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