hello.go

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

直接运行

$ go run hello.goHello, world!

或者在 Go repl 中尝试一下

变量

var s1 strings1 = "Learn Go!"// 一次声明多个变量var b, c int = 1, 2var d = true

简短声明

s1 := "Learn Go!"        // stringb, c := 1, 2             // intd := true                // bool

参见：基本类型

函数

package mainimport "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)

注释

// 单行注释/* 这是多行注释 */

如果语句

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

参见：条件控制

Golang 基本类型

字符串 Strings

s1 := "Hello" + "World"s2 := `A "raw" string literalcan include line breaks.`// 输出：10fmt.Println(len(s1))// 输出：Hellofmt.Println(string(s1[0:5]))

字符串的类型为 字符串

数字 Numbers

num := 3             // intnum := 3.            // float64num := 3 + 4i        // complex128num := byte('a')     // byte (alias: uint8)var u uint = 7       // uint (unsigned)var p float32 = 22.7  // 32-bit float

操作符 Operators

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

参见：更多操作符

布尔值 Booleans

isTrue   := trueisFalse  := false

操作符

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

参见：更多操作符

数组 Arrays

┌────┬────┬────┬────┬─────┬─────┐| 2  | 3  | 5  | 7  | 11  | 13  |└────┴────┴────┴────┴─────┴─────┘  0    1    2    3     4     5

primes := [...]int{2, 3, 5, 7, 11, 13}fmt.Println(len(primes)) // => 6// 输出：[2 3 5 7 11 13]fmt.Println(primes)// 与 [:3] 相同，输出：[2 3 5]fmt.Println(primes[0:3])

var a [2]stringa[0] = "Hello"a[1] = "World"fmt.Println(a[0], a[1]) //=> Hello Worldfmt.Println(a)   // => [Hello World]

2d array

var twoDimension [2][3]intfor i := 0; i < 2; i++ {    for j := 0; j < 3; j++ {        twoDimension[i][j] = i + j    }}// => 2d:  [[0 1 2] [1 2 3]]fmt.Println("2d: ", twoDimension)

指针(Pointers)

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)

切片(Slices)

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

常量(Constants)

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

类型转换

i := 90f := float64(i)u := uint(i)// 将等于字符Zs := string(i)

如何获取int字符串？

i := 90// 需要导入“strconv”s := strconv.Itoa(i)fmt.Println(s) // Outputs: 90

Golang 字符串

字符串函数

package mainimport (	"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]))}

fmt.Printf

package mainimport (	"fmt"	"os")type point struct {	x, y int}func main() {	p := point{1, 2}	fmt.Printf("%v\n", p)                        // => {1 2}	fmt.Printf("%+v\n", p)                       // => {x:1 y:2}	fmt.Printf("%#v\n", p)                       // => main.point{x:1, y:2}	fmt.Printf("%T\n", p)                        // => main.point	fmt.Printf("%t\n", true)                     // => TRUE	fmt.Printf("%d\n", 123)                      // => 123	fmt.Printf("%b\n", 14)                       // => 1110	fmt.Printf("%c\n", 33)                       // => !	fmt.Printf("%x\n", 456)                      // => 1c8	fmt.Printf("%f\n", 78.9)                     // => 78.9	fmt.Printf("%e\n", 123400000.0)              // => 1.23E+08	fmt.Printf("%E\n", 123400000.0)              // => 1.23E+08	fmt.Printf("%s\n", "\"string\"")             // => "string"	fmt.Printf("%q\n", "\"string\"")             // => "\"string\""	fmt.Printf("%x\n", "hex this")               // => 6.86578E+15	fmt.Printf("%p\n", &p)                       // => 0xc00002c040	fmt.Printf("|%6d|%6d|\n", 12, 345)           // => |    12|   345|	fmt.Printf("|%6.2f|%6.2f|\n", 1.2, 3.45)     // => |  1.20|  3.45|	fmt.Printf("|%-6.2f|%-6.2f|\n", 1.2, 3.45)   // => |1.20  |3.45  |	fmt.Printf("|%6s|%6s|\n", "foo", "b")        // => |   foo|     b|	fmt.Printf("|%-6s|%-6s|\n", "foo", "b")      // => |foo   |b     |	s := fmt.Sprintf("a %s", "string")	fmt.Println(s)	fmt.Fprintf(os.Stderr, "an %s\n", "error")}

另见：fmt

函数实例

Golang 条件控制

有条件的

a := 10if a > 20 {    fmt.Println(">")} else if a < 20 {    fmt.Println("<")} else {    fmt.Println("=")}

if 中的语句

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

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

Switch

x := 42.0switch 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 loop

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

对于 Range 循环

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

While 循环

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

Continue 关键字

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

Break 关键字

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

Golang 结构和映射

定义

package mainimport (	"fmt")type Vertex struct {	X int	Y int}func main() {	v := Vertex{1, 2}	v.X = 4	fmt.Println(v.X, v.Y) // => 4 2}

参见：结构(Structs)

字面量

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

您还可以输入字段名

映射

m := make(map[string]int)m["k1"] = 7m["k2"] = 13fmt.Println(m) // => map[k1:7 k2:13]v1 := m["k1"]fmt.Println(v1)     // => 7fmt.Println(len(m)) // => 2delete(m, "k2")fmt.Println(m) // => map[k1:7]_, prs := m["k2"]fmt.Println(prs) // => falsen := map[string]int{"foo": 1, "bar": 2}fmt.Println(n) // => map[bar:2 foo:1]

指向结构的指针

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

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

Golang 函数

多个参数

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))

多次返回

func vals() (int, int) {  return 3, 7}a, b := vals()fmt.Println(a)    // => 3fmt.Println(b)    // => 7

匿名函数

r1, r2 := func() (string, string) {    x := []string{"hello", "world"}    return x[0], x[1]}()// => hello worldfmt.Println(r1, r2)

命名返回

func split(sum int) (x, y int) {  x = sum * 4 / 9  y = sum - x  return}x, y := split(17)fmt.Println(x)   // => 7fmt.Println(y)   // => 10

变量函数

func sum(nums ...int) {  fmt.Print(nums, " ")  total := 0  for _, num := range nums {      total += num  }  fmt.Println(total)}sum(1, 2)     //=> [1 2] 3sum(1, 2, 3)  // => [1 2 3] 6nums := []int{1, 2, 3, 4}sum(nums...)  // => [1 2 3 4] 10

初始化函数

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

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

作为值的函数

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}

关闭 1

func scope() func() int{  outer_var := 2  foo := func() int {return outer_var}  return foo}// Outpus: 2fmt.Println(scope()())

关闭 2

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()) // => 200fmt.Println(val)     // => 101

Golang 包(Packages)

导入

import "fmt"import "math/rand"

等同于

import (  "fmt"        // 给 fmt.Println  "math/rand"  // 给 rand.Intn)

另见：导入

别名

import r "math/rand"

import (    "fmt"    r "math/rand")

r.Intn()

Packages

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

导出名称

// 以大写字母开头func Hello () {  ···}

另见：导出的名称

Golang 并发

协程

package mainimport (	"fmt"	"time")func f(from string) {	for i := 0; i < 3; i++ {		fmt.Println(from, ":", i)	}}func main() {	f("direct")	go f("goroutine")	go func(msg string) {		fmt.Println(msg)	}("going")	time.Sleep(time.Second)	fmt.Println("done")}

参见：Goroutines, Channels

WaitGroup

package mainimport (	"fmt"	"sync"	"time")func w(id int, wg *sync.WaitGroup) {	defer wg.Done()	fmt.Printf("%d starting\n", id)	time.Sleep(time.Second)	fmt.Printf("%d done\n", id)}func main() {	var wg sync.WaitGroup	for i := 1; i <= 5; i++ {		wg.Add(1)		go w(i, &wg)	}	wg.Wait()}

参见：WaitGroup

Closing channels

ch <- 1ch <- 2ch <- 3close(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

缓冲通道

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

参见：缓冲通道

Golang 错误控制

延迟函数

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

Lambda defer

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

Defer

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

参见：Defer, panic and recover

Golang 方法(Methods)

接收器

type Vertex struct {  X, Y float64}func (v Vertex) Abs() float64 {  return math.Sqrt(v.X * v.X + v.Y * v.Y)}v := Vertex{1, 2}v.Abs()

参见：Methods

Mutation

func (v *Vertex) Scale(f float64) {  v.X = v.X * f  v.Y = v.Y * f}v := Vertex{6, 12}v.Scale(0.5)// `v` 已更新

参见：指针接收器

Golang 接口(Interfaces)

基本接口(Interfaces)

type Shape interface {  Area() float64  Perimeter() float64}

结构(Struct)

type Rectangle struct {  Length, Width float64}

结构 Rectangle 通过实现其所有方法隐式实现接口 Shape

方法(Methods)

func (r Rectangle) Area() float64 {  return r.Length * r.Width}func (r Rectangle) Perimeter() float64 {  return 2 * (r.Length + r.Width)}

在 Shape 中定义的方法在Rectangle中实现

接口实例

func main() {  var r Shape = Rectangle{Length: 3, Width: 4}  fmt.Printf("Type of r: %T, Area: %v, Perimeter: %v.", r, r.Area(), r.Perimeter())}

杂项

关键字(Keywords)

• 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

运算符和标点符号

另见

• Devhints (devhints.io)
• A tour of Go (tour.golang.org)
• Golang wiki (github.com)
• Effective Go (golang.org)
• Go by Example (gobyexample.com)
• Awesome Go (awesome-go.com)
• JustForFunc Youtube (youtube.com)
• Style Guide (github.com)