5-value-types

README

Golang Basic Value Types

Go's basic types 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

The example shows variables of several types, and also that variable declarations may be "factored" into blocks, as with import statements.

The int, uint, and uintptr types are usually 32 bits wide on 32-bit systems and 64 bits wide on 64-bit systems. When you need an integer value you should use int unless you have a specific reason to use a sized or unsigned integer type.

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)
	fmt.Printf("Type: %T Value: %v\n", MaxInt, MaxInt)
	fmt.Printf("Type: %T Value: %v\n", z, z)
}

Edit & Run go run valuetypes.go on this directory and observe the results.

Type conversions

The expression T(v) converts the value v to the type T.

Some numeric conversions:

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

Or, put more simply:

i := 42
f := float64(i)
u := uint(f)

Unlike in C, in Go assignment between items of different type requires an explicit conversion. Try removing the float64 or uint conversions in the example and see what happens.

package main

import (
	"fmt"
	"math"
)

func main() {
	var x, y int = 3, 4
	var f float64 = math.Sqrt(float64(x*x + y*y))
	var z uint = uint(f)
	fmt.Println(x, y, z)
}

Type inference

When declaring a variable without specifying an explicit type (either by using the := syntax or var = expression syntax), the variable's type is inferred from the value on the right hand side.

When the right hand side of the declaration is typed, the new variable is of that same type:

var i int
j := i // j is an int

But when the right hand side contains an untyped numeric constant, the new variable may be an int, float64, or complex128 depending on the precision of the constant:

i := 42           // int
f := 3.142        // float64
g := 0.867 + 0.5i // complex128

Try changing the initial value of v in the example code and observe how its type is affected.

package main

import "fmt"

func main() {
	v := 42 // change me!
	fmt.Printf("v is of type %T\n", v)
}

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