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Go - Zero Values

Each type in Go has a default value known as the zero value.

Basic Types

If a variable is declared but not initialized it takes on its zero value.

go
// Numeric types (Zero value: 0).
var n1 int     // 0
var n2 float32 // 0
var n3 float64 // 0
var n4 byte    // 0 (alias for uint8)
var n5 rune    // 0 (alias for int32)
// Booleans.
var b bool     // false
// Strings.
var s string   // "" (empty string)

Reference Types

The zero value is nil for slices, maps, pointers, functions, channels and interfaces:

go
// Slices.
var s []int          // nil
// Maps.
var m map[string]int // nil
// Pointers.
var p1 *int          // nil
var p2 *float64      // nil
// Functions.
var f func()         // nil
// Channels.
var c chan int       // nil
// Interfaces.
var i1 interface{}   // nil
var i2 any           // nil (any is an alias for interface{}, added in Go v1.18)
type I interface {
  M()
}
var i3 I             // nil

Struct Type

The zero value for a struct type is a struct value with all the fields set to their zero values:

go
type Person struct {
	Name string
	Age  int
}
var p Person // Person{Name: "", Age: 0}
p.Name       // "" (empty string)
p.Age        // 0