Re: [Boost-users] Boost.Log formal review upcoming

Subject: Re: [Boost-users] Boost.Log formal review upcoming
From: Eric J. Holtman (eric_at_[hidden])
Date: 2010-03-01 11:47:04

Roland Bock wrote:
>
>
> If the respective parts were header only, I wonder if the same could 
> not be done without the MACROS (but with compiler optimization).
>

No.    If you have a line like

log (level) << Some_Expression ();

there's no compiler optimization (well, probably no optimization)
that can prevent Some_Expression() from being evaluated.

But the macro expands to something along the lines of

if (log.is_filtered (level)) {} else log.streamer ()

so if the line can get trivially filtered, Some_Expression (in the
else clause) never gets evaluated.

Assuming the filtering is fast enough, this allows you to leave
TRACE level logging in a production build, and only turn
it on when you really want it.