Constants in

About Constants

Constants in Go are simple, unchanging values created with the const keyword. Constants may be given an explicit type:

const hi string = "hi" // string

or an implicit, default type:

const hello = "hello" // string

when the variable needs a type. This gives constants more flexibility in Go's type system and allows them to work in a variety of contexts without triggering a compiler error:

const number2 = 2 // 2 is an untyped numeric constant and does not need to be explicitly given the type float64 as required by the Sqrt method
sqrt2 := math.Sqrt(number2)

Go does not have enums like some other languages but the iota enumerator can be used to create successive untyped integer constants:

const (
    a = 6 * iota // 0
    b            // 6
    c            // 12
    d            // 18
)

Complex types like maps and slices are mutable and cannot be constants; the compiler will throw errors:

func main() {
    const m = map[int]int{2: 8}
    const s = []string{"exercism", "v3"}
}
// => const initializer map[int]int literal is not a constant
// => const initializer []string literal is not a constant

For a fuller explanation please see the resources here, here, and here.