[boost] Re: Advice on using iterator_adaptor

From: Keith MacDonald (boost_at_[hidden])
Date: 2003-09-28 15:00:30

Hi Thomas,

First off, apologies for posting this on the developer mailing list.  I was
trying to use gmane.comp.lib.boost.user, so I don't know how that happened.

My real task is to iterate through a memory mapped file.  The constraint on
Win32 is that MapViewOfFile is limited to a window no larger than the
maximum contiguous area of virtual memory.  Therefore, the iterator will be
more complicated than a simple char*, but I decided to start with that, to
find out how iterator_adaptor worked.

You said "First rule of iterators: Don't derive from an iterator", and I'm
certainly looking for advice, but P.J. Plauger's library always derives
iterator from const_iterator, which is itself derived from a base class.  If
someone can spell out exactly how iterator_adaptor should be used for
creating iterators in new container classes, I'm sure I'll not be the only
one to benefit.

Thanks,
Keith MacDonald

"Thomas Witt" <witt_at_[hidden]> wrote in message
news:3F771ED5.6090205_at_acm.org...
> Thomas Witt wrote:
>
> >
> > Hi Keith,
> >
> > Just a short remark, more to follow.
> >
> > Keith MacDonald wrote:
> >
> >>
> >>     class const_iterator
> >>         : public boost_const_iterator
> >
> >
> > This does not work, it never did and it never will. First rule of
> > iterators: Don't derive from an iterator.
>
> Ok, I messed up. This does work. But
>
> class iterator : public const_iterator { ... };
>
> does not.
>
> There is one thing I don't understand, why do you use ia at all.
> unsigned char* can be used as an iterator an AFAICS you do not adapt the
> underlying iterator in any way.
>
> Thomas
>
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