Re: [boost] [concept] concept-based overloading (N2081)

Subject: Re: [boost] [concept] concept-based overloading (N2081)
From: David Abrahams (dave_at_[hidden])
Date: 2010-05-27 21:28:41

At Thu, 27 May 2010 20:30:18 -0400,
Lorenzo Caminiti wrote:
> 
> On Thu, May 27, 2010 at 4:59 PM, Jeffrey Lee Hellrung, Jr.
> <jhellrung_at_[hidden]> wrote:
>
> > And now that I've written this, I see this exact example is already
> > elaborated on at the boost website:
> >
> > http://www.boost.org/community/generic_programming.html#tag_dispatching
> 
> Great! The code from the Boost links above is _exactly_ what I was looking for.

Actually that example is missing one crucial detail: inheritance of
tags matching the refinement hierarchy.  The first few lines *should*
read:

  struct input_iterator_tag { };
  struct bidirectional_iterator_tag : input_iterator_tag { };
  struct random_access_iterator_tag : bidirectional_iterator_tag { };

or, if you want to reflect the standard accurately,

  struct input_iterator_tag { };
  struct forward_iterator_tag : input_iterator_tag { };
  struct bidirectional_iterator_tag : forward_iterator_tag { };
  struct random_access_iterator_tag : bidirectional_iterator_tag { };

That detail is what allows us to avoid writing a separate version of
advance_dispatch for forward iterators.

-- 
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