reflect.Select() Function in Golang with Examples

Go language provides inbuilt support implementation of run-time reflection and allowing a program to manipulate objects with arbitrary types with the help of reflect package. The reflect.Select() Function in Golang is used to executes a select operation described by the list of cases. To access this function, one needs to imports the reflect package in the program.

Syntax:

func Select(cases []SelectCase) (chosen int, recv Value, recvOK bool)

Parameters: This function takes the following parameters:

• cases : This parameter is the list of cases.

Return Value: This function returns the index of the chosen case.

Below examples illustrate the use of the above method in Golang:

Example 1:

// Golang program to illustrate
// reflect.Select() Function

 package main

 import (
     "fmt"
     "reflect"
 )

func main() {
    c := make(chan int, 1)
    vc := reflect.ValueOf(c)
    succeeded := vc.TrySend(reflect.ValueOf(123))
    fmt.Println(succeeded, vc.Len(), vc.Cap())

    vSend, vZero := reflect.ValueOf(789), reflect.Value{}
    branches := []reflect.SelectCase{
        {Dir: reflect.SelectDefault, Chan: vZero, Send: vZero},
        {Dir: reflect.SelectRecv, Chan: vc, Send: vZero},
        {Dir: reflect.SelectSend, Chan: vc, Send: vSend},
    }

    // use of Select() method
    selIndex, vRecv, sentBeforeClosed := reflect.Select(branches)
    fmt.Println(selIndex)
    fmt.Println(sentBeforeClosed)
    fmt.Println(vRecv.Int())
    vc.Close()
    // Remove the send case branch this time,
    // for it may cause panic.
    selIndex, _, sentBeforeClosed = reflect.Select(branches[:2])
    fmt.Println(selIndex, sentBeforeClosed)
}

Output:

true 1 1
1
true
123
1 false

Example 2:

// Golang program to illustrate
// reflect.Select() Function

 package main

 import (
     "fmt"
     "reflect"
 )

 func main() {
     var sendCh = make(chan int)

     var increaseInt = func(c chan int) {
         for i := 0; i < 8; i++ {
             c <- i
         }
         close(c)
     }

     go increaseInt(sendCh)

     var selectCase = make([]reflect.SelectCase, 1)
     selectCase[0].Dir = reflect.SelectRecv
     selectCase[0].Chan = reflect.ValueOf(sendCh)

     counter := 0
     for counter < 1 {

        // use of Select() method
         chosen, recv, recvOk := reflect.Select(selectCase)
        if recvOk {
             fmt.Println(chosen, recv.Int(), recvOk)

         } else {
             counter++
         }
     }
 }

Output:

0 0 true
0 1 true
0 2 true
0 3 true
0 4 true
0 5 true
0 6 true
0 7 true