Re: [boost] Exception lib?

From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2006-07-09 02:52:24

Felipe Magno de Almeida wrote:

> I believe that get_exception_info makes a great difference!
> Obligating your users to use dynamic_cast you're making dynamic_cast
> being part of the interface of your library. Which makes no sense,
> dynamic_casts should be an implementation detail. And implementation
> details shouldnt be exposed by the interface.

I agree with you in principle, but I believe this case is an exception to
that principle.

For the exception library to work, the object thrown by throw failed<T>()
must derive from T and from exception_info. If it was some other library,
there are other implementations possible: maybe to make exception_info a
member, or whatever. But because the whole point is to be able to
catch(exception_info &), and to catch(T&), the exception type must derive
from both.

Therefore users know that dynamic_cast will work, with or without
get_exception_info.

People use interfaces to allow for different implementation strategies. But
the only implementation possible for get_exception_info is to use
dynamic_cast!

Therefore, to me anyway, get_exception_info's purpose is to hide the
dynamic_cast so I don't get emails like "why do you have a dynamic_cast as
part of your interface". It's not part of the interface, it's part of C++.
It does exactly what you need when you catch(T&) and want to see if you can
get an exception_info *.

--Emil