Re: [boost] [logging] Interest check on logging library.

Subject: Re: [boost] [logging] Interest check on logging library.
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2008-12-27 14:25:20

On Fri, Dec 26, 2008 at 9:48 AM, Jason Wagner <jason_at_[hidden]> wrote:
> Hello all,
>
> I know there are two proposed logging libraries out there for Boost,
> already, but I had a different itch to scratch on a project.  I think I saw
> that Andrey Semashev was going to submit his far more mature version soon,
> but I thought I'd throw my technique out there for an interest check and
> hopefully commentary.  This is very much a prototype-- there's a lot of work
> yet to be done but the basic outline and functionality is implemented.
>
> Getting the code
> ----------------
> http://www.nialscorva.net/boost_logging-0_1.tar.bz2

What is the motivation for using boost::mpl in the logging library? I
didn't look too deeply into your code, but wouldn't something like
this work just as well:

struct logging_debug;
struct logging_release;

template <class>
struct logging_traits;

template <>
logging_traits<logging_debug>
{
  ....
};

In other words, let the user provide an explicit specialization to
configure the logger; once that's done, they just do:

logger<logging_debug> log;

My reasoning is that a logging library should be lightweight in terms
of source code; when I need logging, I'd rather not get boost::mpl
too.

A few more comments:

In general I don't like using macros or #ifdefs, but one place where I
think they are OK is in a logging library interface, partially because
they make it much lighter, and partially because automatically logging
__FILE__, __LINE__, etc. is desirable IMO.

Finally, I think that all the machinery a typical logging lib uses to
kill logging expressions when they're not needed is an overkill. I've
found that using something as simple as the code below works just
fine:

namespace logging
{
  static bool const warnings=false;
  static bool const errors=true;
}

and then:

if( logging::warnings )
  log << "Warning";

where log simply implements std::ostream.

You could put the if in a macro but frankly, I personally don't mind
typing it every time; compared to the rest of the junk I have to type
to format a meaningful logging message, the if is not an issue. As a
bonus, you don't have to worry about functions referenced by a logging
expression being executed when logging is not enabled.

-- 
Emil Dotchevski
Reverge Studios, Inc.
http://www.revergestudios.com/reblog/index.php?n=ReCode