_(underscore) in Golang is called Blank Identifier . Identifier is a user-defined name of program elements used for identification purposes.
Golang has a special feature of defining and using unused variables using Blank Identifier. Unused variables are those variables that are defined by the user during the program but he never uses them. These variables make the program almost unreadable. As you know, Golang is a more concise and readable programming language so it does not allow the programmer to define an unused variable. If you do so, the compiler will give you an error.
The real use of Blank Identifier comes when a function returns multiple values, but we only need a few values and need to get rid of the extra ones. It basically tells the compiler that this variable is not needed and ignores it without any error. It hides the values of the variable and makes the program readable. So whenever you assign a value to Blank Identifier, it will not be used.
Example 1: In the program below, the function mul_div returns two values and we store both values in mul and div identifiers . But in the entire program, we are using only one variable i.e. mul . So, the compiler will throw an error that div is declared and not used.
// Chương trình Go hiện trình biên dịch
// báo lỗi nếu một biến
// được khai báo nhưng không được sử dụng
package main
import "fmt"
// Hàm chính
func main() {
// gọi hàm này
// hàm trả về hai giá trị được gán
// cho định danh mul và div
mul, div := mul_div(105, 7)
// chỉ dùng biến mul
// trình biên dịch sẽ báo lỗi
fmt.Println("105 x 7 = ", mul)
}
// hàm trả về hai
// giá trị của kiểu integer
func mul_div(n1 int, n2 int) (int, int) {
// trả về các giá trị này
return n1 * n2, n1 / n2
}
Result:
./prog.go:15:7: div được khai báo nhưng không được dùngExample 2: Use the Blank identifier to fix the above program. Instead of the div identifier, just use _ (underscore) . It allows the compiler to ignore the declaration error and not use it for that particular variable.
// Chương trình Go dùng định danh trống
package main
import "fmt"
// Hàm chính
func main() {
// gọi hàm này
// hàm trả về hai giá trị
// được gán cho định danh mul và trống
mul, _ := mul_div(105, 7)
// chỉ dùng biến mul
fmt.Println("105 x 7 = ", mul)
}
// hàm trả về hai giá trị
// của kiểu integer
func mul_div(n1 int, n2 int) (int, int) {
// trả về giá trị này
return n1 * n2, n1 / n2
}
Result:
105 x 7 = 735Important points to remember:
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