Go 速查备忘单

package main

import "fmt"

func main() {
    fmt.Println("Hello, world!")
}

直接运行代码

$ go run hello.go
Hello, world!

在 Go Playground 在线环境 中在线体验

var s1 string
s1 = "Learn Go!"

# 一次性声明多个变量
var b, c int = 1, 2
var d = true

短变量简写语法 (:=)

s1 := "Learn Go!"        // string 类型推导
b, c := 1, 2             // int 类型推导
d := true                // bool 类型推导

参阅: 基础数据类型

package main

import "fmt"

// 程序的入口主函数
func main() {
    fmt.Println("Hello world!")
    say("Hello Go!")
}

func say(message string) {
    fmt.Println("输出消息: ", message)
}

参阅: 函数详解

// 单行注释

/* 多行
   注释 */

if true {
    fmt.Println("条件成立！")
}

参阅: 流程控制

s1 := "Hello" + "World"

s2 := `原始多行字符串字面量 (Raw string)
可以包含换行符。`

// 输出: 10 (字符串长度)
fmt.Println(len(s1))

// 输出: Hello (切片)
fmt.Println(string(s1[0:5]))

字符串在 Go 中属于 string 类型。

num := 3         // int 整型
num := 3.        // float64 浮点型
num := 3 + 4i    // complex128 复数型
num := byte('a') // byte (uint8 别名)

var u uint = 7        // uint 无符号整型
var p float32 = 22.7  // 32 位浮点数

#数值运算符 (Operators)

x := 5
x++
fmt.Println("x + 4 =", x + 4)
fmt.Println("x * 4 =", x * 4)

参阅: 运算符详解

isTrue   := true
isFalse  := false

#逻辑运算符

fmt.Println(true && true)   // true
fmt.Println(true && false)  // false
fmt.Println(true || true)   // true
fmt.Println(true || false)  // true
fmt.Println(!true)          // false

参阅: 运算符详解

func main () {
  b := *getPointer()
  fmt.Println("Value is", b)
}

func getPointer () (myPointer *int) {
  a := 234
  return &a
}

a := new(int)
*a = 234

See: Pointers

s := make([]string, 3)
s[0] = "a"
s[1] = "b"
s = append(s, "d")
s = append(s, "e", "f")

fmt.Println(s)
fmt.Println(s[1])
fmt.Println(len(s))
fmt.Println(s[1:3])

slice := []int{2, 3, 4}

See also: Slices example

const s string = "constant"
const Phi = 1.618
const n = 500000000
const d = 3e20 / n
fmt.Println(d)

i := 90
f := float64(i)
u := uint(i)

// Will be equal to the character Z
s := string(i)

#How to get int string?

i := 90

// need import "strconv"
s := strconv.Itoa(i)
fmt.Println(s) // Outputs: 90

package main

import (
	"fmt"
	s "strings"
)

func main() {
    /* Need to import strings as s */
	fmt.Println(s.Contains("test", "e"))

    /* Build in */
    fmt.Println(len("hello"))  // => 5
    // Outputs: 101
	fmt.Println("hello"[1])
    // Outputs: e
	fmt.Println(string("hello"[1]))

}

a := 10

if a > 20 {
    fmt.Println(">")
} else if a < 20 {
    fmt.Println("<")
} else {
    fmt.Println("=")
}

x := "hello go!"

if count := len(x); count > 0 {
    fmt.Println("Yes")
}

if _, err := doThing(); err != nil {
    fmt.Println("Uh oh")
}

x := 42.0
switch x {
case 0:
case 1, 2:
    fmt.Println("Multiple matches")
case 42:   // Don't "fall through".
    fmt.Println("reached")
case 43:
    fmt.Println("Unreached")
default:
    fmt.Println("可选")
}

See: Switch

for i := 0; i <= 10; i++ {
  fmt.Println("i: ", i)
}

nums := []int{2, 3, 4}
sum := 0
for _, num := range nums {
    sum += num
}
fmt.Println("sum:", sum)

i := 1
for i <= 3 {
    fmt.Println(i)
    i++
}

for i := 0; i <= 5; i++ {
    if i % 2 == 0 {
        continue
    }
    fmt.Println(i)
}

for {
    fmt.Println("loop")
    break
}

v := Vertex{X: 1, Y: 2}
// Field names can be omitted
v := Vertex{1, 2}
// Y is implicit
v := Vertex{X: 1}

You can also put field names.

v := &Vertex{1, 2}
v.X = 2

Doing v.X is the same as doing (*v).X, when v is a pointer.

func plus(a int, b int) int {
    return a + b
}
func plusPlus(a, b, c int) int {
    return a + b + c
}
fmt.Println(plus(1, 2))
fmt.Println(plusPlus(1, 2, 3))

func vals() (int, int) {
    return 3, 7
}

a, b := vals()
fmt.Println(a)    // => 3
fmt.Println(b)    // => 7

r1, r2 := func() (string, string) {
    x := []string{"hello", "qr.warpnav.com"}
    return x[0], x[1]
}()

// => hello qr.warpnav.com
fmt.Println(r1, r2)

func split(sum int) (x, y int) {
  x = sum * 4 / 9
  y = sum - x
  return
}

x, y := split(17)
fmt.Println(x)   // => 7
fmt.Println(y)   // => 10

Note that using naked returns hurts readability.

func sum(nums ...int) {
    fmt.Print(nums, " ")
    total := 0
    for _, num := range nums {
        total += num
    }
    fmt.Println(total)
}
sum(1, 2)     //=> [1 2] 3
sum(1, 2, 3)  // => [1 2 3] 6

nums := []int{1, 2, 3, 4}
sum(nums...)  // => [1 2 3 4] 10

import --> const --> var --> init()

var num = setNumber()

func setNumber() int {
    return 42
}
func init() {
    num = 0
}
func main() {
    fmt.Println(num) // => 0
}

func main() {
    // assign a function to a name
    add := func(a, b int) int {
        return a + b
    }
    // use the name to call the function
    fmt.Println(add(3, 4)) // => 7
}

func scope() func() int{
    outer_var := 2
    foo := func() int {return outer_var}
    return foo
}

// Outpus: 2
fmt.Println(scope()())

func outer() (func() int, int) {
    outer_var := 2
    inner := func() int {
        outer_var += 99
        return outer_var
    }
    inner()
    return inner, outer_var
}
inner, val := outer()
fmt.Println(inner()) // => 200
fmt.Println(val)     // => 101

package main

// An internal package may be imported only by another package
// that is inside the tree rooted at the parent of the internal directory
package internal

See: Internal packages

// Begin with a capital letter
func Hello () {
  ···
}

See: Exported names

ch <- 1
ch <- 2
ch <- 3
close(ch) // Closes a channel

// Iterate the channel until closed
for i := range ch {
  ···
}

// Closed if `ok == false`
v, ok := <- ch

See: Range and close

ch := make(chan int, 2)
ch <- 1
ch <- 2
ch <- 3
// fatal error:
// all goroutines are asleep - deadlock

See: Buffered channels

func main() {
  defer func() {
    fmt.Println("Done")
  }()
  fmt.Println("Working...")
}

func main() {
  var d = int64(0)
  defer func(d *int64) {
    fmt.Printf("& %v Unix Sec\n", *d)
  }(&d)
  fmt.Print("Done ")
  d = time.Now().Unix()
}

The defer func uses current value of d, unless we use a pointer to get final value at end of main.

func main() {
  defer fmt.Println("Done")
  fmt.Println("Working...")
}

See: Defer, panic and recover

• break
• default
• func
• interface
• select
• case
• defer
• go
• map
• struct
• chan
• else
• goto
• package
• switch
• const
• fallthrough
• if
• range
• type
• continue
• for
• import
• return
• var
• iota