Go Constants

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Go Constants

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 = value

Note: 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)
}

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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)
}

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Untyped Constants

Untyped constants are declared without a type:

Example

package main
import ("fmt")

const A = 1

func main() {
fmt.Println(A)
}

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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)
}

Result:


        ./prog.go:8:7: cannot assign to A

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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)
}

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