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
26 #ifndef BOOST_NO_LVALUE_RETURN_DETECTION
27 // Calling lvalue_preserver( <expression>, 0 ) returns a reference
28 // to the expression's result if <expression> is an lvalue, or
29 // not_an_lvalue() otherwise.
30 struct not_an_lvalue {};
33 T& lvalue_preserver(T&, int);
36 not_an_lvalue lvalue_preserver(U const&, ...);
38 # define BOOST_LVALUE_PRESERVER(expr) detail::lvalue_preserver(expr,0)
42 # define BOOST_LVALUE_PRESERVER(expr) expr
46 // Guts of is_lvalue_iterator. Value is the iterator's value_type
47 // and the result is computed in the nested rebind template.
48 template <class Value>
49 struct is_lvalue_iterator_impl
51 // Eat implicit conversions so we don't report true for things
52 // convertible to Value const&
53 struct conversion_eater
55 conversion_eater(Value&);
58 static char tester(conversion_eater, int);
59 static char (& tester(any_conversion_eater, ...) )[2];
66 BOOST_STATIC_CONSTANT(
70 is_lvalue_iterator_impl<Value>::tester(
71 BOOST_LVALUE_PRESERVER(*x), 0
79 #undef BOOST_LVALUE_PRESERVER
82 // void specializations to handle std input and output iterators
85 struct is_lvalue_iterator_impl<void>
88 struct rebind : boost::mpl::false_
92 #ifndef BOOST_NO_CV_VOID_SPECIALIZATIONS
94 struct is_lvalue_iterator_impl<const void>
97 struct rebind : boost::mpl::false_
102 struct is_lvalue_iterator_impl<volatile void>
105 struct rebind : boost::mpl::false_
110 struct is_lvalue_iterator_impl<const volatile void>
113 struct rebind : boost::mpl::false_
119 // This level of dispatching is required for Borland. We might save
120 // an instantiation by removing it for others.
123 struct is_readable_lvalue_iterator_impl
124 : is_lvalue_iterator_impl<
125 BOOST_DEDUCED_TYPENAME boost::detail::iterator_traits<It>::value_type const
126 >::template rebind<It>
130 struct is_non_const_lvalue_iterator_impl
131 : is_lvalue_iterator_impl<
132 BOOST_DEDUCED_TYPENAME boost::detail::iterator_traits<It>::value_type
133 >::template rebind<It>
135 } // namespace detail
137 // Define the trait with full mpl lambda capability and various broken
138 // compiler workarounds
139 BOOST_TT_AUX_BOOL_TRAIT_DEF1(
140 is_lvalue_iterator,T,::boost::iterators::detail::is_readable_lvalue_iterator_impl<T>::value)
142 BOOST_TT_AUX_BOOL_TRAIT_DEF1(
143 is_non_const_lvalue_iterator,T,::boost::iterators::detail::is_non_const_lvalue_iterator_impl<T>::value)
145 } // namespace iterators
147 using iterators::is_lvalue_iterator;
148 using iterators::is_non_const_lvalue_iterator;
154 #include <boost/iterator/detail/config_undef.hpp>
155 #include <boost/type_traits/detail/bool_trait_undef.hpp>
157 #endif // IS_LVALUE_ITERATOR_DWA2003112_HPP