt.Printf()一样).该函数将接收参数的参数列表，作为参数声明的类型的切片(在您的情况下为[]interface{}). 转到规范指出:

A parameter type prefixed with three dots (...) is called a variadic parameter. That means you can pass any number or arguments into that parameter (just like with fmt.Printf()). The function will receive the list of arguments for the parameter as a slice of the type declared for the parameter ([]interface{} in your case). The Go Specification states:

函数签名中的最后一个参数可以具有以...为前缀的类型.具有此类参数的函数称为可变参数(variadic)，并且可以使用该参数的零个或多个参数来调用.

The final parameter in a function signature may have a type prefixed with .... A function with such a parameter is called variadic and may be invoked with zero or more arguments for that parameter.

一个参数:

a ...interface{}

是，对于等同于以下功能的功能:

Is, for the function equivalent to:

a []interface{}

区别在于如何将参数传递给此类函数.可以通过分别给切片的每个元素或作为单个切片来完成此操作，在这种情况下，您必须在切片值后缀三个点.以下示例将导致相同的调用:

The difference is how you pass the arguments to such a function. It is done either by giving each element of the slice separately, or as a single slice, in which case you will have to suffix the slice-value with the three dots. The following examples will result in the same call:

fmt.Println("First", "Second", "Third")

将执行以下操作:

s := []interface{}{"First", "Second", "Third"}
fmt.Println(s...)

在转到规范中也对此进行了很好的解释:

This is explained quite well in the Go Specification as well:

给出函数并调用

Given the function and calls

   func Greeting(prefix string, who ...string)
   Greeting("nobody")
   Greeting("hello:", "Joe", "Anna", "Eileen")

在Greeting之内的

中，who在第一个调用中将具有值nil，在第二个调用中将具有[]string{"Joe", "Anna", "Eileen"}.

within Greeting, who will have the value nil in the first call, and []string{"Joe", "Anna", "Eileen"} in the second.

如果最终参数可分配给切片类型[]T，则在参数后跟...的情况下，可以将其不变地作为...T参数的值传递.在这种情况下，不会创建新的切片.

If the final argument is assignable to a slice type []T, it may be passed unchanged as the value for a ...T parameter if the argument is followed by .... In this case no new slice is created.

给出切片s并调用

   s := []string{"James", "Jasmine"}
   Greeting("goodbye:", s...)

在Greeting之内，who将具有与s相同的值，并且具有相同的基础数组.

within Greeting, who will have the same value as s with the same underlying array.

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