select与switch的区别
No.1 Select:
select只能用于channel的操作,发送或接受数据,如果select有多个分支满足条件,他的特点是->随机选取其中一个满足条件的分支。
官方解释如下:
If multiple cases can proceed, a uniform pseudo-random choice is made to decide which single communication will execute.
下面是Concrete Example:
package mainimport (
"fmt"
"time"
)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 * 1)
c2 <- "two"
}()select {
case msg1 := <-c1:
fmt.Println("msg1 received is:", msg1)
case msg2 := <-c2:
fmt.Println("msg2 received is:", msg2)
}}
虽然代码中select中2个分支的条件都是满足的,但是他不像switch那样按顺序。大家可以吧代码复制了自己测试下。
下面来看看我自己测试个6个结果:
msg1 received is: one
msg2 received is: two
msg2 received is: two
msg1 received is: one
msg2 received is: two
msg1 received is: one
No.2 Switch: 【select与switch的区别】switch分支是按顺序执行的,这点和select不同,可以为各种类型进行分支操作这一点又与select不同,还可以用来判断类型。
下面是Concrete Example:
package mainimport "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")
}
下面的输出结果一目了然我不多解释:
Write 2 as two
It's a weekday
It's after noon
I'm a bool
I'm an int
Don't know type string
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