Range and Close

A sender can close a channel to indicate that no more values will be sent. Receivers can test whether a channel has been closed by assigning a second parameter to the receive expression: after 

  1. v, ok := <-ch

ok is false if there are no more values to receive and the channel is closed.

The loop for i := range c receives values from the channel repeatedly until it is closed.

Note: Only the sender should close a channel, never the receiver. Sending on a closed channel will cause a panic.

Another note: Channels aren't like files; you don't usually need to close them. Closing is only necessary when the receiver must be told there are no more values coming, such as to terminate a range loop.

range-and-close.go

  1. package main
  3. import (
  4.     "fmt"
  5. )
  7. func fibonacci(n int, c chan int) {
  8.     x, y := 0, 1
  9.     for i := 0; i < n; i++ {
  10.         c <- x
  11.         x, y = y, x+y
  12.     }
  13.     close(c)
  14. }
  16. func main() {
  17.     c := make(chan int, 10)
  18.     go fibonacci(cap(c), c)
  19.     for i := range c {
  20.         fmt.Println(i)
  21.     }
  22. }