For example I have this code:
package main
import (
"fmt"
)
func main() {
c1 := make(chan interface{})
close(c1)
c2 := make(chan interface{})
close(c2)
var c1Count, c2Count int
for i := 1000; i >= 0; i-- {
select {
case <-c1:
c1Count++
case <-c2:
c2Count++
}
}
fmt.Printf("c1Count: %d
c2Count: %d
", c1Count, c2Count)
}
When running, the output will be:
c1Count: 513
c2Count: 488
The thing I don't know is: we create c1 and c2 channel without doing anything. Why in select/case block, c1Count and c2Count can increase value ?
Thanks
The Go Programming Language Specification
After calling close, and after any previously sent values have been received, receive operations will return the zero value for the channel's type without blocking. The multi-valued receive operation returns a received value along with an indication of whether the channel is closed.
You are counting zero values.
For example,
package main
import (
"fmt"
)
func main() {
c1 := make(chan interface{})
close(c1)
c2 := make(chan interface{})
close(c2)
var c1Count, c2Count int
var z1Count, z2Count int
for i := 1000; i >= 0; i-- {
select {
case z1 := <-c1:
c1Count++
if z1 == nil {
z1Count++
}
case z2 := <-c2:
c2Count++
if z2 == nil {
z2Count++
}
}
}
fmt.Printf("c1Count: %d
c2Count: %d
", c1Count, c2Count)
fmt.Printf("z1Count: %d
z2Count: %d
", z1Count, z2Count)
}
Playground: https://play.golang.org/p/tPRkqXrAFno
Output:
c1Count: 511
c2Count: 490
z1Count: 511
z2Count: 490
For statements with range clause
For channels, the iteration values produced are the successive values sent on the channel until the channel is closed. If the channel is nil, the range expression blocks forever.
Close is useful with a for statement with a range clause.