Re: [boost] [gsoc] Pointer Plus Bits Behavior and Interface

Subject: Re: [boost] [gsoc] Pointer Plus Bits Behavior and Interface
From: Joaquin M Lopez Munoz (joaquin_at_[hidden])
Date: 2010-07-15 13:43:03

David Abrahams <dave <at> boostpro.com> writes:

> 
> 
> On Jul 15, 2010, at 1:09 PM, Andrew Sutton wrote:
> 
> >> One could argue that the bits should be evaluated to produce the
> >> Boolean result as easily as evaluating the pointer.  There are two aspects
> >> in pointer_plus_bits and they shouldn't be obscured or conflated.
> >> 
> > 
> > I strongly disagree with using views in the design of this data structure.
> > It's not such a complex concept that you would need to explicitly decouple
> > its concerns via views. You end up designing a pointer+bits that can't be
> > used natively as a pointer or bits.
> 
> I agree with Andrew.

I disagree with Dave and Andrew. There is no natural concept
around "a pointer plus some bits". These are packed together
to save space, which is an aspect completely orthogonal to
whatever purspose the pointer and the bits serve (separately).

To me, pointer_plus_bits should be as similar as possible
to having two members, one a pointer the other the bits, so
that for instance the following

class X
{
  ...
  pointer ptr;
  bool    b;
};

can be rewritten as

class X
{
  ...
  pointer_plus_bits<...> pb;
};

so as to save memory, with as little change from the original
situation as possible (for instance, instead of x.ptr one would
say x.pb.ptr() and so forth). Overelaborating on an
concept+bits concept seems to me to be missing the point.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo