From: Thorsten Ottosen (tottosen_at_[hidden])
Date: 2006-01-06 12:48:33
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