122 lines
3.1 KiB
Markdown
122 lines
3.1 KiB
Markdown
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### 带label的continue语句
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- 多用于嵌套循环
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- 终止内层循环用，继续执行外层循环
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- 如果使用`goto`语句不管是内层循环还是外层循环都会被终结，代码将会从 outerloop 这个 label 处，开始重新执行嵌套循环语句，这与带 label 的 continue 的跳转语义是完全不同的
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```go
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func main() {
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var sl = [][]int{
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{1, 34, 26, 35, 78},
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{3, 45, 13, 24, 99},
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{101, 13, 38, 7, 127},
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{54, 27, 40, 83, 81},
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}
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outerloop:
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for i := 0; i < len(sl); i++ {
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for j := 0; j < len(sl[i]); j++ {
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if sl[i][j] == 13 {
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fmt.Printf("found 13 at [%d, %d]\n", i, j)
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continue outerloop
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}
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}
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}
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}
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```
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### 带label的break语句
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- 用于嵌套循环，结束外层循环
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```go
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var gold = 38
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func main() {
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var sl = [][]int{
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{1, 34, 26, 35, 78},
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{3, 45, 13, 24, 99},
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{101, 13, 38, 7, 127},
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{54, 27, 40, 83, 81},
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}
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outerloop:
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for i := 0; i < len(sl); i++ {
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for j := 0; j < len(sl[i]); j++ {
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if sl[i][j] == gold {
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fmt.Printf("found gold at [%d, %d]\n", i, j)
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break outerloop
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}
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}
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}
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}
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```
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### for 循环的坑
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- 循环变量重用，i和v变量只会定义一次，后续每次都是重用。为闭包函数增加参数，传参iv
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```go
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func main() {
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var m = []int{1, 2, 3, 4, 5}
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for i, v := range m {
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go func() {
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time.Sleep(time.Second * 3)
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fmt.Println(i, v)
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}()
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}
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time.Sleep(time.Second * 10)
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}
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```
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- 参与 for range 循环的是 range 表达式的副本，参与循环的a是a的副本，但是修改的是原始的a，数组类型循环可以用切片代替
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```go
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func main() {
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var a = [5]int{1, 2, 3, 4, 5}
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var r [5]int
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fmt.Println("original a =", a)
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for i, v := range a {
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if i == 0 {
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a[1] = 12
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a[2] = 13
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}
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r[i] = v
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}
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fmt.Println("after for range loop, r =", r)
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fmt.Println("after for range loop, a =", a)
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}
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// original a = [1 2 3 4 5]
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// after for range loop, r = [1 2 3 4 5]
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// after for range loop, a = [1 12 13 4 5]
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```
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- 遍历 map 中元素的随机性
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### switch case type
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- x 必须是一个interface{} 接口类型
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- switch不用短变量接收，只会有x的动态类型
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- 用短变量接受还可以获得x的value，v 存储的是变量 x 的动态类型对应的值信息
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- Go 中所有类型都实现了 interface{}类型，所以 case 后面可以是任意类型信息
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- 如果在 switch 后面使用了某个特定的接口类型 I，那么 case 后面就只能使用实现了接口类型 I 的类型了，否则 Go 编译器会报错
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```go
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func main() {
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var x interface{} = Book{Name: "11"}
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switch v := x.(type) {
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case nil:
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println("v is nil")
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case int:
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println("the type of v is int, v =", v)
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case string:
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println("the type of v is string, v =", v)
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case bool:
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println("the type of v is bool, v =", v)
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case Book:
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fmt.Println("the type of v is book, v =", v)
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default:
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println("don't support the type")
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}
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}
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```
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