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
6
7#include <boost/iterator.hpp>
8
9#include <boost/detail/workaround.hpp>
10#include <boost/detail/iterator.hpp>
11
12#include <boost/type_traits/add_lvalue_reference.hpp>
13#include <boost/iterator/detail/any_conversion_eater.hpp>
14#include <boost/mpl/bool.hpp>
15#include <boost/mpl/aux_/lambda_support.hpp>
16
17// should be the last #includes
18#include <boost/type_traits/integral_constant.hpp>
19#include <boost/iterator/detail/config_def.hpp>
20
21#ifndef BOOST_NO_IS_CONVERTIBLE
22
23namespace boost {
24
25namespace iterators {
26
27namespace detail
28{
29#ifndef BOOST_NO_LVALUE_RETURN_DETECTION
30 // Calling lvalue_preserver( <expression>, 0 ) returns a reference
31 // to the expression's result if <expression> is an lvalue, or
32 // not_an_lvalue() otherwise.
33 struct not_an_lvalue {};
34
35 template <class T>
36 T& lvalue_preserver(T&, int);
37
38 template <class U>
39 not_an_lvalue lvalue_preserver(U const&, ...);
40
41# define BOOST_LVALUE_PRESERVER(expr) detail::lvalue_preserver(expr,0)
42
43#else
44
45# define BOOST_LVALUE_PRESERVER(expr) expr
46
47#endif
48
49 // Guts of is_lvalue_iterator. Value is the iterator's value_type
50 // and the result is computed in the nested rebind template.
51 template <class Value>
52 struct is_lvalue_iterator_impl
53 {
54 // Eat implicit conversions so we don't report true for things
55 // convertible to Value const&
56 struct conversion_eater
57 {
58 conversion_eater(typename add_lvalue_reference<Value>::type);
59 };
60
61 static char tester(conversion_eater, int);
62 static char (& tester(any_conversion_eater, ...) )[2];
63
64 template <class It>
65 struct rebind
66 {
67 static It& x;
68
69 BOOST_STATIC_CONSTANT(
70 bool
71 , value = (
72 sizeof(
73 is_lvalue_iterator_impl<Value>::tester(
74 BOOST_LVALUE_PRESERVER(*x), 0
75 )
76 ) == 1
77 )
78 );
79 };
80 };
81
82#undef BOOST_LVALUE_PRESERVER
83
84 //
85 // void specializations to handle std input and output iterators
86 //
87 template <>
88 struct is_lvalue_iterator_impl<void>
89 {
90 template <class It>
91 struct rebind : boost::mpl::false_
92 {};
93 };
94
95#ifndef BOOST_NO_CV_VOID_SPECIALIZATIONS
96 template <>
97 struct is_lvalue_iterator_impl<const void>
98 {
99 template <class It>
100 struct rebind : boost::mpl::false_
101 {};
102 };
103
104 template <>
105 struct is_lvalue_iterator_impl<volatile void>
106 {
107 template <class It>
108 struct rebind : boost::mpl::false_
109 {};
110 };
111
112 template <>
113 struct is_lvalue_iterator_impl<const volatile void>
114 {
115 template <class It>
116 struct rebind : boost::mpl::false_
117 {};
118 };
119#endif
120
121 //
122 // This level of dispatching is required for Borland. We might save
123 // an instantiation by removing it for others.
124 //
125 template <class It>
126 struct is_readable_lvalue_iterator_impl
127 : is_lvalue_iterator_impl<
128 BOOST_DEDUCED_TYPENAME boost::detail::iterator_traits<It>::value_type const
129 >::template rebind<It>
130 {};
131
132 template <class It>
133 struct is_non_const_lvalue_iterator_impl
134 : is_lvalue_iterator_impl<
135 BOOST_DEDUCED_TYPENAME boost::detail::iterator_traits<It>::value_type
136 >::template rebind<It>
137 {};
138} // namespace detail
139
140template< typename T > struct is_lvalue_iterator
141: public ::boost::integral_constant<bool,::boost::iterators::detail::is_readable_lvalue_iterator_impl<T>::value>
142{
143public:
144 BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_lvalue_iterator,(T))
145};
146
147template< typename T > struct is_non_const_lvalue_iterator
148: public ::boost::integral_constant<bool,::boost::iterators::detail::is_non_const_lvalue_iterator_impl<T>::value>
149{
150public:
151 BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_non_const_lvalue_iterator,(T))
152};
153
154} // namespace iterators
155
156using iterators::is_lvalue_iterator;
157using iterators::is_non_const_lvalue_iterator;
158
159} // namespace boost
160
161#endif
162
163#include <boost/iterator/detail/config_undef.hpp>
164
165#endif // IS_LVALUE_ITERATOR_DWA2003112_HPP
166

source code of boost/boost/iterator/is_lvalue_iterator.hpp