Untyped Numeric Constants in Go

When you write a constant without an explicit type, Go can use its value in more than one numeric context. The value must fit the destination type, but you do not need a conversion just because the destinations have different numeric types. in The Golang Official Documentation

package main
 
import "fmt"
 
func main() {
	const initial = 65
	var small byte = initial
	var large int64 = initial
	fmt.Printf("%v %T\n", small, small)
	fmt.Printf("%v %T\n", large, large)
}

If you’ll run it with go run main.go, you’ll get:

65 uint8
65 int64

initial is the untyped value 65. That value fits in a byte and in an int64, so both declarations work. Printing %T shows that small is a uint8 (the type named by byte) and large is an int64. The constant did not force both variables to have the same type.