Overview

There are two untyped boolean constant true and false.  Below is the program illustrating a boolean constant. 

To better understand boolean constant in golang it is important to understand typed and untyped constant in go. Please refer to this article for that – https://golangbyexample.com/typed-untyped-constant-golang/

Once you have gone through the article you would have understood that constant can be declared in three ways

• Typed  constant
• Untyped unnamed  constant
• Untyped named constant

It is the same case with boolean as well. Let’s see a program to understand it

Example

package main

import "fmt"

func main() {
	type myBool bool

	//Typed Boolean constant
	const aa bool = true
	var uu = aa
	fmt.Println("Typed named boolean constant")
	fmt.Printf("uu: Type: %T Value: %v\n\n", uu, uu)

	//Below line will raise a compilation error
	//var vv myBool = aa

	//Untyped named boolean constant
	const bb = true

	var ww myBool = bb
	var xx = bb
	fmt.Println("Untyped named boolean constant")
	fmt.Printf("ww: Type: %T Value: %v\n", ww, ww)
	fmt.Printf("xx: Type: %T Value: %v\n\n", xx, xx)

	//Untyped unnamed boolean constant
	var yy myBool = true
	var zz = true
	fmt.Println("Untyped unnamed boolean constant")
	fmt.Printf("yy: Type: %T Value: %v\n", yy, yy)
	fmt.Printf("zz: Type: %T Value: %v\n", zz, zz)
}

Output:

Typed named boolean constant
uu: Type: bool Value: true

Untyped named boolean constant
ww: Type: main.myBool Value: true
xx: Type: bool Value: true

Untyped unnamed boolean constant
yy: Type: main.myBool Value: true
zz: Type: bool Value: true

In the above program, we created a new type myBool

type myBool bool

Also above program shows the example of

• Typed boolean constant
• Untyped unnamed boolean constant
• Untyped named boolean constant

Let’s understand each of them and their behaviour

Typed boolean constant

It is defined as below

const aa bool = true

Notice in above that below line will cause a compilation error. This is because variable aa is of typed boolean constant . So below line will cause compilation error as it cannot be assigned to variable of type myBool

var v mybool = aa

But typed string constant can be assigned to a variable created with var keyword like below

var uu = aa

Untyped named boolean constant

It is defined as below

const bb = true

Untyped named string constant can be assigned to variable of type myBool as well variable created with var keyword because it is untyped so type of the constant will be decided depending upon the type of variable they are being assigned to.

var ww mybool = bb
var xx = bb

Untyped unnamed boolean constant

It is like below

true

Untyped unnamed string constant can be assigned to variable of type myBool as well variable created with var keyword because it is untyped so type of the constant will be decided depending upon the type of variable they are being assigned to.

var yy mybool = true
var zz = true