Variables and Types

Variables are declared using the var keyword or using the initial assignment operator := (only inside functions). The type of the variable comes last, and can be inferred if using the assignment operator. Variables can be at the package or function level. You can also declare constants with the const keyword, but cannot use the := operator. Numeric constants can be used for high precision.

package main

import "fmt"

var c, python, java bool

func main() {
	var i int
    j := 3 // int inferred
    const k = "Can't change this"
    const Big = 1 << 100 // 1 shifted left 100 times
	fmt.Println(i, c, python, java)
}

Types

The basic types in go are:

• bool
• string
• int, int8, int16, int32, int64
• uint, uint8, uint16, uint32, uint64, uintptr
• byte (alias for uint8)
• rune (alias for int32, represents a Unicode code point)
• float32, float64
• complex64, complex128

package main

import (
	"fmt"
	"math/cmplx"
)

var (
	ToBe   bool       = false
	MaxInt uint64     = 1<<64 - 1
	z      complex128 = cmplx.Sqrt(-5 + 12i)
)

func main() {
	fmt.Printf("Type: %T Value: %v\n", ToBe, ToBe) // bool, false
	fmt.Printf("Type: %T Value: %v\n", MaxInt, MaxInt) // uint64, 18446744073709551615
	fmt.Printf("Type: %T Value: %v\n", z, z) // complex128, (2+3i)
}

Default Values (Zero values)

When not given an initial value, the below types default to:

• bool - false
• string - ""
• numeric - 0

Type Conversion

You can cast variables to different types by specifying the type in the below syntax.

var i int = 42
var f float64 = float64(i)
var u uint = uint(f)

Generic Types

Types can also be generic to work with multiple different types of arguments.

// Singly linked list
type Node[T any] struct {
	next *Node[T]
	val  T
}