Re: [boost] [smart_ptr] Some questions

From: Daniel Frey (d.frey_at_[hidden])
Date: 2008-04-09 15:47:17

On Wed, 2008-04-09 at 14:18 -0400, Frank Mori Hess wrote:
> On Wednesday 09 April 2008 14:13 pm, Daniel Frey wrote:
> > static_cast<T*>(this) should be legal AFAIK (and doesn't need a vtable)
> 
> It works in some cases, but it will fail the 
> smart_ptr/test/shared_from_this_test.cpp test for example.

You are right. Which makes the optimization possible only for cases
where enable_shared_from_this<T> is not a virtual base class of T. What
do you (and others) think about branching enable_shared_from_this<T>
into two classes:

  low_overhead_enable_shared_from_this<T>

and

  feature_rich_enable_shared_from_this<T>

Yes, the names are crap, we need better ones :) Apart from that, I think
it might be worth it. The first one would be the classic one plus the
limitation you pointed out for virtual base classes, with an overhead of
just 4 bytes, while the second one is the trunk version which offers a
lot more features but currently has an overhead of 4 pointers, a vtable
and a bool.

Note that I don't think that one of the classes is "better" than the
other, I just think that each class has valid use cases which can not be
satisfied by the other class.

Regards, Daniel