Default Types of Untyped Constants in Go

An untyped constant can take a type from its destination. But with a declaration such as count := 10, there is no destination type written down. In that situation Go uses the constant’s default type. in source

package main
 
import "fmt"
 
func main() {
	count := 10
	ratio := 1.5
	letter := 'A'
	ready := true
	name := "Go"
	number := 1 + 2i
	fmt.Printf("%T %T %T %T %T %T\n", count, ratio, letter, ready, name, number)
}

if you’ll run this, you’ll get int float64 int32 bool string complex128

The output shows those defaults in order. An integer literal becomes int, a floating-point literal becomes float64, a rune literal becomes rune (int32), a boolean becomes bool, a string becomes string, and a complex literal becomes complex128.

%T prints the resulting variable type, which is why the output says int32 for letter: rune is an alias for int32. Once each variable is declared, its type is fixed like any other variable’s type.