[boost] Re: Extensible polymorphic pointer

From: Philippe A. Bouchard (philippeb_at_[hidden])
Date: 2002-08-07 22:35:00

> > > Isn't it true that get_type_id() make assumptions about the binary
> layout
> > > of the class?  That is undefined, let alone non-portable.
> >
> > Is it a compile-time defined token, not a binary dependency.
> > [...]
>
> If I understand correctly, you assume that the type id is stored
sizeof(int)
> bytes before the object.  First, I don't see how this could possibly be
> true,
> and second, I don't see how this could possible be defined.  There are
> very few guarantees about memory layout, and I don't think any of them
> cover your uses.  If I don't understand your code correctly, perhaps you
> can explain it in great detail.

Well this issue is based purely on the fact that an integer is always the
size of a machine word; they will always be aligned with memory.  Integers
are defined this way in the standards.

Philippe A. Bouchard