Three uses of golang underscores

1. Ignore return value

This should be the simplest use , For example, a function returns three parameters , But we only need two of them , Another parameter can be ignored , So the code can be written like this ：

v1, v2, _ := function(...)

2. Used in variables ( In particular, interface assertions )

For example, we define an interface (interface)：

type Food interface {
    
     Eat()
}

Then a structure is defined (struct)

type Water struct {
    
}

Then we want to judge in the code Water This struct Is it implemented Food This interface

var _ Food = Water{
    }

The above is used to judge Water Is it implemented Food, Used as a type assertion , If Water It didn't come true Food, Compile error will be reported

3. Use in import package

Suppose we are in the code import In this way package ：

import _ "test/food"

This means that... Will be called before executing this code test/food Initialization functions in (init), In this way, only the imported package is initialized , Instead of using other functions in the package
So let's say we define one Food struct, Then initialize it

package food
import "fmt"
type Food struct {
    
        Id   int
        Name string
}
func init() {
    
        f := &Food{
    Id: 123, Name: "apple"}
        fmt.Printf("init foo object: %v\n", f)
}

And then in main Introduce... Into the function test/food

package main
import (
        "fmt"
        _ "test/food"
)
func main() {
    
        fmt.Printf("hello world\n")
}

The operation results are as follows

init food object: &{
    123 apple}
hello world

We can see ： stay main Output function ”hello world” I've been right before food object It's initialized （ Is loaded test/food Of documents init() Method ）！