Re: [boost] [review] Review of Boost.Exception

From: Sebastian Redl (sebastian.redl_at_[hidden])
Date: 2007-09-30 16:20:37

Dean Michael Berris wrote:
> Hi Emil!
>
>   
> Far from it. I'm thinking get_error_info(T const &) should not compile
> if the error_info being requested has not been passed to the
> exception. This would only be possible if the exception type itself is
> composed using expression templates and its type information is
> somehow reflected during runtime -- or it might be impossible given
> that the exception is referred to via an abstract base `boost::error`.
> Maybe an encapsulated tuple that "grows" along the exception
> propagation might work though I'm not entirely sure about that as
> well.
>   
This is completely impossible. Full static type information would have
to be available in order to compose a new data item into an existing
exception, which means that a site which just wants to add information
would have to catch the exception by its _full expression template
type_. Given that a site might not even _know_ what exceptions might
pass through it (if it's passed a Boost.Function object and calls it,
for example), that's not even possible, not to mention that it would be
completely unusuable if it _were_ possible.

Sebastian Redl