http://play.golang.org/p/vhaKi5uVmm
package main
import "fmt"
var battle = make(chan string)
func warrior(name string, done chan struct{}) {
select {
case opponent := <-battle:
fmt.Printf("%s beat %s\n", name, opponent)
case battle <- name:
// I lost :-(
}
done <- struct{}{}
}
func main() {
done := make(chan struct{})
langs := []string{"Go", "C", "C++", "Java", "Perl", "Python"}
for _, l := range langs { go warrior(l, done) }
for _ = range langs { <-done }
}
[1st Question]
done <- struct{}{}
How and Why do we need this weird-looking struct? Is it empty struct or anonymous struct? I googled it but couldn't find the right answer or documentation to explain about this.
The original source is from Andrew Gerrand's talk http://nf.wh3rd.net/10things/#10
Here
make(chan struct{})
done is a channel of type struct{}
So I tried with
done <- struct{}
But it is not working. Why do I need an extra brackets for this line?
done <- struct{}{}
[2nd Question]
for _ = range langs { <-done }
Why do I need this line? I know that this line is necessary because without this line, no output. But Why and what does this line do? And what makes it necessary in this code? I know that <-done is to receive values from the channel done and discard the received values. But why do I need to do this?
Composite literals construct values for structs, arrays, slices, and maps and create a new value each time they are evaluated. They consist of the type of the value followed by a brace-bound list of composite elements. An element may be a single expression or a key-value pair.
struct{}{} is a composite literal of type struct{}, the type of the value followed by a brace-bound list of composite elements.
for _ = range langs { <-done } is waiting until all the goroutines for all the langs have sent done messages.