1406 lines
27 KiB
Markdown
1406 lines
27 KiB
Markdown
Golang 备忘清单
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===
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该备忘单提供了帮助您使用 [Golang](https://golang.org) 的基本语法和方法。
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入门
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--------
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### hello.go
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```go
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package main
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import "fmt"
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func main() {
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fmt.Println("Hello, world!")
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}
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```
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直接运行
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```shell
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$ go run hello.go
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Hello, world!
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```
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或者在 [Go repl](https://repl.it/languages/go) 中尝试一，`go` 命令[参考](#go-命令)
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### 变量
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```go
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var s1 string
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s1 = "Learn Go!"
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// 一次声明多个变量
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var b, c int = 1, 2
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var d = true
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// 匿名赋值
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_ , e = 10, 20
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```
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简短声明
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```go
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s1 := "Learn Go!" // string
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b, c := 1, 2 // int
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d := true // bool
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```
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参见：[基本类型](#golang-基本类型)
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### 函数
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```go
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package main
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import "fmt"
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// 程序的入口点
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func main() {
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fmt.Println("Hello world!")
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say("Hello Go!")
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}
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func say(message string) {
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fmt.Println("You said: ", message)
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}
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```
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参见：[函数(Functions)](#golang-函数)
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### 注释
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```go
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// 单行注释
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/* 这是
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多行注释 */
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```
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### if 语句
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```go
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if true {
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fmt.Println("Yes!")
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}
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```
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参见：[条件控制](#golang-条件控制)
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Golang 基本类型
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--------
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### 字符串 Strings
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```go
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s1 := "Hello" + "World"
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s2 := `A "raw" string literal
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can include line breaks.`
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// 输出：10
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fmt.Println(len(s1))
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// 输出：Hello
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fmt.Println(string(s1[0:5]))
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```
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字符串的类型为 `字符串`
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### 数字 Numbers
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```go
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num := 3 // int
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num := 3. // float64
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num := 3 + 4i // complex128
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num := byte('a') // byte (alias: uint8)
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var u uint = 7 // uint (unsigned)
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var p float32 = 22.7 // 32-bit float
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```
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#### 操作符 Operators
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```go
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x := 5
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x++
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fmt.Println("x + 4 =", x + 4)
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fmt.Println("x * 4 =", x * 4)
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```
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参见：[更多操作符](#运算符和标点符号)
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### 布尔值 Booleans
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```go
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isTrue := true
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isFalse := false
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```
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#### 操作符
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```go
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fmt.Println(true && true) // true
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fmt.Println(true && false) // false
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fmt.Println(true || true) // true
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fmt.Println(true || false) // true
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fmt.Println(!true) // false
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```
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参见：[更多操作符](#运算符和标点符号)
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### 数组 Arrays
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```go
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┌────┬────┬────┬────┬─────┬─────┐
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| 2 | 3 | 5 | 7 | 11 | 13 |
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└────┴────┴────┴────┴─────┴─────┘
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0 1 2 3 4 5
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```
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---
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```go
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primes := [...]int{2, 3, 5, 7, 11, 13}
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fmt.Println(len(primes)) // => 6
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// 输出：[2 3 5 7 11 13]
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fmt.Println(primes)
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// 与 [:3] 相同，输出：[2 3 5]
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fmt.Println(primes[0:3])
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```
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---
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```go
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var a [2]string
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a[0] = "Hello"
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a[1] = "World"
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fmt.Println(a[0], a[1]) //=> Hello World
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fmt.Println(a) // => [Hello World]
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```
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#### 2d array
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```go
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var twoDimension [2][3]int
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for i := 0; i < 2; i++ {
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for j := 0; j < 3; j++ {
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twoDimension[i][j] = i + j
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}
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}
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// => 2d: [[0 1 2] [1 2 3]]
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fmt.Println("2d: ", twoDimension)
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```
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### 指针(Pointers)
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<!--rehype:wrap-class=col-span-2-->
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```go
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func main () {
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b := *getPointer()
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fmt.Println("Value is", b)
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}
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func getPointer () (myPointer *int) {
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a := 234
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return &a
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}
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//申明指针的时候，如果没有指向某个变量，默认值为nil
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//不能直接进行操作，包括读写
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var p *int
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*p = 123 // panic nil pointer
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```
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---
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```go
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//而用new返回的是有默认值的指针, 为数据类型的默认值
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func main(){
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//有一块内存存放了10，它的地址由系统自动分配，别名是a
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a := 10
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//内存存放的10变成了20
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a = 20
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var p *int
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p = &a //或者直接写 p := &a
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//上面的p是一个指针，通过 *p 的方式同样可以访问 变量a指向 的内存
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/*当你动态申请内存的时候，指针的存在意义之一就被体现出来了*/
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ptr := new(int)
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//申请了一块内存空间，没有办法指定别名，new()返回内存地址，用指针接收
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//此时并没有变量能直接指向这块内存，所以只能通过内存地址来访问
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}
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```
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参见：[指针(Pointers)](https://tour.golang.org/moretypes/1)
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### 切片(Slices)
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```go
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s := make([]string, 3)
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s[0] = "a"
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s[1] = "b"
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s = append(s, "d")
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s = append(s, "e", "f")
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fmt.Println(s)
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fmt.Println(s[1])
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fmt.Println(len(s))
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fmt.Println(s[1:3])
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slice := []int{2, 3, 4}
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```
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另见：[切片示例](https://gobyexample.com/slices)
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### 常量(Constants)
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```go
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const s string = "constant"
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const Phi = 1.618
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const n = 500000000
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const d = 3e20 / n
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```
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常量声明可以使用 iota常量生成器 初始化，它用于
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生成一组以相似规则初始化的常量，但是不用每行都
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写一遍初始化表达式。
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注意：
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1. 在一个const声明语句中，在第一个声明的常量所在的行，iota被置为0，然后在每一个有常量声明的行加一。
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2. 写在同一行的值是相同的
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```go
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const (
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a = iota
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b
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c
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)
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// a = 0, b = 1, c = 2
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```
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### 类型转换
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Go语言中不允许隐式转换，所有类型转换必须显式声明（强制转换），而且转换只能发生在两种相互兼容的类型之间。
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```go
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i := 90
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f := float64(i)
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u := uint(i)
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// 将等于字符Z
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s := string(i)
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```
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#### 如何获取int字符串？
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```go
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i := 90
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// 需要导入“strconv”
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s := strconv.Itoa(i)
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fmt.Println(s) // Outputs: 90
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```
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Golang 字符串
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--------
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### 字符串函数
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```go
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package main
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import (
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"fmt"
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s "strings"
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)
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func main() {
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/* 需要将字符串导入为 s */
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fmt.Println(s.Contains("test", "e"))
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/* 内置 */
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fmt.Println(len("hello")) // => 5
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// 输出: 101
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fmt.Println("hello"[1])
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// 输出: e
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fmt.Println(string("hello"[1]))
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}
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```
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### fmt.Printf
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<!--rehype:wrap-class=row-span-2 col-span-2-->
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```go
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package main
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import (
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"fmt"
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"os"
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)
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type point struct {
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x, y int
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}
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func main() {
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p := point{1, 2}
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fmt.Printf("%v\n", p) // => {1 2}
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fmt.Printf("%+v\n", p) // => {x:1 y:2}
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fmt.Printf("%#v\n", p) // => main.point{x:1, y:2}
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fmt.Printf("%T\n", p) // => main.point
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fmt.Printf("%t\n", true) // => TRUE
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fmt.Printf("%d\n", 123) // => 123
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fmt.Printf("%b\n", 14) // => 1110
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fmt.Printf("%c\n", 33) // => !
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fmt.Printf("%x\n", 456) // => 1c8
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fmt.Printf("%f\n", 78.9) // => 78.9
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fmt.Printf("%e\n", 123400000.0) // => 1.23E+08
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fmt.Printf("%E\n", 123400000.0) // => 1.23E+08
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fmt.Printf("%s\n", "\"string\"") // => "string"
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fmt.Printf("%q\n", "\"string\"") // => "\"string\""
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fmt.Printf("%x\n", "hex this") // => 6.86578E+15
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fmt.Printf("%p\n", &p) // => 0xc00002c040
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fmt.Printf("|%6d|%6d|\n", 12, 345) // => | 12| 345|
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fmt.Printf("|%6.2f|%6.2f|\n", 1.2, 3.45) // => | 1.20| 3.45|
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fmt.Printf("|%-6.2f|%-6.2f|\n", 1.2, 3.45) // => |1.20 |3.45 |
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fmt.Printf("|%6s|%6s|\n", "foo", "b") // => | foo| b|
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fmt.Printf("|%-6s|%-6s|\n", "foo", "b") // => |foo |b |
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s := fmt.Sprintf("a %s", "string")
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fmt.Println(s)
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fmt.Fprintf(os.Stderr, "an %s\n", "error")
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}
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```
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另见：[fmt](https://golang.org/pkg/fmt/)
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### 函数实例
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| 实例 | Result |
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| ----------------------------- | ----------- |
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| Contains("test", "es") | true |
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| Count("test", "t") | 2 |
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| HasPrefix("test", "te") | true |
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| HasSuffix("test", "st") | true |
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| Index("test", "e") | 1 |
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| Join([]string{"a", "b"}, "-") | a-b |
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| Repeat("a", 5) | aaaaa |
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| Replace("foo", "o", "0", -1) | f00 |
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| Replace("foo", "o", "0", 1) | f0o |
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| Split("a-b-c-d-e", "-") | [a b c d e] |
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| ToLower("TEST") | test |
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| ToUpper("test") | TEST |
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Golang 条件控制
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--------
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### 有条件的
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```go
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a := 10
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if a > 20 {
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fmt.Println(">")
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} else if a < 20 {
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fmt.Println("<")
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} else {
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fmt.Println("=")
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}
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```
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### if 中的语句
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```go
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x := "hello go!"
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if count := len(x); count > 0 {
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fmt.Println("Yes")
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}
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```
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---
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```go
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if _, err := doThing(); err != nil {
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fmt.Println("Uh oh")
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}
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```
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### Switch
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```go
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x := 42.0
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switch x {
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case 0:
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case 1, 2:
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fmt.Println("Multiple matches")
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case 42: // Don't "fall through".
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fmt.Println("reached")
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case 43:
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fmt.Println("Unreached")
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default:
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fmt.Println("Optional")
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}
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```
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参见：[Switch](https://github.com/golang/go/wiki/Switch)
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### For loop
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```go
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for i := 0; i <= 10; i++ {
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fmt.Println("i: ", i)
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}
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```
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### 对于 Range 循环
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```go
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nums := []int{2, 3, 4}
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sum := 0
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for _, num := range nums {
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sum += num
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}
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fmt.Println("sum:", sum)
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```
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### For 循环
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```go
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i := 1
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for i <= 3 {
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fmt.Println(i)
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i++
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}
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```
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### Continue 关键字
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```go
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for i := 0; i <= 5; i++ {
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if i % 2 == 0 {
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continue
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}
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fmt.Println(i)
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}
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```
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### Break 关键字
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```go
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for {
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fmt.Println("loop")
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break
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}
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```
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Golang 结构和Maps
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--------
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### 定义
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<!--rehype:wrap-class=row-span-2-->
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```go
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package main
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import (
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"fmt"
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)
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type Vertex struct {
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X int
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Y int
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}
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func main() {
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v := Vertex{1, 2}
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v.X = 4
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fmt.Println(v.X, v.Y) // => 4 2
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}
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```
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参见：[结构(Structs)](https://tour.golang.org/moretypes/2)
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### 字面量
|
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```go
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v := Vertex{X: 1, Y: 2}
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// Field names can be omitted
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v := Vertex{1, 2}
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// Y is implicit
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v := Vertex{X: 1}
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```
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您还可以输入字段名
|
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### Maps
|
||
<!--rehype:wrap-class=row-span-2-->
|
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```go
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m := make(map[string]int)
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m["k1"] = 7
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m["k2"] = 13
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fmt.Println(m) // => map[k1:7 k2:13]
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v1 := m["k1"]
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fmt.Println(v1) // => 7
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fmt.Println(len(m)) // => 2
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delete(m, "k2")
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fmt.Println(m) // => map[k1:7]
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_, prs := m["k2"]
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fmt.Println(prs) // => false
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n := map[string]int{"foo": 1, "bar": 2}
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fmt.Println(n) // => map[bar:2 foo:1]
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```
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|
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### 指向结构的指针
|
||
|
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```go
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v := &Vertex{1, 2}
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v.X = 2
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```
|
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|
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Doing `v.X` is the same as doing `(*v).X`, when `v` is a pointer.
|
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|
||
Golang 函数
|
||
--------
|
||
|
||
### 多个参数
|
||
|
||
```go
|
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func plus(a int, b int) int {
|
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return a + b
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}
|
||
func plusPlus(a, b, c int) int {
|
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return a + b + c
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}
|
||
fmt.Println(plus(1, 2))
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fmt.Println(plusPlus(1, 2, 3))
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```
|
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|
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### 多返回值
|
||
|
||
```go
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func vals() (int, int) {
|
||
return 3, 7
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}
|
||
a, b := vals()
|
||
fmt.Println(a) // => 3
|
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fmt.Println(b) // => 7
|
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```
|
||
|
||
### 匿名函数
|
||
|
||
```go
|
||
r1, r2 := func() (string, string) {
|
||
x := []string{"hello", "world"}
|
||
return x[0], x[1]
|
||
}()
|
||
// => hello world
|
||
fmt.Println(r1, r2)
|
||
```
|
||
|
||
### 命名返回值
|
||
|
||
```go
|
||
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
|
||
```
|
||
|
||
### 可变参数函数
|
||
|
||
```go
|
||
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
|
||
// 不定参在内存中是连续存储的
|
||
// 不定参内部再传递的时候，参数也要是不定的
|
||
```
|
||
|
||
### 初始化函数
|
||
|
||
```go
|
||
import --> const --> var --> init()
|
||
```
|
||
|
||
---
|
||
|
||
```go
|
||
var num = setNumber()
|
||
func setNumber() int {
|
||
return 42
|
||
}
|
||
func init() {
|
||
num = 0
|
||
}
|
||
func main() {
|
||
fmt.Println(num) // => 0
|
||
}
|
||
```
|
||
|
||
### 作为值的函数
|
||
|
||
```go
|
||
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
|
||
}
|
||
```
|
||
|
||
### 闭包
|
||
<!--rehype:wrap-class=col-span-2 row-span-2-->
|
||
```go
|
||
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(val)
|
||
// => 101
|
||
fmt.Println(inner())
|
||
// => 200，这里涉及到golang中闭包和内存逃逸的概念，inner()实际上执行了两次，outer()中一次，fmt又一次，
|
||
//但为什么是200呢，编译器不能确定outer_var在后续会不会使用，
|
||
//所以outer_var不会随着outer()结束而释放它的栈（Stack）空间，
|
||
//而会‘逃逸到’堆（Heap）上，那么第二次的inner()中outer_var就会是101。
|
||
```
|
||
|
||
### 关闭 1
|
||
|
||
```go
|
||
func scope() func() int{
|
||
outer_var := 2
|
||
foo := func() int {return outer_var}
|
||
return foo
|
||
}
|
||
// Outpus: 2
|
||
fmt.Println(scope()())
|
||
```
|
||
|
||
Golang 包(Packages)
|
||
--------
|
||
|
||
### 导入
|
||
<!--rehype:wrap-class=row-span-2-->
|
||
|
||
```go
|
||
import "fmt"
|
||
import "math/rand"
|
||
```
|
||
|
||
#### 等同于
|
||
|
||
```go
|
||
import (
|
||
"fmt" // 给 fmt.Println
|
||
"math/rand" // 给 rand.Intn
|
||
)
|
||
```
|
||
|
||
另见：[导入](https://tour.golang.org/basics/1)
|
||
|
||
### 别名
|
||
<!--rehype:wrap-class=row-span-2-->
|
||
|
||
```go
|
||
import r "math/rand"
|
||
```
|
||
|
||
---
|
||
|
||
```go
|
||
import (
|
||
"fmt"
|
||
r "math/rand"
|
||
)
|
||
```
|
||
|
||
---
|
||
|
||
```go
|
||
r.Intn()
|
||
```
|
||
|
||
### Packages
|
||
|
||
```go
|
||
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](https://go.dev/doc/go1.4#internalpackages)
|
||
|
||
### 导出名称
|
||
|
||
```go
|
||
// 以大写字母开头
|
||
func Hello () {
|
||
···
|
||
}
|
||
```
|
||
|
||
另见：[导出的名称](https://tour.golang.org/basics/3)
|
||
|
||
Golang 并发
|
||
--------
|
||
|
||
### 协程
|
||
<!--rehype:wrap-class=row-span-2-->
|
||
|
||
```go
|
||
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")
|
||
}
|
||
```
|
||
|
||
参见：[Goroutines](https://tour.golang.org/concurrency/1), [Channels](https://tour.golang.org/concurrency/2)
|
||
|
||
### WaitGroup
|
||
<!--rehype:wrap-class=row-span-2-->
|
||
|
||
```go
|
||
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()
|
||
}
|
||
```
|
||
|
||
参见：[WaitGroup](https://golang.org/pkg/sync/#WaitGroup)
|
||
|
||
### Closing channels
|
||
|
||
```go
|
||
ch <- 1
|
||
ch <- 2
|
||
ch <- 3
|
||
close(ch) // 关闭频道
|
||
```
|
||
|
||
---
|
||
|
||
```go
|
||
// 迭代通道直到关闭
|
||
for i := range ch {
|
||
···
|
||
}
|
||
```
|
||
|
||
---
|
||
|
||
```go
|
||
// Closed if `ok == false`
|
||
v, ok := <- ch
|
||
```
|
||
|
||
参见：[范围和关闭](https://tour.golang.org/concurrency/4)
|
||
|
||
### 缓冲通道
|
||
|
||
```go
|
||
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](https://tour.golang.org/concurrency/3)
|
||
|
||
Golang 错误控制
|
||
--------
|
||
|
||
### 延迟函数
|
||
|
||
```go
|
||
func main() {
|
||
defer func() {
|
||
fmt.Println("Done")
|
||
}()
|
||
fmt.Println("Working...")
|
||
}
|
||
```
|
||
|
||
### Lambda defer
|
||
|
||
```go
|
||
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
|
||
|
||
```go
|
||
func main() {
|
||
defer fmt.Println("Done")
|
||
fmt.Println("Working...")
|
||
}
|
||
```
|
||
|
||
参见：[Defer, panic and recover](https://blog.golang.org/defer-panic-and-recover)
|
||
|
||
Golang 方法(Methods)
|
||
--------
|
||
<!--rehype:body-class=cols-2-->
|
||
|
||
### 接收器
|
||
<!--rehype:wrap-class=row-span-2-->
|
||
```go
|
||
//Go语言中的方法（Method）是一种作用于特定类型变量的函数。
|
||
//这种特定类型变量叫做接收者（Receiver）。
|
||
//接收者的概念就类似于其他语言中的 this 或者 self。
|
||
//方法的定义格式如下：
|
||
func (接收者变量 接收者类型) 方法名(参数列表) (返回参数) {
|
||
函数体
|
||
}
|
||
// 其中，
|
||
// 1.接收者变量：接收者中的参数变量名在命名时，官方建议使用接收者类型名
|
||
//的第一个小写字母，而不是self、this之类的命名。例如，Person类型的接收者变量
|
||
// 应该命名为 p，Connector类型的接收者变量应该命名为c等。
|
||
// 2.接收者类型：接收者类型和参数类似，可以是指针类型和非指针类型。
|
||
// 3.方法名、参数列表、返回参数：具体格式与函数定义相同。
|
||
type Vertex struct {
|
||
X, Y float64
|
||
}
|
||
|
||
func (v Vertex) Abs() float64 {
|
||
return math.Sqrt(v.X * v.X + v.Y * v.Y)
|
||
}
|
||
func (v Vertex) valuechange() float64 {
|
||
v.X += 1
|
||
return v.X
|
||
}
|
||
func (v *Vertex) pointerchange() float64 {
|
||
v.X += 1
|
||
return v.X
|
||
}
|
||
func main() {
|
||
v := Vertex{1, 2}
|
||
v.Abs()
|
||
|
||
v = Vertex{1, 2}
|
||
fmt.Println(v.valuechange()) // 2
|
||
fmt.Println(v) // {1 2}
|
||
|
||
v = Vertex{1, 2}
|
||
fmt.Println(v.pointerchange())// 2
|
||
fmt.Println(v) // {2 2}
|
||
}
|
||
//如果在方法里修改receiver的值要对caller生效，使用 pointer receiver。
|
||
|
||
```
|
||
|
||
参见：[Methods](https://tour.golang.org/methods/1)，[指针接收器](https://tour.golang.org/methods/4)
|
||
|
||
### 方法表达式
|
||
|
||
方法表达式相当于提供一种语法将类型方法调用显式地转换为函数调用，接收者(receiver)必须显式地传递进去。
|
||
|
||
```go
|
||
func (t T) Get(){
|
||
return t.a
|
||
}
|
||
func (t *T) Set(i int){
|
||
t.a = i
|
||
}
|
||
//表达式`T.Get`和`(*T).Set`被称为方法表达式，
|
||
//需要注意的是在方法表达式中编译器不会做自动转换。
|
||
//值调用会自动转换，表达式调用则不会，例如：
|
||
type Data struct{}
|
||
func (Data) TestValue () {}
|
||
func (*Data) TestPointer () {}
|
||
//声明一个类型变量a
|
||
var a Data= struct{}{}
|
||
//表达式调用编译器不会进行自动转换
|
||
Data.TestValue(a)
|
||
//Data.TestValue(&a)
|
||
(*Data).TestPointer (&a)
|
||
//Data.TestPointer(&a) //type Data has no method TestPointer
|
||
//值调用编译器会进行自动转换
|
||
y : = (&a).TestValue //编译器帮助转换a.TestValue
|
||
g : = a.TestPointer //会转换为(&a).TestPointer
|
||
```
|
||
|
||
#### 组合结构的方法集
|
||
|
||
内嵌字段的访问不需要使用全路径，只要保证命名是唯一的就可以，尽量避免同名。如果外层字段和内层字段有相同的方法，则使用简化模式访问外层方法会覆盖内层的方法。
|
||
|
||
```go
|
||
x : = X{a: 1}
|
||
y : = Y{
|
||
X : x ,
|
||
b : 2 ,
|
||
}
|
||
z : = z {
|
||
Y : y ,
|
||
c : 3 ,
|
||
}//组合结构，内嵌字段
|
||
```
|
||
|
||
组合结构的方法集有如下规则：
|
||
|
||
- 若类型 T 包含匿名字段 S ，则 T 的方法集包含S的方法集
|
||
- 若类型 T 包含匿名字段 *S ，则 T 的方法集包含 S 和*S方法集
|
||
- 不管类型 T 中嵌入的匿名字段是 S 还是 *S ，*T 方法集总是包含 S 和 *S 方法集
|
||
|
||
Golang 接口(Interfaces)
|
||
--------
|
||
<!--rehype:body-class=cols-2-->
|
||
|
||
### 基本接口(Interfaces)
|
||
|
||
```go
|
||
type Shape interface {
|
||
Area() float64
|
||
Perimeter() float64
|
||
}
|
||
```
|
||
|
||
### 结构(Struct)
|
||
|
||
```go
|
||
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)
|
||
|
||
```go
|
||
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
|
||
|
||
```go
|
||
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())
|
||
}
|
||
```
|
||
<!--rehype:className=wrap-text -->
|
||
|
||
Golang Embed (Go version >= 1.16)
|
||
---
|
||
|
||
### 嵌入为string
|
||
|
||
``` go
|
||
package main
|
||
|
||
import (
|
||
_ "embed"
|
||
"fmt"
|
||
)
|
||
|
||
//go:embed version.txt
|
||
var version string
|
||
|
||
func main() {
|
||
fmt.Printf("version %q\n", version)
|
||
}
|
||
```
|
||
|
||
### 嵌入为[]byte
|
||
|
||
``` go
|
||
package main
|
||
import (
|
||
_ "embed"
|
||
"fmt"
|
||
)
|
||
|
||
//go:embed version.txt
|
||
var versionByte []byte
|
||
|
||
func main() {
|
||
fmt.Printf("version %q\n", string(versionByte))
|
||
}
|
||
```
|
||
|
||
### 嵌入为embed.FS
|
||
|
||
``` go
|
||
//go:embed hello.txt
|
||
var f embed.FS
|
||
func main() {
|
||
data, _ := f.ReadFile("hello.txt")
|
||
fmt.Println(string(data))
|
||
}
|
||
```
|
||
|
||
### 嵌入多个文件
|
||
|
||
``` go
|
||
//go:embed hello.txt
|
||
//go:embed hello2.txt
|
||
var f embed.FS
|
||
func main() {
|
||
data, _ := f.ReadFile("hello.txt")
|
||
fmt.Println(string(data))
|
||
data, _ = f.ReadFile("hello2.txt")
|
||
fmt.Println(string(data))
|
||
}
|
||
```
|
||
|
||
### 嵌入子文件夹下的文件
|
||
|
||
``` go
|
||
//go:embed p/hello.txt p/hello2.txt
|
||
var f embed.FS
|
||
func main() {
|
||
data, _ := f.ReadFile("p/hello.txt")
|
||
fmt.Println(string(data))
|
||
data, _ = f.ReadFile("p/hello2.txt")
|
||
fmt.Println(string(data))
|
||
}
|
||
```
|
||
|
||
### 同一个文件嵌入为多个变量
|
||
|
||
``` go
|
||
//go:embed hello.txt
|
||
var s string
|
||
//go:embed hello.txt
|
||
var s2 string
|
||
func main() {
|
||
fmt.Println(s)
|
||
fmt.Println(s2)
|
||
}
|
||
```
|
||
|
||
### 匹配模式
|
||
|
||
``` go
|
||
//go:embed p/*
|
||
var f embed.FS
|
||
func main() {
|
||
data, _ := f.ReadFile("p/.hello.txt")
|
||
fmt.Println(string(data))
|
||
data, _ = f.ReadFile("p/q/.hi.txt") // 没有嵌入 p/q/.hi.txt
|
||
fmt.Println(string(data))
|
||
}
|
||
```
|
||
|
||
Golang 泛型 (Go version >= 1.18)
|
||
-------------
|
||
|
||
### 泛型类型
|
||
<!--rehype:wrap-class=row-span-1-->
|
||
|
||
```text
|
||
type S[T int|float32|float64 ] []T
|
||
┬ ────────┬────────
|
||
┆ ╰─── 2. 类型约束
|
||
╰────────────── 1. 类型形参
|
||
```
|
||
<!--rehype:className=wrap-text -->
|
||
|
||
可以使用类型实参 int 或 string 实例化
|
||
|
||
``` go
|
||
type MyMap[K int|string, V float32 | float64] map[K]V
|
||
|
||
var a MyMap[string, float64] = map[string]float64{
|
||
"jack_score": 9.6,
|
||
"bob_score": 8.4,
|
||
}
|
||
```
|
||
<!--rehype:className=wrap-text -->
|
||
- **匿名结构体不支持泛型**<!--rehype:style=color: #b43c29;-->
|
||
- **匿名函数不支持泛型**<!--rehype:style=color: #b43c29;-->
|
||
|
||
### 泛型函数
|
||
<!--rehype:wrap-class=row-span-1-->
|
||
|
||
任意类型
|
||
|
||
``` go
|
||
func Add[T any](a,b T) T {
|
||
return a+b
|
||
}
|
||
```
|
||
|
||
对类型进行约束
|
||
|
||
``` go
|
||
func Add[T string | int | int8](a,b T) T {
|
||
return a+b
|
||
}
|
||
```
|
||
|
||
类型嵌套
|
||
|
||
``` go
|
||
type WowStruct[T int | float32, S []T] struct {
|
||
Data S
|
||
MaxValue T
|
||
MinValue T
|
||
}
|
||
|
||
var ws WowStruct[int, []int]
|
||
```
|
||
<!--rehype:className=wrap-text -->
|
||
|
||
泛型函数中进行类型声明 (go version >= 1.20)
|
||
|
||
``` go
|
||
func F[T1 any]() {
|
||
type x struct{}
|
||
type y = x
|
||
}
|
||
```
|
||
|
||
### 泛型约束
|
||
<!--rehype:wrap-class=row-span-2-->
|
||
|
||
通过接口实现
|
||
|
||
``` go
|
||
type Addable interface{
|
||
type int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, uintptr, float32, float64, complex64, complex128, string
|
||
}
|
||
|
||
func Add[T Addable](a,b T) T {
|
||
return a+b
|
||
}
|
||
```
|
||
<!--rehype:className=wrap-text -->
|
||
|
||
使用 ~ 符号
|
||
|
||
``` go
|
||
type Int interface {
|
||
~int | ~int8 | ~int16 | ~int32 | ~int64
|
||
}
|
||
|
||
type Uint interface {
|
||
~uint | ~uint8 | ~uint16 | ~uint32
|
||
}
|
||
type Float interface {
|
||
~float32 | ~float64
|
||
}
|
||
|
||
type Slice[T Int | Uint | Float] []T
|
||
|
||
var s Slice[int] // 正确
|
||
|
||
type MyInt int
|
||
var s2 Slice[MyInt] // MyInt底层类型是int，所以可以用于实例化
|
||
|
||
type MyMyInt MyInt
|
||
var s3 Slice[MyMyInt] // 正确。MyMyInt 虽然基于 MyInt ，但底层类型也是int，所以也能用于实例化
|
||
|
||
type MyFloat32 float32 // 正确
|
||
var s4 Slice[MyFloat32]
|
||
```
|
||
<!--rehype:className=wrap-text -->
|
||
|
||
使用 ~ 时的限制：
|
||
<!--rehype:style=color: #b43c29;-->
|
||
1. ~后面的类型不能为接口
|
||
2. ~后面的类型必须为基本类型
|
||
<!--rehype:style=color: #b43c29;-->
|
||
|
||
### 泛型 Receiver
|
||
<!--rehype:wrap-class=row-span-1-->
|
||
|
||
定义普通类型支持泛型
|
||
|
||
``` go
|
||
type MySlice[T int | float32] []T
|
||
|
||
func (s MySlice[T]) Sum() T {
|
||
var sum T
|
||
for _, value := range s {
|
||
sum += value
|
||
}
|
||
return sum
|
||
}
|
||
```
|
||
<!--rehype:className=wrap-text -->
|
||
|
||
结构体支持泛型
|
||
|
||
``` go
|
||
type A[T int | float32 | float64] struct {
|
||
}
|
||
|
||
func (receiver A[T]) Add(a T, b T) T {
|
||
return a + b
|
||
}
|
||
|
||
```
|
||
<!--rehype:className=wrap-text -->
|
||
|
||
### 泛型接口
|
||
<!--rehype:wrap-class=row-span-1-->
|
||
|
||
``` go
|
||
type Uint interface { // 接口 Uint 中有类型，所以是一般接口
|
||
~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64
|
||
}
|
||
|
||
type ReadWriter interface { // ReadWriter 接口既有方法也有类型，所以是一般接口
|
||
~string | ~[]rune
|
||
|
||
Read(p []byte) (n int, err error)
|
||
Write(p []byte) (n int, err error)
|
||
}
|
||
```
|
||
<!--rehype:className=wrap-text -->
|
||
|
||
一般接口类型不能用来定义变量，只能用于泛型的类型约束中
|
||
<!--rehype:style=color: #b43c29;-->
|
||
|
||
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
|
||
<!--rehype:className=cols-3 style-none-->
|
||
|
||
### 运算符和标点符号
|
||
|
||
| | | | | | | | | |
|
||
| --- | ---- | ----- | ----- | ------ | ---- | ----- | --- | --- |
|
||
| `+` | `&` | `+=` | `&=` | `&&` | `==` | `!=` | `(` | `)` |
|
||
| `-` | `\|` | `-=` | `\|=` | `\|\|` | `<` | `<=` | `[` | `]` |
|
||
| `*` | `^` | `*=` | `^=` | `<-` | `>` | `>=` | `{` | `}` |
|
||
| `/` | `<<` | `/=` | `<<=` | `++` | `=` | `:=` | `,` | `;` |
|
||
| `%` | `>>` | `%=` | `>>=` | `--` | `!` | `...` | `.` | `:` |
|
||
| | `&^` | `&^=` | | | | | | |
|
||
|
||
Go 命令
|
||
---
|
||
|
||
### Go 编译器命令
|
||
|
||
:- | --
|
||
:- | --
|
||
`go command [参数]` | go 命令 [参数]
|
||
`go build` | 编译包和依赖包
|
||
`go clean` | 移除对象和缓存文件
|
||
`go doc` | 显示包的文档
|
||
`go env` | 打印go的环境变量信息
|
||
`go bug` | 报告bug
|
||
`go fix` | 更新包使用新的api
|
||
`go fmt` | 格式规范化代码
|
||
`go generate` | 通过处理资源生成go文件
|
||
`go get` | 下载并安装包及其依赖
|
||
`go install` | 编译和安装包及其依赖
|
||
`go list` | 列出所有包
|
||
`go run` | 编译和运行go程序
|
||
`go test` | 测试
|
||
`go tool` | 运行给定的go工具
|
||
`go version` | 显示go当前版本
|
||
`go vet` | 发现代码中可能的错误
|
||
|
||
### ENV
|
||
|
||
:- | --
|
||
:- | --
|
||
`GOOS` | 编译系统
|
||
`GOARCH` | 编译arch
|
||
`GO111MODULE` | gomod开关
|
||
`GOPROXY` | go代理 <https://goproxy.io> <https://goproxy.cn> <https://mirrors.aliyun.com/goproxy/>
|
||
`GOSSAFUNC` | 生成 `SSA.html` 文件，展示代码优化的每一步 `GOSSAFUNC=func_name go build`
|
||
<!--rehype:className=style-list-arrow-->
|
||
|
||
### Module
|
||
|
||
:- | --
|
||
:- | --
|
||
`go mod init` | 初始化当前文件夹，创建go.mod文件
|
||
`go mod download` | 下载依赖的module到本地
|
||
`go mod tidy` | 增加缺少的module，删除无用的module
|
||
`go mod vendor` | 将依赖复制到vendor下
|
||
文件 `go.mod` | 依赖列表和版本约束
|
||
文件 `go.sum` | 记录 `module` 文件 `hash` 值，用于安全校验
|
||
<!--rehype:className=style-list-arrow-->
|
||
|
||
另见
|
||
--------
|
||
|
||
- [Devhints](https://devhints.io/go) *(devhints.io)*
|
||
- [A tour of Go](https://tour.golang.org/welcome/1) *(tour.golang.org)*
|
||
- [Golang wiki](https://github.com/golang/go/wiki/) *(github.com)*
|
||
- [Effective Go](https://golang.org/doc/effective_go.html) *(golang.org)*
|
||
- [Go by Example](https://gobyexample.com/) *(gobyexample.com)*
|
||
- [Awesome Go](https://awesome-go.com/) *(awesome-go.com)*
|
||
- [JustForFunc Youtube](https://www.youtube.com/channel/UC_BzFbxG2za3bp5NRRRXJSw) *(youtube.com)*
|
||
- [Style Guide](https://github.com/golang/go/wiki/CodeReviewComments) *(github.com)*
|