Go - pipelines

• Ex. Make 3 channels and chan together, print in fmt.Println(<-channel)
• There is no way to check is a channel closed
• Close pipeline safely. Check receive result and close channel.
  
• Range loop support this pattern
  
• Purpose of closing a channel is to notify client. Channel will be gc whenever it is unreachable
• Different from normal channel, file channel must be closed by ourselves
• Close a closed channel will panic