Table of Contents

Overview

Numeric constant in go are further divided into three types

Integer
Floats
Complex Numbers

To better understand numeric 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 numeric as well.

A untyped integer constant (both named and unnamed) can be assigned to int types, float types and complex . This is because an int value can be int or float or complex. For eg int value 123 can be

A int whose value is 123
A float whose value is 123.0
A complex whose imaginary part is 0

On the basis of similar logic a untyped float constant can be assigned to all floats and complex types but not integer because for eg a float 5.3 cannot be an integer.

On the basis of similar logic a untyped comple constant can be assigned to complex types but not integer and float because for eg a float 5i+3 cannot be an integer or a float

Let’s see a program to understand it

Example

See below program illustrating the above point. In the program we have example for

Typed integer constant
Untyped unnamed integer constant
Untyped named integer constant

package main

import "fmt"

func main() {
	//Typed int constant
	const aa int = 123
	var uu = aa
	fmt.Println("Typed named integer constant")
	fmt.Printf("uu: Type: %T Value: %v\n\n", uu, uu)

	//Below line will raise a compilation error
	//var v int32 = aa

	//Untyped named int constant
	const bb = 123
	var ww = bb
	var xx int32 = bb
	var yy float64 = bb
	var zz complex128 = bb
	fmt.Println("Untyped named integer constant")
	fmt.Printf("ww: Type: %T Value: %v\n", ww, ww)
	fmt.Printf("xx: Type: %T Value: %v\n", xx, xx)
	fmt.Printf("yy: Type: %T Value: %v\n", yy, yy)
	fmt.Printf("zz: Type: %T Value: %v\n\n", zz, zz)

	//Untyped unnamed int constant
	var ll = 123
	var mm int32 = 123
	var nn float64 = 123
	var oo complex128 = 123
	fmt.Println("Untyped unnamed integer constant")
	fmt.Printf("ll: Type: %T Value: %v\n", ll, ll)
	fmt.Printf("mm: Type: %T Value: %v\n", mm, mm)
	fmt.Printf("nn: Type: %T Value: %v\n", nn, nn)
	fmt.Printf("oo: Type: %T Value: %v\n", oo, oo)
}

Output

Typed named integer constant
uu: Type: int Value: 123

Untyped named integer constant
ww: Type: int Value: 123
xx: Type: int32 Value: 123
yy: Type: float64 Value: 123
zz: Type: complex128 Value: (123+0i)

Untyped unnamed integer constant
ll: Type: int Value: 123
mm: Type: int32 Value: 123
nn: Type: float64 Value: 123
oo: Type: complex128 Value: (123+0i)

Now above program shows example of a

Typed integer constant
Untyped unnamed integer constant
Untyped named integer constant

Let’s understand each of them and their behaviour

Typed integer constant

It is defined as below

const aa int = 123

Typed integer constant can be assigned to a variable created with var keyword like below

var uu = aa

It will raise compilation error when assigned to another int type. So below raises compilation error as aa variable is already of type int

var v int32 = aa

Untyped named integer constant

It is defined as below

const bb = 123

Untyped named integer constant can be assigned to any int type, any float type and any complex number type and also to any variable created with var keyword. So below works

var ww = bb
var xx int32 = bb
var yy float64 = bb
var zz complex128 = bb

Untyped unnamed integer constant

It is as below

Untyped named integer constant can be assigned to any int type, any float type and any complex number type and also to any variable created with var keyword. So below works

var ww = 123
var xx int32 = 123
var yy float64 = 123
var zz complex128 = 123

Numeric Expressions

Due to untyped nature of constant numeric constants, different numeric constant type can be mixed and matched up to form a expression

package main
import "fmt"
func main() {
    var p = 5.2 / 3
    fmt.Printf("p: Type: %T Value: %v\n", p, p)
}

Output:

p: Type: float64 Value: 1.7333333333333334

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