Go中下划线（空白标识符）的含义

问题描述

   >是一个特殊的标识符，你可以指定任何东西但永远不会读取。在第一个示例中，您给出了： 
 
 
  var _ I = T {} 
  
没有办法访问这个变量，所以它会被优化出最终的程序。但是，如果类型 T 不能分配给接口 I ，则可能会导致编译错误。所以在这种情况下，它被用作关于类型的静态断言。
 
 
 
第二种情况更常见。虽然扔掉函数调用的结果似乎很奇怪，但在具有多个返回值的函数中它可能更有意义。考虑一个函数 foo ，它返回两个值，但您只对第一个值感兴趣？您可以使用 _ 忽略第二个： 
 
 
  a，_ = foo（）
  
通过创建另一个变量来保存不需要的返回值，您可以获得相同的效果，但此功能意味着您无需担心为其选择唯一的名称。
 
As I was reading the Go docs I found this:
type T struct{}
var _ I = T{} // Verify that T implements I.
I don't understand what the _ is used for and I've seen it in other assignments but cannot understand what it means. Digging deeper I found that it's called "blank identifier" but I don't understand the use case they put:
_ = x // evaluate x but ignore it
Go idioms still feel a little alien to me so I'm trying to understand why I would want to do  something like this.
 解决方案 
_ is a special identifier you can assign anything to but never read from.  In the first example you gave:
var _ I = T{}
There is no way to access this variable so it will be optimised out of the resulting program.  However, it could cause a compile error if the type T is not assignable to the interface I.  So in this case it is being used as a static assertion about a type.
The second case is more common.  While it might seem strange to throw away the result of a function call, it can make more sense in functions with multiple returns.  Consider a function foo that returns two values but you're only interested in the first?  You can use _ to ignore the second:
a, _ = foo()
You could get the same effect by creating another variable to hold the unwanted return value, but this feature means you don't need to worry about picking a unique name for it.
                        
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