Re: [Boost-users] Strange iterator_traits of iterator_facade

Subject: Re: [Boost-users] Strange iterator_traits of iterator_facade
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2010-02-26 00:09:19

AMDG

Swerts, Benjamin wrote:
> I have a class that is templated on an iterator type. As it only works
> with bidirectional and random access iterators, I thought I would impose
> that as follows:
>
> template<typename T> class A
> {
>   A() { checkIterator(std::iterator_traits<T>::iterator_category()); };
>
>   template<typename Tag> void checkIterator( Tag );
>   void checkIterator( std::bidirectional_iterator_tag ) {};
>   void checkIterator( std::random_access_iterator_tag ) {};
>   void checkIterator( boost::random_access_traversal_tag ) {};
> };
>
> This works when T is a standard iterator but not when it's one of my
> iterator_facade subclasses. For example:
>
> class const_iterator : public iterator_facade<const_iterator, const B,
> boost::random_access_traversal_tag, B>
>
> When using this class with A<const_iterator> I get a linker error
> because the checkIterator function is called with:
>
> boost::detail::iterator_category_with_traversal<struct
> std::input_iterator_tag,struct boost::random_access_traversal_tag> 
>
> I certainly cannot add a specialization of checkIterator with this tag
> to class A.
> Could anyone shed some light on this problem? I'm working with Boost
> 1.39.0 on MSVC2008SP1.
>   

Try just having a single overload:

void checkIterator(std::bidirectional_iterator_tag) {}

In Christ,
Steven Watanabe