anonymous struct and empty struct
channel, concurrency, go, goroutine
Solution
Composite literals
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.
Problem
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?