英文:
How to implement _() method?
问题
我发现一个接口中有一个名为_的方法。我尝试实现它，但是它不起作用：
package main
func main() {}
func ft(t T) { fi(t) }
func fi(I) {}
type I interface {
_() int
}
type T struct {}
func (T) _() int { return 0 }
func (T) _(int) int { return 0 }
运行代码后报错：
./a.go:4: cannot use t (type T) as type I in function argument:
T does not implement I (missing _ method)
我还尝试添加重载的方法_(int)，但也不起作用：
package main
func main() {}
type I interface {
_() int
_(int) int
}
type T struct {}
func (T) _() int { return 0 }
func (T) _(int) int { return 0 }
运行代码后报错：
# command-line-arguments
./a.go:12: internal compiler error: sigcmp vs sortinter _ _
为什么会这样？_方法的目的是什么？我认为它可能是一种防止人们实现接口的方式（类似于Java中的私有接口）？
英文:
I found an interface with a method called _ in it. I tried implementing it, but it's not working:
package main
func main() {}
func ft(t T) { fi(t) }
func fi(I) {}
type I interface {
_() int
}
type T struct {}
func (T) _() int { return 0 }
func (T) _(int) int { return 0 }
<!
$ go run a.go
./a.go:4: cannot use t (type T) as type I in function argument:
T does not implement I (missing _ method)
I also tried adding the overloaded method _(int) but that's not working either:
package main
func main() {}
type I interface {
_() int
_(int) int
}
type T struct {}
func (T) _() int { return 0 }
func (T) _(int) int { return 0 }
<!
$ go run a.go
# command-line-arguments
./a.go:12: internal compiler error: sigcmp vs sortinter _ _
Why? What is the purpose of this _ method? I think it might be a way to prevent people from implementing the interface (like private interfaces in Java)?
答案1
得分: 5
_ 是“空白标识符”（https://golang.org/ref/spec#Blank_identifier），具有特殊规则。具体来说：
空白标识符可以像声明中的任何其他标识符一样使用，但它不引入绑定，因此不会被声明。
还要注意接口部分（https://golang.org/ref/spec#Interface_types）中的说明：
每个方法必须具有唯一的非空白名称
所以该接口甚至不是有效的Go代码；编译器似乎接受它是一个错误。声明该接口的包不应该这样做。
英文:
_ is the "blank identifier" (https://golang.org/ref/spec#Blank_identifier) and has special rules. Specifically:
> The blank identifier may be used like any other identifier in a declaration, but it does not introduce a binding and thus is not declared.
Also note that the section on Interfaces (https://golang.org/ref/spec#Interface_types) says:
> each method must have a unique non-blank name
So that interface isn't even valid go; the fact that the compiler apparently accepts it is a bug. Whichever package is declaring it really shouldn't be doing that.
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