How to use multiple expressions in single case statement? - go

Question

In the below code:
package main
import (
"fmt"
"reflect"
)
type Model1 struct {
ID string
}
type Model2 struct {
ID string
}
func main() {
ch1 := make(chan Model1)
close(ch1)
checkIfChannelClosed(ch1)
ch2 := make(chan Model2)
close(ch2)
checkIfChannelClosed(ch2)
}
func checkIfChannelClosed(ch interface{}) bool {
if reflect.TypeOf(ch).Kind() != reflect.Chan {
fmt.Println("only channels can be closed")
return false
}
ok := true
if ch == nil {
return false
}
switch v := ch.(type) {
case chan Model1:
select {
case _, ok = <-v: // Line 26
default:
}
case chan Model2:
select {
case _, ok = <-v:
default:
}
default:
fmt.Println("Invalid case")
}
if ok {
fmt.Println("channel is open")
} else {
fmt.Println("channel is closed")
}
return ok
}
GoLang compiler does not allow to write multiple expressions in case statement(as shown below). Goal is to avoid redundant code for select:
switch v := ch.(type) {
case chan Model1, chan Model2:
select {
case _, ok = <-v:
default:
}
default:
fmt.Println("Invalid case")
}
How to use multiple expressions with case statement?

Answer 1

I read this in "The Go programming language" chapter 7.13:
In this style, the emphasis is on the concrete types that satisfy the interface, not on the interface’s methods (if indeed it has any),and there is no hiding of information.
So, i think x.(Type) return a concrete type,if you use a multicase in a swith x:=x.(Type), what happend in the follow code?
switch v := ch.(type) {
case chan Model1,int:
//do something
}
just use the reflect.value to do this:
func checkIfChannelClosed(ch interface{}) bool {
v := reflect.ValueOf(ch)
if v.Kind() != reflect.Chan {
fmt.Println("only channels can be closed")
return false
}
_, ok := v.TryRecv()
if ok{
fmt.Println("recv value from channel..")
}else{
fmt.Println("channel is closed or receive cannot finish without blocking")
}
return ok
}