has_iterator, has_const_iterator metafunctions

[Tomas Puverle (tomas dot puverle at morganstanley dot com)]

This function is useful when using enable_if/disable_if for distinguishing between plain types and ranges of types.

Ideally, this would be added as an include to boost/range/metafunctions.hpp.

Code and test case attached. Tested against boost 1.43.0 with MSVC and gcc 4.2.

[tomas.puverle@…]

A patch for boost range with two new metafunctions and a test case.

[Steven Watanabe]

This would be better implemented as

BOOST_MPL_HAS_XXX_TRAIT_DEF(type);
template<class T>
struct has_iterator : has_type<boost::range_iterator<T> > {};
template<class T>
struct has_const_iterator : has_type<boost::range_const_iterator<T> > {};

[Neil Groves]

I have implemented a solution based primarily on stevens suggestion since using BOOST_MPL_HAS_XX_TRAIT_DEF improves compiler support.

I have chosen to implement this using enable_if to select a base class since this works better on many compilers (due to the base class being dependent on the template parameters) than the snippet posted above.