select
只能应用于channel的操作,既可以用于channel的数据接收,也可以用于channel的数据发送。
如果select
的多个分支都满足条件,则会随机的选取其中一个满足条件的分支, 如语言规范中所说:
If multiple cases can proceed, a uniform pseudo-random choice is made to decide which single communication will execute.
`case`语句的表达式可以为一个变量或者两个变量赋值。
有default
语句。
package main import "time" import "fmt" func main() { c1 := make(chan string) c2 := make(chan string) go func() { time.Sleep(time.Second * 1) c1 <- "one" }() go func() { time.Sleep(time.Second * 2) c2 <- "two" }() for i := 0; i < 2; i++ { select { case msg1 := <-c1: fmt.Println("received", msg1) case msg2 := <-c2: fmt.Println("received", msg2) } } }
switch
可以为各种类型进行分支操作, 设置可以为接口类型进行分支判断(通过i.(type))。
switch
分支是顺序执行的,这和select
不同。
package main import "fmt" import "time" func main() { i := 2 fmt.Print("Write ", i, " as ") switch i { case 1: fmt.Println("one") case 2: fmt.Println("two") case 3: fmt.Println("three") } switch time.Now().Weekday() { case time.Saturday, time.Sunday: fmt.Println("It's the weekend") default: fmt.Println("It's a weekday") } t := time.Now() switch { case t.Hour() < 12: fmt.Println("It's before noon") default: fmt.Println("It's after noon") } whatAmI := func(i interface{}) { switch t := i.(type) { case bool: fmt.Println("I'm a bool") case int: fmt.Println("I'm an int") default: fmt.Printf("Don't know type %T\n", t) } } whatAmI(true) whatAmI(1) whatAmI("hey") }