2.22. Go language select statement

发布时间 ： 2025-10-25 13:32:55 UTC      

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

select randomly execute a runnable case . If not, case runnable, it will block until there is case can be run. A default clause should always run.

2.22.1. Grammar #

The syntax of the select statement in the Go programming language is as follows:

select {
    case communication clause  :
       statement(s);
    case communication clause  :
       statement(s);
    /* You can define any number of cases */
    default : /* optional */
       statement(s);
}

The following description describes select syntax of the statement:

  • Each case must be a communication.

  • All channel expressions are evaluated.

  • All expressions sent will be evaluated

  • If any communication can be performed, it is executed and the others are ignored.

  • If there are more than one case can be run. Select will be randomly and fairly selected for execution. The rest will not be carried out. Otherwise:

    1. If there is default clause, the statement is executed.

    2. If there is no default clause, select will block until a communication can run; Go will not re evaluate channel or values.

2.22.2. Example #

select statement application demonstration:

Example # 

package main
import "fmt"
func main() {
   var c1, c2, c3 chan int
   var i1, i2 int
   select {
      case i1 = <- < span>c1:
         fmt.Printf("received ", i1, " from c1\\n")
      case c2 <- < span> i2:
         fmt.Printf("sent ", i2, " to c2\\n")
      case i3, ok := (<- < span>c3):  // same as: i3, ok := <- < span>c3
         if ok {
            fmt.Printf("received ", i3, " from c3\\n")
         } else {
            fmt.Printf("c3 is closed\\n")
         }
      default:
         fmt.Printf("no communication\\n")
   }
}
   
 The result of the above code execution is: 
 
 
 
no communication

 
 
    
                    
                
                

                    

                        

                            
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                            2.22. Go language select statement 
                        

                    

                

            
        
        

            

    
        

            

                

                    
                        
                        
                            
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