[Box Backup-dev] Logging

[Chris Wilson]

Hi Martin,

> Sounds like a great plan to me. I was going to propose something in that
> direction when converting from printf to streams. Maybe we could do that
> transition in one go.

That would be a good idea, although it might make the design a little more 
complex. Rather than using varargs, how about the Log::Log function 
just takes a stringstream object as a parameter? Then you could write:

 	std::ostringstream msg;
 	msg << "Failed to open file " << filename;
 	Log::Log(Log::ERROR, msg);

Alternatively, we could make a class of log messages that o
has (overloaded) append methods, and a log(priority) method, so you could 
write:

 	Log::Message msg;
 	msg.append("Failed to open file ").append(filename);
 	msg.log(Log::ERROR)

Or even:

 	Log::Message(Log::ERROR, "Failed to open file ", filename);

where the overloaded constructors (different numbers of string arguments) 
call Log::Log(this) automatically? What do people prefer? I guess Ben 
might like the latter as it avoids the use of overloaded operator<<.

> log4cxx is a good place to look if you need any further inspiration on
> how to do this. It does (almost?) everything you list and much more. I
> doubt Ben would want to use it directly because it would introduce more
> dependencies (it itself is dependent on boost).

I based this idea on Log4j, which I guess is similar to log4cxx, but also 
assuming that Ben wouldn't want to include the whole of log4cxx, or to 
bloat the logging framework more than necessary.

Cheers, Chris.
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