Golang 备忘清单

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

直接运行

$ go run hello.go
Hello, world!

或者在 Go repl 中尝试一下

var s1 string
s1 = "Learn Go!"
// 一次声明多个变量
var b, c int = 1, 2
var d = true

简短声明

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

参见：基本类型

package main
import "fmt"
// 程序的入口点
func main() {
  fmt.Println("Hello world!")
  say("Hello Go!")
}
func say(message string) {
  fmt.Println("You said: ", message)
}

参见：函数(Functions)

// 单行注释
/* 这是
多行注释 */

if true {
  fmt.Println("Yes!")
}

参见：条件控制

s1 := "Hello" + "World"
s2 := `A "raw" string literal
can include line breaks.`
// 输出：11
fmt.Println(len(s1))
// 输出：Hello
fmt.Println(string(s1[0:5]))

字符串的类型为 字符串

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

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

a := new(int)
*a = 234

参见：指针(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}

另见：切片示例

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

package main
import (
	"fmt"
	s "strings"
)
func main() {
    /* 需要将字符串导入为 s */
	fmt.Println(s.Contains("test", "e"))
    /* 内置 */
    fmt.Println(len("hello"))  // => 5
    // 输出: 101
	fmt.Println("hello"[1])
    // 输出: e
	fmt.Println(string("hello"[1]))
}

实例	Result
Contains("test", "es")	true
Count("test", "t")	2
HasPrefix("test", "te")	true
HasSuffix("test", "st")	true
Index("test", "e")	1
Join([]string{"a", "b"}, "-")	a-b
Repeat("a", 5)	aaaaa
Replace("foo", "o", "0", -1)	f00
Replace("foo", "o", "0", 1)	f0o
Split("a-b-c-d-e", "-")	[a b c d e]
ToLower("TEST")	test
ToUpper("test")	TEST

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("Optional")
}

参见：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}

您还可以输入字段名

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", "world"}
    return x[0], x[1]
}()
// => hello world
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

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() {
  // 将函数赋给名称
  add := func(a, b int) int {
      return a + b
  }
  // 使用名称调用函数
  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
// 一个内部包只能被另一个包导入
// 那是在以内部目录的父级为根的树内
package internal

另见：内部包

// 以大写字母开头
func Hello () {
  ···
}

另见：导出的名称

ch <- 1
ch <- 2
ch <- 3
close(ch) // 关闭频道

---

// 迭代通道直到关闭
for i := range ch {
  ···
}

---

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

参见：范围和关闭

ch := make(chan int, 2)
ch <- 1
ch <- 2
ch <- 3
// 致命错误：
// 所有 goroutine 都处于休眠状态 - 死锁

参见：缓冲通道

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()
}

defer 函数使用当前值d，除非我们使用指针在 main 末尾获取最终值

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

参见：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

+	&	+=	&=	&&	==	!=	(	)
-	|	-=	|=	||	<	<=	[	]
*	^	*=	^=	<-	>	>=	{	}
/	<<	/=	<<=	++	=	:=	,	;
%	>>	%=	>>=	--	!	...	.	:
	&^	&^=