[boost] Re: Proposal: boost::pool fast pointer

From: Philippe A. Bouchard (philippeb_at_[hidden])
Date: 2002-07-30 16:10:38

> > [...]
> > ptr<Derived> pD = new Derived;
> > ptr<Derived, X> pX = new X;
> > ptr<Derived, Y> pY = new Y;
> >
> > pX = pD; // Won't work
> > pY = pD; // Won't work
> > [...]
>
> Of course, this syntax is clumsier than existing pointers, and also less
> powerful.  For instance, you may have code that knows about X or Y,
> but not about anything derived from X or Y.  Your proposal requires
> such code to know about all possible derivatives in order to work
> properly, which is a fairly restrictive requirement.

Well we could restrict assignments from whom offsets differ only.  Here is a
clumsy compile-time assertion example (I'm sure someone else can build one
more cleanly):

template <void *, void *>
 struct validate_equality;

template <void * _P>
 struct validate_equality<_P, _P>
 {
  static bool const result = true;
 };

Y aY = * reinterpret_cast<Derived *>(0);
Derived aD = * reinterpret_cast<Derived *>(0);

{
 validate_equality<(void *) & aD, (void *) & aD>::result;
}

Philippe A. Bouchard