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。

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

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")
}