A constant, or const, is like a variable whose value can't change while the program is running. To define constants in Go, we use const along with the name and value we want.

package main

import "log"

const name = "test"

func main(){
    log.Println(name)
}

Constants can have whatever type we want. In the example below, we define a constant with type string:

package main

import "log"

// defining a constant with string type
const name string = "test"

func main() {
    log.Printf("data type is: %T and value is: %v", name, name)
}

If we specify a data type for a const, we can only use that const in ways that respect that data type:

package main

import "log"

const minuteSeconds = 60 // a constant with no data type

const dayHours int = 24 // a constant with a data type

func main() {
	var (
		x int
		y int32
	)

	x = minuteSeconds
	y = minuteSeconds

	log.Println(x, y)

	x = dayHours
	y = dayHours // this line will fail

	log.Println(x, y)
}

In the code above, we can see that the value of the constant minuteSeconds can be stored in both the x and y variables, because it has no data type. But the constant dayHours has type int, so its value can't be stored in variable y, because that variable has type int32.

Summary

In this part, we got familiar with const. We saw that you can specify a constant's type, which makes it behave differently when it's used.

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