Packages, variables and functions
Download
In my case, installed go1.14.darwin-amd64.pkg
Sample code
hello.go
package main
import "fmt"
func main() {
fmt.println("hello, world")
}
Test your Installation
$ go build hello.go # build
$ ./hello # run
# hello, world
Go tour
Go tour?
A guide program on how to use go.
$ go get golang.org/x/tour
After above command, you can find tour
in go/bin/. Double click to run.
Tour > Basics > Packages, variables and functions.
Packages
package main
import (
"fmt"
"math/rand"
)
func main() {
fmt.println(rand.Intn(10))
}
Every Go program is made of packages.
Programs start running in package
main
Imports can also be in multiple import statements.
import "fmt" import "math"
Exported names
fmt.Println(math.pi) // cannot refer to unexported name math.pi
fmt.Println(math.Pi) // 3.141592653589793
When importing a package, you can only accessible to its Exported names
. Which begins with a capital letter i.e., Pi
Functions
// Basic
func add(x int, y int) int {
return x + y
}
// You can omit the type if function parameters has same type
func add(x, y int) { ... }
// Multiple result
// Simply exchange the positions of x and y
func swap(x, y string) (string, string) {
return y, x
}
func main() {
a, b := swap("world", "hello")
fmt.Println(a, b) // "Hello World"
}
// Named return values
func split(sum int) (x, y int) {
x = sum * 4 / 9
y = sum - x
return
}
func main() {
fmt.Println(split(17)) // 7 10
}
Variables
// A var statement can be at package or function level
var i, j bool
var some_var // don't use underscore in Go names; var some_var should be someVar
func main() {
var i int
}
// Variables with initializers
var i, j int = 1, 2
// Short variable declarations
// := construct is not available outside a function
k := 3
Basic types
// Variable declaration can be "factored" into blocks like this
var (
ToBe bool = false
MaxInt uint = 1<<64 - 1
z complex128 = cmplx.Sqrt(-5 + 12i)
)
Zero value
Variables declared without an explicit value are given intial value. this is called zero
value.
var i int
var f float64
var b bool
var s string
fmt.Printf("%v %v %v %q\n", i, f, b, s)
// 0 0 false ""
Type conversions
The expression T(v) converts the value v to the type T.
var x = 3
var y float64 = math.Sqrt(float64(x))
var z float64 = math.Sqrt(x) // cannot use x as typeof float64..
Type inference
The variable's type is inferred from the value on the right hand side.
i := 3 // becomes int
f := 3.14 // becomes float64
g := 0.993 + 0.5i // becomes complexx128
Constants
Constant cannot be declared using :=
syntax.
const World = "世界"
// Numeric Constants (high-precision values)
const (
Big = 1 << 100
)
For more insights
Last updated
Was this helpful?