Golang provides the mechanism to set default values for declared variables.

How does it work?

When we declare a variable without explicit initialization, Golang will allocate memory for such a variable by setting a zero value for it.

var var1 bool
var var2 int
var var3 float64
var var4 string
var var5 *int
var var6 []int
var var7 map[int]string

Let’s see what values are set for the particular variables listed above:

fmt.Printf("%T -> %#v\n", var1, var1)
fmt.Printf("%T -> %#v\n", var2, var2)
fmt.Printf("%T -> %#v\n", var3, var3)
fmt.Printf("%T -> %#v\n", var4, var4)
fmt.Printf("%T -> %#v\n", var5, var5)
fmt.Printf("%T -> %#v\n", var6, var6)
fmt.Printf("%T -> %#v\n", var7, var7)


bool -> false
int -> 0
float64 -> 0
string -> ""
*int -> (*int)(nil)
[]int -> []int(nil)
map[int]string -> map[int]string(nil)

As you can see for the primitive types like bool, numeric and string the zero value is false, 0 or "" respectively, but for more complex types it’s nil.

This mechanism works recursively, so elements in an array or fields in a struct will be zeroed too (if no value during the initialization is given).

type Example struct {
    name string
    num int
    p *int

var var8 Example
fmt.Printf("%T -> %#v\n", var8, var8)


main.Example -> main.Example{name:"", num:0, p:(*int)(nil)}


When we declare a variable the allocated memory gets initialized at least to its zero value state.