If a variable should have a fixed value that cannot be changed, you can use the const keyword.
The const keyword declares the variable as "constant", which means that it is unchangeable and read-only .
Syntax
const
CONSTNAME type = valueNote
The value of a constant must be assigned when you declare it.
Declaring a Constant
Here is an example of declaring a constant in Go:
Example
package main
import ("fmt")
const PI = 3.14
func main() {
fmt.Println(PI)
}Constant Rules
- Constant names follow the same naming rules as variables
- Constant names are usually written in uppercase letters (for easy identification and differentiation from variables)
- Constants can be declared both inside and outside of a function
Constant Types
There are two types of constants
- Typed constants
- Untyped constants
Typed Constants
Typed constants are declared with a defined type:
Example
package main
import ("fmt")
const A int = 1
func main() {
fmt.Println(A)
}Untyped Constants
Untyped constants are declared without a type:
Example
package main
import ("fmt")
const A = 1
func main() {
fmt.Println(A)
}Note
In this case, the type of the constant is inferred from the value (means the compiler decides the type of the constant, based on the value).
Constants: Unchangeable and Read-only
When a constant is declared, it is not possible to change the value later:
Example
package main
import ("fmt")
func main() {
const A = 1
A = 2
fmt.Println(A)
}Multiple Constants Declaration
Multiple constants can be grouped together into a block for readability:
Example
package main
import ("fmt")
const ( A int = 1
B = 3.14
C = "Hi!" )
func main() {
fmt.Println(A)
fmt.Println(B)
fmt.Println(C)
}