[boost] Re: typeof: type registration

From: David Abrahams (dave_at_[hidden])
Date: 2004-07-22 12:00:55

"Arkadiy Vertleyb" <vertleyb_at_[hidden]> writes:

> "David Abrahams" <dave_at_[hidden]> wrote
>
>> "Arkadiy Vertleyb" <vertleyb_at_[hidden]> writes:
>> > ultimately, at some point, somebody is writing a CPP file.  This end
> user
>> > has to collect all such headers, and "chain" them in a single header,
> thus
>> > emulating a single enum.
>>
>> That sounds like a serious usability problem to me.  Furthermore,
>> we'll still have an ODR violation if two separately-compiled libraries
>> do the chaining in different ways.  Am I wrong?
>
> Right, but it does provide the ability to create the ODR-complient code
> (even if only inside one module) by
> applying certain discipline...  And I don't quite agree that this discipline
> is too hard to follow.  People use system-wide enums left and
> right...  

Yes, but there's seldom a requirement that they be unique system-wide
while at the same time being distributed across headers.

> and in many cases this is just classes from a couple of libraries
> that the user really needs.
>
> As for separately-compiled libraries, do you think such a library could have
> any remaining traces of the template instantiations we are discussing?

If not, the original ODR problem is a total non-issue from a practical
POV so you might as well go ahead with automatic ID generation.

> Futhermore, without the discipline, provided people don't care about
> ODR, it can be made almost as easy as automatic registration.  For
> example the registration headers can directly #include the
> "enum"-headers, so that if they wern't previously chained, they
> chain in a random way.  Even automatic ID-generation faciities can
> be provided in addition, for end-users who do not care about ODR.

OK.

> But, as it was said here yesturday, I think we should not punish "I
> know what I am doing" group.  Let's at least provide the ability to
> create the ODR-complient code...

If the ODR matters in this case, we have to do it.  Otherwise, I
don't care one way or the other.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com