Go语言中 select 和 switch 的比较

selectswitch 是 Go语言中进行分支操作的两个方式,各有各的应用场景。

select

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。

default语句。

下面的代码是 go by example 上的例子:

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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

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。

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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")
}