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From: Peter Dimov (pdimov_at_[hidden])
Date: 2008-08-20 12:46:38

Robert Ramey:

> What is an "implicit requirement"? You mean that previous users
> of boost/throw_exception where remiss if they didn't derive
> from std::exception

Yes, they were. This was often caused by silent bugs - throwing enums
instead of the appropriate exception type, in one case.

> or if they didn't surround throw_exception
> with #if BOOST_NO_TYPEID.

No, throw_exception is not supposed to be surrounded by #if BOOST_NO_TYPEID,
and it would in any case be incorrect to do so.

What it _is_ supposed to do is work and not cause problems for people
unaware of Boost.Exception, and it will hopefully be fixed accordingly.

For this to happen, Boost.Config needs to acquire a BOOST_NO_RTTI macro.
Incidentally, g++ 4.3 now seems to have a predefined __GXX_RTTI macro that
we can use to autodetect that BOOST_NO_TYPEID and BOOST_NO_RTTI need to be
set (earlier g++ versions did not).

> Hmmm - It looks to me that the previous code would work fine
> on a no-exeptions platform - all it did was call a user defined
> throw_exception function.

No, it would fail to compile. The user-defined function took an
std::exception argument.

A fundamental issue is that there are many configurations relevant to our
users that we don't test. -Wshadow -Wundef is one, no-exceptions is another,
no-RTTI is a third one. Speaking as a lib maintainer, I try to keep the
libraries working under these conditions, but without test results, it's not
easy to do so.

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