Re: [boost] integer_range iterator return by value semantic

From: David Abrahams (abrahams_at_[hidden])
Date: 2000-12-29 13:01:55

----- Original Message -----
From: "Jeremy Siek" <jsiek_at_[hidden]>

>
> I tried changing to return by reference, but ran into really nasty
> VC++ compiler bug.

How bizarre!

> This was the cause of some of the headaches of
> using iterator adaptors in the graph library. I suppose we could
> return by reference as long as the compiler isn't VC++.
>
> As for the concept checking, yes the concept checks would catch
> the reference return type problem, at least on compilers that
> have iterator_traits. Though perhaps there is a way around that...

If you look at boost/detail/iterator.hpp in my proposed binary_search
library you will find boost::detail::iterator_traits<> which will correctly
supply iterator_category and difference_type on all compilers, even for
pointers.

>   template <class TT>
>   struct ForwardIteratorConcept
>   {
>     void constraints() {
>       function_requires< InputIteratorConcept<TT> >();
> #ifndef BOOST_NO_STD_ITERATOR_TRAITS
>       function_requires< ConvertibleConcept<
>         typename std::iterator_traits<TT>::iterator_category,
>         std::forward_iterator_tag> >();
>       typedef typename std::iterator_traits<TT>::reference reference;
>       reference r = *i;
>       ignore_unused_variable_warning(r);
> #endif
>     }
>     TT i;
>   };

Looks good to me.