1.什么是空白标识符
空白标识符是未使用的值的占位符。它由下划线（_）表示。由于空白标识符没有名称，因此它们也被称为匿名占位符。
在 Go 语言中， 不允许声明未使用的变量或导入语句。也就是说，我们无法声明变量并将其留下未使用。同样，如果您导入一个包，那么也必须使用它。
这个时候就需要一个空白标识符。
2.未使用的赋值变量
如果 Go 中的函数返回多个值，则必须定义相等数量的变量来保存这些值。但是，如果您只需要其中一些值而不需要其他值，若某次赋值需要匹配多个左值，但其中某个变量不会被程序使用， 那么用空白标识符来代替。该变量可避免创建无用的变量，并能清楚地表明该值将被丢弃。
如下所示：
result, error = Dosomething()
if error {
// handle error
} 在上面的代码中，result 与程序无关，而且后续代码也没有使用它。如果编译的话，Go 编译器会报错。
result declared but not used 在这种情况下，您可以将结果替换为下划线或空白标识符，
如下所示：
_, error = Dosomething()
if error {
// handle error
} 即使您声明了一个变量，您也可以稍后使用空白标识符来忽略它，如下面的代码所示：
product, error = Dosomething()
if error {
// handle error
}
// ignore unused variable
_ = product 在 for…range 中使用空白标志符
func Sum(numbers []int) int {
sum := 0
for _, number := range numbers {
sum += number
}
return sum
} 3.未知的结构体
可以利用 _ 分配任何东西:
var _ I = T{} 无法访问此变量，以便将从生成的程序中优化。但是，如果 T 类型未分配给接口 I ，则可能会导致编译错误。因此，在这种情况下，它被用作关于类型的静态断言。
4.未使用的包
在 Go 中，如果你导入一个包，那么你必须使用它，否则会出现编译器错误。
imported and not used “” 空白标识符可用于解决此编译器错误。
有两种方法可以使用空白标识符来解决未使用的包错误，如下所示:
第一种：声明一个全局空白标识符（在 main() 函数之前），该标识符从未使用的包中访问符号，例如下面代码中的 Open：
import "os"
var _ = os.Open
func main() {
} 第二种：在未使用的包前加上一个空白标识符，
如下所示：
import _ "os"
func main(){
} 空白标识符通过避免在整个代码中使用未使用的变量声明，使代码更具可读性。
5.总结
Golang 中任何声明但未使用的包和变量都会引发错误。这一规则使得我们的代码保持干净和轻量。
有时如果需要在未来使用并提前导入一些软件包，就可以使用空白标识符。
有时候函数会返回多个参数，但是我们只需要使用其中一个变量的时候，就可以通过空白标志符来进行接收。
到此这篇关于Go 中的空白标识符下划线的文章就介绍到这了。
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