| // Copyright David Abrahams 2003. 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 IS_LVALUE_ITERATOR_DWA2003112_HPP |
| # define IS_LVALUE_ITERATOR_DWA2003112_HPP |
| |
| #include <boost/iterator.hpp> |
| |
| #include <boost/detail/workaround.hpp> |
| #include <boost/detail/iterator.hpp> |
| |
| #include <boost/iterator/detail/any_conversion_eater.hpp> |
| |
| // should be the last #includes |
| #include <boost/type_traits/detail/bool_trait_def.hpp> |
| #include <boost/iterator/detail/config_def.hpp> |
| |
| #ifndef BOOST_NO_IS_CONVERTIBLE |
| |
| namespace boost { |
| |
| namespace detail |
| { |
| #ifndef BOOST_NO_LVALUE_RETURN_DETECTION |
| // Calling lvalue_preserver( <expression>, 0 ) returns a reference |
| // to the expression's result if <expression> is an lvalue, or |
| // not_an_lvalue() otherwise. |
| struct not_an_lvalue {}; |
| |
| template <class T> |
| T& lvalue_preserver(T&, int); |
| |
| template <class U> |
| not_an_lvalue lvalue_preserver(U const&, ...); |
| |
| # define BOOST_LVALUE_PRESERVER(expr) detail::lvalue_preserver(expr,0) |
| |
| #else |
| |
| # define BOOST_LVALUE_PRESERVER(expr) expr |
| |
| #endif |
| |
| // Guts of is_lvalue_iterator. Value is the iterator's value_type |
| // and the result is computed in the nested rebind template. |
| template <class Value> |
| struct is_lvalue_iterator_impl |
| { |
| // Eat implicit conversions so we don't report true for things |
| // convertible to Value const& |
| struct conversion_eater |
| { |
| conversion_eater(Value&); |
| }; |
| |
| static char tester(conversion_eater, int); |
| static char (& tester(any_conversion_eater, ...) )[2]; |
| |
| template <class It> |
| struct rebind |
| { |
| static It& x; |
| |
| BOOST_STATIC_CONSTANT( |
| bool |
| , value = ( |
| sizeof( |
| is_lvalue_iterator_impl<Value>::tester( |
| BOOST_LVALUE_PRESERVER(*x), 0 |
| ) |
| ) == 1 |
| ) |
| ); |
| }; |
| }; |
| |
| #undef BOOST_LVALUE_PRESERVER |
| |
| // |
| // void specializations to handle std input and output iterators |
| // |
| template <> |
| struct is_lvalue_iterator_impl<void> |
| { |
| template <class It> |
| struct rebind : boost::mpl::false_ |
| {}; |
| }; |
| |
| #ifndef BOOST_NO_CV_VOID_SPECIALIZATIONS |
| template <> |
| struct is_lvalue_iterator_impl<const void> |
| { |
| template <class It> |
| struct rebind : boost::mpl::false_ |
| {}; |
| }; |
| |
| template <> |
| struct is_lvalue_iterator_impl<volatile void> |
| { |
| template <class It> |
| struct rebind : boost::mpl::false_ |
| {}; |
| }; |
| |
| template <> |
| struct is_lvalue_iterator_impl<const volatile void> |
| { |
| template <class It> |
| struct rebind : boost::mpl::false_ |
| {}; |
| }; |
| #endif |
| |
| // |
| // This level of dispatching is required for Borland. We might save |
| // an instantiation by removing it for others. |
| // |
| template <class It> |
| struct is_readable_lvalue_iterator_impl |
| : is_lvalue_iterator_impl< |
| BOOST_DEDUCED_TYPENAME boost::detail::iterator_traits<It>::value_type const |
| >::template rebind<It> |
| {}; |
| |
| template <class It> |
| struct is_non_const_lvalue_iterator_impl |
| : is_lvalue_iterator_impl< |
| BOOST_DEDUCED_TYPENAME boost::detail::iterator_traits<It>::value_type |
| >::template rebind<It> |
| {}; |
| } // namespace detail |
| |
| // Define the trait with full mpl lambda capability and various broken |
| // compiler workarounds |
| BOOST_TT_AUX_BOOL_TRAIT_DEF1( |
| is_lvalue_iterator,T,::boost::detail::is_readable_lvalue_iterator_impl<T>::value) |
| |
| BOOST_TT_AUX_BOOL_TRAIT_DEF1( |
| is_non_const_lvalue_iterator,T,::boost::detail::is_non_const_lvalue_iterator_impl<T>::value) |
| |
| } // namespace boost |
| |
| #endif |
| |
| #include <boost/iterator/detail/config_undef.hpp> |
| #include <boost/type_traits/detail/bool_trait_undef.hpp> |
| |
| #endif // IS_LVALUE_ITERATOR_DWA2003112_HPP |