hello.go
package main
import "fmt"
func main() {
fmt.Println("Hello, world!")
}
直接運作
$ go run hello.go
Hello, world!
或者在 Go repl 中嘗試一下
變量
var s1 string
s1 = "Learn Go!"
// 一次聲明多個變量
var b, c int = 1, 2
var d = true
簡短聲明
s1 := "Learn Go!" // string
b, c := 1, 2 // int
d := true // bool
參見：基本類型
函數
package main
import "fmt"
// 程式的入口點
func main() {
fmt.Println("Hello world!")
say("Hello Go!")
}
func say(message string) {
fmt.Println("You said: ", message)
}
參見：函數(Functions)
注釋
// 單行注釋
/* 這是
多行注釋 */
如果語句
if true {
fmt.Println("Yes!")
}
參見：條件控制
Golang 基本類型
字元串 Strings
s1 := "Hello" + "World"
s2 := `A "raw" string literal
can include line breaks.`
// 輸出：10
fmt.Println(len(s1))
// 輸出：Hello
fmt.Println(string(s1[0:5]))
字元串的類型為 字元串
數字 Numbers
num := 3 // int
num := 3. // float64
num := 3 + 4i // complex128
num := byte('a') // byte (alias: uint8)
var u uint = 7 // uint (unsigned)
var p float32 = 22.7 // 32-bit float
操作符 Operators
x := 5
x++
fmt.Println("x + 4 =", x + 4)
fmt.Println("x * 4 =", x * 4)
參見：更多操作符
布爾值 Booleans
isTrue := true
isFalse := false
操作符
fmt.Println(true && true) // true
fmt.Println(true && false) // false
fmt.Println(true || true) // true
fmt.Println(true || false) // true
fmt.Println(!true) // false
參見：更多操作符
數組 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
// 輸出：[2 3 5 7 11 13]
fmt.Println(primes)
// 與 [:3] 相同，輸出：[2 3 5]
fmt.Println(primes[0:3])
var a [2]string
a[0] = "Hello"
a[1] = "World"
fmt.Println(a[0], a[1]) //=> Hello World
fmt.Println(a) // => [Hello World]
2d array
var twoDimension [2][3]int
for 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)
指針(Pointers)
func main () {
b := *getPointer()
fmt.Println("Value is", b)
}
func getPointer () (myPointer *int) {
a := 234
return &a
}
a := new(int)
*a = 234
參見：指針(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}
另見：切片示例
常量(Constants)
const s string = "constant"
const Phi = 1.618
const n = 500000000
const d = 3e20 / n
fmt.Println(d)
類型轉換
i := 90
f := float64(i)
u := uint(i)
// 将等于字元Z
s := string(i)
如何擷取int字元串？
i := 90
// 需要導入“strconv”
s := strconv.Itoa(i)
fmt.Println(s) // Outputs: 90
Golang 字元串
字元串函數
package main
import (
"fmt"
s "strings"
)
func main() {
/* 需要将字元串導入為 s */
fmt.Println(s.Contains("test", "e"))
/* 内置 */
fmt.Println(len("hello")) // => 5
// 輸出: 101
fmt.Println("hello"[1])
// 輸出: e
fmt.Println(string("hello"[1]))
}
fmt.Printf
package main
import (
"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")
}
另見：fmt
函數執行個體
| 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 |
Golang 條件控制
有條件的
a := 10
if a > 20 {
fmt.Println(">")
} else if a < 20 {
fmt.Println("<")
} else {
fmt.Println("=")
}
if 中的語句
x := "hello go!"
if count := len(x); count > 0 {
fmt.Println("Yes")
}
if _, err := doThing(); err != nil {
fmt.Println("Uh oh")
}
Switch
x := 42.0
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")
}
參見：Switch
For loop
for i := 0; i <= 10; i++ {
fmt.Println("i: ", i)
}
對于 Range 循環
nums := []int{2, 3, 4}
sum := 0
for _, num := range nums {
sum += num
}
fmt.Println("sum:", sum)
While 循環
i := 1
for i <= 3 {
fmt.Println(i)
i++
}
Continue 關鍵字
for i := 0; i <= 5; i++ {
if i % 2 == 0 {
continue
}
fmt.Println(i)
}
Break 關鍵字
for {
fmt.Println("loop")
break
}
Golang 結構和映射
定義
package main
import (
"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
}
參見：結構(Structs)
字面量
v := Vertex{X: 1, Y: 2}
// Field names can be omitted
v := Vertex{1, 2}
// Y is implicit
v := Vertex{X: 1}
您還可以輸入字段名
映射
m := make(map[string]int)
m["k1"] = 7
m["k2"] = 13
fmt.Println(m) // => map[k1:7 k2:13]
v1 := m["k1"]
fmt.Println(v1) // => 7
fmt.Println(len(m)) // => 2
delete(m, "k2")
fmt.Println(m) // => map[k1:7]
_, prs := m["k2"]
fmt.Println(prs) // => false
n := map[string]int{"foo": 1, "bar": 2}
fmt.Println(n) // => map[bar:2 foo:1]
指向結構的指針
v := &Vertex{1, 2}
v.X = 2
Doing v.X is the same as doing (*v).X, when v is a pointer.
Golang 函數
多個參數
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))
多次傳回
func vals() (int, int) {
return 3, 7
}
a, b := vals()
fmt.Println(a) // => 3
fmt.Println(b) // => 7
匿名函數
r1, r2 := func() (string, string) {
x := []string{"hello", "world"}
return x[0], x[1]
}()
// => hello world
fmt.Println(r1, r2)
命名傳回
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
變量函數
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
初始化函數
import --> const --> var --> init()
var num = setNumber()
func setNumber() int {
return 42
}
func init() {
num = 0
}
func main() {
fmt.Println(num) // => 0
}
作為值的函數
func main() {
// 将函數賦給名稱
add := func(a, b int) int {
return a + b
}
// 使用名稱調用函數
fmt.Println(add(3, 4)) // => 7
}
關閉 1
func scope() func() int{
outer_var := 2
foo := func() int {return outer_var}
return foo
}
// Outpus: 2
fmt.Println(scope()())
關閉 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()) // => 200
fmt.Println(val) // => 101
Golang 包(Packages)
導入
import "fmt"
import "math/rand"
等同于
import (
"fmt" // 給 fmt.Println
"math/rand" // 給 rand.Intn
)
另見：導入
别名
import r "math/rand"
import (
"fmt"
r "math/rand"
)
r.Intn()
Packages
package main
// 一個内部包隻能被另一個包導入
// 那是在以内部目錄的父級為根的樹内
package internal
另見：内部包
導出名稱
// 以大寫字母開頭
func Hello () {
···
}
另見：導出的名稱
Golang 并發
協程
package main
import (
"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")
}
參見：Goroutines, Channels
WaitGroup
package main
import (
"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()
}
參見：WaitGroup
Closing channels
ch <- 1
ch <- 2
ch <- 3
close(ch) // 關閉頻道
// 疊代通道直到關閉
for i := range ch {
···
}
// Closed if `ok == false`
v, ok := <- ch
參見：範圍和關閉
緩沖通道
ch := make(chan int, 2)
ch <- 1
ch <- 2
ch <- 3
// 緻命錯誤：
// 所有 goroutine 都處于休眠狀态 - 死鎖
參見：緩沖通道
Golang 錯誤控制
延遲函數
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 函數使用目前值d，除非我們使用指針在 main 末尾擷取最終值
Defer
func main() {
defer fmt.Println("Done")
fmt.Println("Working...")
}
參見：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()
參見：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
參見：指針接收器
Golang 接口(Interfaces)
基本接口(Interfaces)
type Shape interface {
Area() float64
Perimeter() float64
}
結構(Struct)
type Rectangle struct {
Length, Width float64
}
結構 Rectangle 通過實作其所有方法隐式實作接口 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 中定義的方法在Rectangle中實作
接口執行個體
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())
}
雜項
關鍵字(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
運算符和标點符号
| + | & | += | &= | && | == | != | ( | ) |
| - | | | -= | |= | || | < | <= | [ | ] |
| * | ^ | *= | ^= | <- | > | >= | { | } |
| / | << | /= | <<= | ++ | = | := | , | ; |
| % | >> | %= | >>= | -- | ! | ... | . | : |
| &^ | &^= |
另見
- 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)
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