Re: [boost] [gil] Is bit_aligned_pixel_iterator a standard conformant random access iterator?

Subject: Re: [boost] [gil] Is bit_aligned_pixel_iterator a standard conformant random access iterator?
From: Lubomir Bourdev (lbourdev_at_[hidden])
Date: 2010-05-31 15:09:56

On 5/31/10 5:33 AM, "David Abrahams" <dave_at_[hidden]> wrote:
> At Sun, 30 May 2010 16:27:29 -1000,
> Christian Henning wrote:
>> 
>> One of the folks over at MSDN thinks that bit_aligned_pixel_iterator
>> isn't implemented correctly with the interator_facade. He/She also
>> thinks that iterator isn't fully standard compliant since it doesn't
>> give a real reference but a proxy object instead when deferencing. I'm
>> not sure if that's correct. Anyone knows if that's true or not.
> 
> It is indeed correct that ForwardIterator (and thus
> RandomAccessIterator) forbids the use of proxy references.  That
> restriction is supposed to be dropped in C++0x.
> 

That is unfortunate because in many places in GIL we require a proxy
reference - such as dereferencing a planar pixel, for example. I don't see a
way to avoid having proxy references... And we do want GIL iterators to be
random access iterators.

Lubomir