MB wrote:
Hi,
I think non-intrusive customization way needs four specializations; 'X', 'const X', 'volatile X' and 'const volatile X'. At last, twenty specializations are required for five metafunctions. I view that's something like the pitfall of public virtual interfaces.
if that is true, then it is certainly bad.
Only range_result_iterator happens to work around by using remove_cv.
See:
I added followings to <libs/range/doc/example.cpp>:
template< class Range > typename boost::range_result_iterator<Range>::type my_begin(Range& rng) { return boost::begin(rng); }
// then... my_begin(cpair); // error
right, because we instantiate range_const_iterator< const T >, which should never happen.
Why not something like:
template< class T > struct range_result_iterator : mpl::eval_if< is_const<T>, range_const_iterator< typename remove_cv<T>::type >, range_iterator< typename remove_cv<T>::type > > { };
Seems right to me. I the latest release I actually added similar stuff to begin(),end() to remove const qualifiers from "const T", since it lead to such "const T" being used to instatiate metafunctions *even though* the overload was never picked. So this means that begin()/end() must also remove volatile. Cute :-) Thanks for the feedback -Thorsten