records that no more values will be sent on the channel.
It is an error if <code>ch</code> is a receive-only channel.
Sending to or closing a closed channel causes a <a href="#Run_time_panics">run-time panic</a>.
Closing the nil channel also causes a <a href="#Run_time_panics">run-time panic</a>.
After calling <code>close</code>, and after any previously
sent values have been received, receive operations will return