Re: [boost] Boost and exceptions

Subject: Re: [boost] Boost and exceptions
From: Robert Ramey (ramey_at_[hidden])
Date: 2012-06-24 01:40:51

Dave Abrahams wrote:
> on Sat Jun 23 2012, "Robert Ramey" <ramey-AT-rrsd.com> wrote:

> Like some other things we've discussed, that's essentially a C++
> language feature.  You couldn't do a plain "throw e" either, without
> causing the slice.  The only way to propagate the contents of e is
> "throw;", which is obviously incapable of enhancing the thrown
> exception in any way.
>
> The the more you pick at Emil's design and the more I check your
> arguments, the more impressed I am with the care he took.

My reaction is just the opposite

even little things are a problem,  The first thing I looked at was
the documentation of BOOST_THROW_EXCEPTION(e).

If this is invoked at the exception site it works.  If it is invoked
anywhere else - like a rethrow it doesn't.  It's totally non-intuitive
and a trap for users.  There is no mention of this in the documentation.

And of course the whole idea that to gain benefit of a library one
has to change the code of all the other libraries that the application
might use is a big problem for me.  The fact that the author doesn't think
this is a problem is a very strong suggestion to me that I'd find the
library problematic to actually use.

And this is even before I've really even looked at it.  I've more than
a little skeptical.

And I believe that a solution could have been crafted to avoid the issues
that I've raised but that Emil doesn't agree that these concerns are
legimate.  I know steve doesn't agree with me on this either.

So now I would have to provide a counter example which means
basically re-doing the original work in the right way as I see it.

> I may be
> misunderstanding, but IIUC, the "problem" that he "fixed" was that his
> change caused already-unsupported misuses of boost::throw_exception to
> stop compiling.  It's arguable that those misuses *should* be flagged
> with compiler errors.

the original boost::throw_exception was defined as:

#ifdef BOOST_NO_EXCEPTIONS
void throw_exception( std::exception const & e ); // user defined
#else
template<class E>
void throw_exception(E const & e){
    throw(e);
}
#endif

it's hard to see how one could even define "misuse" of this - much
less detect it.

Robert Ramey