Re: [boost] [exception][policy]

From: Peter Dimov (pdimov_at_[hidden])
Date: 2008-08-27 16:00:41

David Abrahams:

> So IIUC, your intention was never to require RTTI in throw_exception, ...

The new throw_exception was not supposed to impose any new requirements and 
it certainly was not supposed to break code that worked before. (It almost 
succeeded at that.)

> and Emil didn't know that, so he violated your original intent
> unwittingly.  What about the "weight" of the header and its
> dependencies?  Your usual stance is to avoid such things.

Well, one upside is that exceptions thrown by boost::throw_exception now can 
be used with boost::exception_ptr. This makes exception_ptr more useful and 
requires zero effort from library authors who already throw all their 
exceptions via boost::throw_exception.

The alternative way to provide such functionality would've been through a 
separate throw replacement, part of Boost.Exception. This would indeed have 
had zero impact on the rest of Boost, both in the negative and the positive 
sense. (That is, it would have required every library author willing to 
support exception_ptr to switch from boost::throw_exception to the new 
function.)

It was impossible to predict in advance whether going with option A would be 
worth the trouble. The only way to find out was to try.

I think that (for such a major change) the transition went fairly smoothly. 
We still have the option to revert throw_exception if the "broad discussion" 
that should have happened then but is happening now reaches this conclusion.

Either way, we'll still be ahead of where we were, both because we now have 
BOOST_NO_RTTI and some awareness of its significance, and because the new 
throw_exception caught a few bugs.