If OP is looking for ideas, there are two intermediate steps between the extremes of "write every line to stdout" and "build up a buffer of the whole output and

If OP is looking for ideas, there are two intermediate steps between the extremes of "write every line to stdout" and "build up a buffer of the whole output and then write it to stdout". 1. `stdout().lock()` and `writeln!()` to that. By default using `print*!()` will write to `stdout()` which takes a process-wide lock each time. (Funnily enough they use .lock() in the "build up a buffer of the whole output" section, just to do one .write_all() call, which is the one time they don't need to use .lock() because Stdout's impl of write_all() will only take the lock once anyway.) 2. Wrap the locked stdout in a `BufWriter` and `writeln!()` to that. It won't flush on every line, but it also won't buffer the entire output, so it's a middle point between speed and memory usage. --- For the final proc macro approach, there is the option to unroll the loop in the generated code, and the option to generate a &'static str literal of the output.