1 // Copyright David Abrahams 2003. Use, modification and distribution is
2 // subject to the Boost Software License, Version 1.0. (See accompanying
3 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
4 #ifndef IS_LVALUE_ITERATOR_DWA2003112_HPP
5 # define IS_LVALUE_ITERATOR_DWA2003112_HPP
7 #include <boost/iterator.hpp>
9 #include <boost/detail/workaround.hpp>
10 #include <boost/detail/iterator.hpp>
12 #include <boost/iterator/detail/any_conversion_eater.hpp>
14 // should be the last #includes
15 #include <boost/type_traits/detail/bool_trait_def.hpp>
16 #include <boost/iterator/detail/config_def.hpp>
18 #ifndef BOOST_NO_IS_CONVERTIBLE
24 #ifndef BOOST_NO_LVALUE_RETURN_DETECTION
25 // Calling lvalue_preserver( <expression>, 0 ) returns a reference
26 // to the expression's result if <expression> is an lvalue, or
27 // not_an_lvalue() otherwise.
28 struct not_an_lvalue {};
31 T& lvalue_preserver(T&, int);
34 not_an_lvalue lvalue_preserver(U const&, ...);
36 # define BOOST_LVALUE_PRESERVER(expr) detail::lvalue_preserver(expr,0)
40 # define BOOST_LVALUE_PRESERVER(expr) expr
44 // Guts of is_lvalue_iterator. Value is the iterator's value_type
45 // and the result is computed in the nested rebind template.
46 template <class Value>
47 struct is_lvalue_iterator_impl
49 // Eat implicit conversions so we don't report true for things
50 // convertible to Value const&
51 struct conversion_eater
53 conversion_eater(Value&);
56 static char tester(conversion_eater, int);
57 static char (& tester(any_conversion_eater, ...) )[2];
64 BOOST_STATIC_CONSTANT(
68 is_lvalue_iterator_impl<Value>::tester(
69 BOOST_LVALUE_PRESERVER(*x), 0
77 #undef BOOST_LVALUE_PRESERVER
80 // void specializations to handle std input and output iterators
83 struct is_lvalue_iterator_impl<void>
86 struct rebind : boost::mpl::false_
90 #ifndef BOOST_NO_CV_VOID_SPECIALIZATIONS
92 struct is_lvalue_iterator_impl<const void>
95 struct rebind : boost::mpl::false_
100 struct is_lvalue_iterator_impl<volatile void>
103 struct rebind : boost::mpl::false_
108 struct is_lvalue_iterator_impl<const volatile void>
111 struct rebind : boost::mpl::false_
117 // This level of dispatching is required for Borland. We might save
118 // an instantiation by removing it for others.
121 struct is_readable_lvalue_iterator_impl
122 : is_lvalue_iterator_impl<
123 BOOST_DEDUCED_TYPENAME boost::detail::iterator_traits<It>::value_type const
124 >::template rebind<It>
128 struct is_non_const_lvalue_iterator_impl
129 : is_lvalue_iterator_impl<
130 BOOST_DEDUCED_TYPENAME boost::detail::iterator_traits<It>::value_type
131 >::template rebind<It>
133 } // namespace detail
135 // Define the trait with full mpl lambda capability and various broken
136 // compiler workarounds
137 BOOST_TT_AUX_BOOL_TRAIT_DEF1(
138 is_lvalue_iterator,T,::boost::detail::is_readable_lvalue_iterator_impl<T>::value)
140 BOOST_TT_AUX_BOOL_TRAIT_DEF1(
141 is_non_const_lvalue_iterator,T,::boost::detail::is_non_const_lvalue_iterator_impl<T>::value)
147 #include <boost/iterator/detail/config_undef.hpp>
148 #include <boost/type_traits/detail/bool_trait_undef.hpp>
150 #endif // IS_LVALUE_ITERATOR_DWA2003112_HPP