[boost] Re: typeof: type registration

From: David Abrahams (dave_at_[hidden])
Date: 2004-07-22 10:23:23

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

> "David Abrahams" <dave_at_[hidden]> wrote
>
>> "Arkadiy Vertleyb" <vertleyb_at_[hidden]> writes:
>>
>> > - Whenever the user needs to register her own classes, she provides
>> > identifiers by any means she prefers, such as enum, etc., starting from
>> > BOOST_TYPEOF_USER_GROUP.
>>
>> How will multiple independent users, or libraries that use boost,
>> avoid collisions?
>
> If the class is registered in a header, it should be registered against a
> symbol somehow produced from the name of this header (in the similar way to
> include guards).  If the author of such classes wants to be independent, she
> supplies a separate header, where her symbols are enumerated, looking
> somehing like:
>
> enum
> {
>     MY_SYMBOL_1 = BOOST_TYPEOF_LAST,
>     MY_SYMBOL_2,
>     ...
>     MY_SYMBOL_LAST
> };
> #undef BOOST_TYPEOF_LAST
> #define BOOST_TYPEOF_LAST MY_SYMBOL_LAST
>
> 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?

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