Chris@16: // Copyright Daniel Wallin, David Abrahams 2005. Use, modification and
Chris@16: // distribution is subject to the Boost Software License, Version 1.0. (See
Chris@16: // accompanying file LICENSE_1_0.txt or copy at
Chris@16: // http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: #ifndef UNWRAP_CV_REFERENCE_050328_HPP
Chris@16: #define UNWRAP_CV_REFERENCE_050328_HPP
Chris@16: 
Chris@16: #include <boost/parameter/aux_/yesno.hpp>
Chris@16: #include <boost/mpl/bool.hpp>
Chris@16: #include <boost/mpl/identity.hpp>
Chris@16: #include <boost/mpl/eval_if.hpp>
Chris@16: 
Chris@16: namespace boost { template<class T> class reference_wrapper; }
Chris@16: 
Chris@16: namespace boost { namespace parameter { namespace aux {
Chris@16: 
Chris@16: //
Chris@16: // reference_wrapper support -- because of the forwarding problem,
Chris@16: // when passing arguments positionally by non-const reference, we
Chris@16: // ask users of named parameter interfaces to use ref(x) to wrap
Chris@16: // them.
Chris@16: //
Chris@16: 
Chris@16: // is_cv_reference_wrapper returns mpl::true_ if T is of type
Chris@16: // reference_wrapper<U> cv
Chris@16: template <class U>
Chris@16: yes_tag is_cv_reference_wrapper_check(reference_wrapper<U> const volatile*);
Chris@16: no_tag is_cv_reference_wrapper_check(...);
Chris@16: 
Chris@16: template <class T>
Chris@16: struct is_cv_reference_wrapper
Chris@16: {
Chris@16:     BOOST_STATIC_CONSTANT(
Chris@16:         bool, value = (
Chris@16:             sizeof(is_cv_reference_wrapper_check((T*)0)) == sizeof(yes_tag)
Chris@16:         )
Chris@16:     );
Chris@16: 
Chris@16:     typedef mpl::bool_<
Chris@16: #if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
Chris@16:         is_cv_reference_wrapper::
Chris@16: #endif 
Chris@16:     value> type;
Chris@16: };
Chris@16: 
Chris@16: #if BOOST_WORKAROUND(MSVC, == 1200)
Chris@16: template <>
Chris@16: struct is_cv_reference_wrapper<int>
Chris@16:   : mpl::false_ {};
Chris@16: #endif
Chris@16: 
Chris@16: // Needed for unwrap_cv_reference below. T might be const, so
Chris@16: // eval_if might fail because of deriving from T const on EDG.
Chris@16: template <class T>
Chris@16: struct get_type
Chris@16: {
Chris@16:     typedef typename T::type type;
Chris@16: };
Chris@16: 
Chris@16: #if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
Chris@16: template <class T, class is_reference_wrapper = typename is_cv_reference_wrapper<T>::type>
Chris@16: struct unwrap_cv_reference
Chris@16: {
Chris@16:     typedef T type;
Chris@16: };
Chris@16: 
Chris@16: template <class T>
Chris@16: struct unwrap_cv_reference<T const, mpl::false_>
Chris@16: {
Chris@16:     typedef T const type;
Chris@16: };
Chris@16: 
Chris@16: template <class T>
Chris@16: struct unwrap_cv_reference<T, mpl::true_>
Chris@16:   : T
Chris@16: {};
Chris@16: 
Chris@16: #else 
Chris@16: // Produces the unwrapped type to hold a reference to in named<>
Chris@16: // Can't use boost::unwrap_reference<> here because it
Chris@16: // doesn't handle the case where T = reference_wrapper<U> cv
Chris@16: template <class T>
Chris@16: struct unwrap_cv_reference
Chris@16: {
Chris@16:     typedef typename mpl::eval_if<
Chris@16:         is_cv_reference_wrapper<T>
Chris@16:       , get_type<T>
Chris@16:       , mpl::identity<T>
Chris@16:     >::type type;
Chris@16: };
Chris@16: #endif
Chris@16: 
Chris@16: }}} // namespace boost::parameter::aux
Chris@16: 
Chris@16: #endif // UNWRAP_CV_REFERENCE_050328_HPP
Chris@16: