Go language select statement

Go language conditional statements

select Go is a control structure in a similar statement for the switch to communicate. Each case must be a communication operation, either sending or receiving.

select a random case execution can run. If there is no case to run, it will be blocked until the case can be run. A default clause should always be running.

grammar

Go programming language select statement syntax is as follows:

select {
    case communication clause  :
       statement(s);      
    case communication clause  :
       statement(s); 
    /* 你可以定义任意数量的 case */
    default : /* 可选 */
       statement(s);
}

The following describes the syntax of the select statement:

• Each case must be a communication
• All channel expression will be evaluated
• All expressions will be sent to be evaluated
• If a communication may be any, it performs; others are ignored.
• If more than one case can run, Select will randomly select a fair execution. Other not be executed.
  otherwise:
  1. If there is default clause, the statement is executed.
  2. If there is no default clause, select the block until a communication may run; Go to channel or not re-evaluated value.

Examples

package main

import "fmt"

func main() {
   var c1, c2, c3 chan int
   var i1, i2 int
   select {
      case i1 = <-c1:
         fmt.Printf("received ", i1, " from c1\n")
      case c2 <- i2:
         fmt.Printf("sent ", i2, " to c2\n")
      case i3, ok := (<-c3):  // same as: i3, ok := <-c3
         if ok {
            fmt.Printf("received ", i3, " from c3\n")
         } else {
            fmt.Printf("c3 is closed\n")
         }
      default:
         fmt.Printf("no communication\n")
   }    
}

The above code is executed as a result of:

no communication

Go language conditional statements