Expand description
Saying things without staking the process on being heard.
println! and eprintln! panic when the write fails, which is the right
call for a program whose output is the result and the wrong one for
anything that has to keep running. A process whose output goes to a pipe
nobody reads any more, or that a supervisor started with its streams
closed, hits a broken pipe the next time it says anything; a server dies
there, in the middle of answering somebody. A lost line of log is the
smaller loss.
So diagnostics go out through here: the line is written whenever anything is listening, and dropped when nothing is.