Can someone explain me what this line in iterator.concepts.general#1 means from the C++ standard draft:
For a type
I, letITER_TRAITS(I)denote the typeIifiterator_traits<I>names a specialization generated from the primary template. Otherwise,ITER_TRAITS(I)denotesiterator_traits<I>.
The primary iterator_traits<I> template will fill in members like value_type and reference from corresponding members of I. If your iterator type does not have those members (for example, all pointer types), you can specialize std::iterator_traits<your_iterator_type> to provide those members instead, and provide them in the traits class.
The ITER_TRAITS(I) conceptual metafunction represents this. If there is no specialization of iterator_traits for the iterator type I, then it gets the members from I itself. If it is specialized, then it gets them from iterator_traits<I>.
