[boost] Exception lib proposal update: what()

From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2006-08-21 13:07:13

Hello,

I just finished an update to the exception library I am planning to propose 
for addition to Boost. I appreciate all feedback, including incompatibility 
reports with various compilers (I believe the implementation to be 
standard-conforming, but I have only tested with msvc 7.1/8.0 and gcc 
3.4.4).

As usual, the latest documentation is here:

http://www.revergestudios.com/boost-exception/boost-exception.htm

Here is a zip file with the source code, complete with jamfiles and tests:

http://www.revergestudios.com/boost-exception/boost-exception.zip

Here's what's new in this update: class boost::exception now defines what() 
function, similarly to std::exception. It automatically formats a message 
which combines all exception info stored by operator<< in the 
boost::exception object. The message is not user-friendly; it is designed 
for dumping in log files and for other debugging systems.

For what() to work, the system needs to be able to convert the exception 
info values stored in a boost::exception to string. Because this is not a 
critical feature, I thought it wouldn't be a good idea to require the user 
code to provide such a conversion for everything. The current implementation 
generates a string representation of each exception info value (at the time 
exception_info is called) as follows:

- If a suitable overload for the unqualified call to to_string (passing the 
exception info value as the only argument) is found, that overload is used.

- Otherwise, if a suitable overload for serializing the exception info value 
into a std::ostringstream is found, that overload is used.

- Otherwise the system gives up and uses a generic "stub" string to indicate 
that the exception info value could not be converted to string.

This is accomplished through the to_string function template, which has the 
following signature:

template <class T>
std::string to_string( T const &, char const * stub );

Do you think that to_string is universally useful? Is there anything in 
Boost with similar functionality? Perhaps we can make to_string a separate 
addition to Boost?

Thanks,
Emil