The blank identifier has many possible uses, but its main purpose is to allow discarding returns from functions that have multiple returns:
// We only care about the rune and possible error, not its length
r, _, err := buf.ReadRune()There are some other fun, but sometimes hackish, uses.
Mark an import or local variable as "used" so that the compiler won't issue an error:
import "fmt"
var _ = fmt.Println // now fmt is used and the compiler won't complain
func main() {
var x int
_ = x // now x is used and the compiler won't complain
}Make sure a type implements an interface at compile time:
var _ InterfaceType = Type{} // or new(Type), or whateverEnsure that a constant lies within a certain range at compile time:
// Ensure constVal <= 10
const _ uint = 10 - constVal
// Ensure constVal >= 1 (constVal > UINT_MAX + 1 is also an error)
const _ uint = -1 + constValEnsure a function parameter is unused:
// This could be useful if somebody wants a value of type
// func(int, int) int
// but you don't want the second parameter.
func identity(x, _ int) int { return x }golang
sql/driver 里面有使用:type noRows struct{}
var _ Result = noRows{}这个就是让编译器静态的检查一个类型是否实现某个接口,这是一种编程技巧.golang的接口是duck模型的,没有显示的声明,某个具体类型松散的实现某个接口,通过这层检查,基本上我们就可以确定某个具体类型实现了某个接口.这也是golang
duck接口模型的一个不好的点吧.这是一种辅助编程,加强程序健壮性的手段,理论上不使用这种方法,通过unit test也能保证．Some
people use a line like as an interface check. This line ensures that the type noRows implements
the Result interface.
If it doesn't you will get a compiler error.
