----Original Message---- From: David Abrahams [mailto:dave@boost-consulting.com] Sent: 27 October 2005 12:57 To: boost@lists.boost.org Subject: Re: [boost] alignment trouble with boost::optional
Michael Shepanski <mshepanski@gmail.com> writes:
On 10/26/05, David Abrahams <dave@boost-consulting.com> wrote:
I think the problem is that type_with_alignment can't find a type that has an alignment of 12. Producing an error in that case is the right behavior. We could add the type whose alignment_of<> is 12 to the reperotoire of types being tested by type_with_alignment...
Don't we need to be sure that type_with_alignment<> can accept *any* number that alignment_of<> produces -- or, conversely, make sure that alignment_of<> only produces numbers that type_with_alignment<> can accept? (I'm assuming that we want boost::optional to work all the time, not just for my example.)
Sure, that's what we want. Can you figure out *how*? That's the problem.
In summary: 1. alignment_of<T> produces a number that is a multiple of the required alignment. 2. type_with_alignment<> cannot deal with all the numbers that alignment_of<> produces. Does anyone know of any platform (including platforms that are no longer in use), where the alignment requirement was /not/ a power of two? If not, then alignment_of<> "just" needs to eliminate the factors from its result which are not a power of two. (That would also allow us to eliminate the special case for long double under Borland). -- Martin Bonner Martin.Bonner@Pitechnology.com Pi Technology, Milton Hall, Ely Road, Milton, Cambridge, CB4 6WZ, ENGLAND Tel: +44 (0)1223 441434