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From: brianjparker_at_[hidden]
Date: 2001-10-28 07:50:49

--- In boost_at_y..., Douglas Gregor <gregod_at_c...> wrote:
> I won't claim that the version I supplied definitely covers all
> cases. I would suggest that we follow the approach described at:

I just had a look at this paper- the procedure he describes is, I
think, in essence exactly the same as is used in the alignment_traits
class I submitted (which BTW is based on a class by Valentin
Bonnard). Given a collection of base types that cover all alignment
possibilities, he creates a structure including only the base types
that are smaller than the supplied type.

(Actually, one could add an additional test- that the base type also
has the same alignment as the supplied type- which could in theory
give a less conservative final alignment but could fail if
alignment_of is not accurate.)
> > > Do you agree that boost::alignment_of<T>::align_t would be the
> > > way to integrate it into Boost?
> >
> > Partially.
> > If alignment_of<> didn't existed, and we were creating it, yes,
I think
> > I'll put 'align_t' there.
> > But, given that alignment_of<> is already in use, I'm not sure.
> > We need to know what other boosters think about this.
> I think I like the idea. I only worry about portability because it
requires a
> bit of metaprogramming to get the align_t type, and that would
break under
> some compilers that otherwise work with alignment_of<>.

Yes, I too think we should avoid complicated metaprogramming
implementations to solve this simple problem, both for portability
and to avoid increase compile times. The implementation described in
alexandrescu.pdf seems to require typelists and other metaprogramming
machinery. The implementation I submitted is fairly simple but
requires partial specialisation; perhaps a simpler implementation
could be devised.

> However, we could perhaps use a pessimistic align_t where
> isn't possible to get around this (foolish) problem.

Agreed, in a worst-case scenario align_t could just be a typedef for
some worst-alignment type.

,Brian Parker.

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