[857] | 1 | // Copyright David Abrahams 2003. Use, modification and distribution is
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| 2 | // subject to the Boost Software License, Version 1.0. (See accompanying
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| 3 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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| 4 | #ifndef IS_LVALUE_ITERATOR_DWA2003112_HPP
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| 5 | # define IS_LVALUE_ITERATOR_DWA2003112_HPP
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| 6 |
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| 7 | #include <boost/iterator.hpp>
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| 8 |
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| 9 | #include <boost/detail/workaround.hpp>
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| 10 | #include <boost/detail/iterator.hpp>
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| 11 |
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| 12 | #include <boost/iterator/detail/any_conversion_eater.hpp>
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| 13 |
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| 14 | // should be the last #includes
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| 15 | #include <boost/type_traits/detail/bool_trait_def.hpp>
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| 16 | #include <boost/iterator/detail/config_def.hpp>
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| 17 |
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| 18 | #ifndef BOOST_NO_IS_CONVERTIBLE
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| 19 |
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| 20 | namespace boost {
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| 21 |
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| 22 | namespace detail
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| 23 | {
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| 24 | #ifndef BOOST_NO_LVALUE_RETURN_DETECTION
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| 25 | // Calling lvalue_preserver( <expression>, 0 ) returns a reference
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| 26 | // to the expression's result if <expression> is an lvalue, or
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| 27 | // not_an_lvalue() otherwise.
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| 28 | struct not_an_lvalue {};
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| 29 |
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| 30 | template <class T>
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| 31 | T& lvalue_preserver(T&, int);
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| 32 |
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| 33 | template <class U>
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| 34 | not_an_lvalue lvalue_preserver(U const&, ...);
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| 35 |
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| 36 | # define BOOST_LVALUE_PRESERVER(expr) detail::lvalue_preserver(expr,0)
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| 37 |
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| 38 | #else
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| 39 |
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| 40 | # define BOOST_LVALUE_PRESERVER(expr) expr
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| 41 |
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| 42 | #endif
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| 43 |
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| 44 | // Guts of is_lvalue_iterator. Value is the iterator's value_type
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| 45 | // and the result is computed in the nested rebind template.
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| 46 | template <class Value>
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| 47 | struct is_lvalue_iterator_impl
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| 48 | {
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| 49 | // Eat implicit conversions so we don't report true for things
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| 50 | // convertible to Value const&
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| 51 | struct conversion_eater
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| 52 | {
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| 53 | conversion_eater(Value&);
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| 54 | };
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| 55 |
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| 56 | static char tester(conversion_eater, int);
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| 57 | static char (& tester(any_conversion_eater, ...) )[2];
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| 58 |
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| 59 | template <class It>
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| 60 | struct rebind
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| 61 | {
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| 62 | static It& x;
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| 63 |
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| 64 | BOOST_STATIC_CONSTANT(
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| 65 | bool
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| 66 | , value = (
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| 67 | sizeof(
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| 68 | is_lvalue_iterator_impl<Value>::tester(
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| 69 | BOOST_LVALUE_PRESERVER(*x), 0
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| 70 | )
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| 71 | ) == 1
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| 72 | )
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| 73 | );
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| 74 | };
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| 75 | };
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| 76 |
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| 77 | #undef BOOST_LVALUE_PRESERVER
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| 78 |
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| 79 | //
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| 80 | // void specializations to handle std input and output iterators
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| 81 | //
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| 82 | template <>
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| 83 | struct is_lvalue_iterator_impl<void>
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| 84 | {
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| 85 | template <class It>
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| 86 | struct rebind : boost::mpl::false_
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| 87 | {};
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| 88 | };
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| 89 |
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| 90 | #ifndef BOOST_NO_CV_VOID_SPECIALIZATIONS
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| 91 | template <>
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| 92 | struct is_lvalue_iterator_impl<const void>
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| 93 | {
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| 94 | template <class It>
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| 95 | struct rebind : boost::mpl::false_
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| 96 | {};
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| 97 | };
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| 98 |
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| 99 | template <>
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| 100 | struct is_lvalue_iterator_impl<volatile void>
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| 101 | {
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| 102 | template <class It>
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| 103 | struct rebind : boost::mpl::false_
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| 104 | {};
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| 105 | };
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| 106 |
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| 107 | template <>
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| 108 | struct is_lvalue_iterator_impl<const volatile void>
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| 109 | {
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| 110 | template <class It>
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| 111 | struct rebind : boost::mpl::false_
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| 112 | {};
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| 113 | };
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| 114 | #endif
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| 115 |
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| 116 | //
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| 117 | // This level of dispatching is required for Borland. We might save
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| 118 | // an instantiation by removing it for others.
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| 119 | //
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| 120 | template <class It>
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| 121 | struct is_readable_lvalue_iterator_impl
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| 122 | : is_lvalue_iterator_impl<
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| 123 | BOOST_DEDUCED_TYPENAME boost::detail::iterator_traits<It>::value_type const
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| 124 | >::template rebind<It>
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| 125 | {};
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| 126 |
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| 127 | template <class It>
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| 128 | struct is_non_const_lvalue_iterator_impl
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| 129 | : is_lvalue_iterator_impl<
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| 130 | BOOST_DEDUCED_TYPENAME boost::detail::iterator_traits<It>::value_type
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| 131 | >::template rebind<It>
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| 132 | {};
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| 133 | } // namespace detail
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| 134 |
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| 135 | // Define the trait with full mpl lambda capability and various broken
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| 136 | // compiler workarounds
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| 137 | BOOST_TT_AUX_BOOL_TRAIT_DEF1(
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| 138 | is_lvalue_iterator,T,::boost::detail::is_readable_lvalue_iterator_impl<T>::value)
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| 139 |
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| 140 | BOOST_TT_AUX_BOOL_TRAIT_DEF1(
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| 141 | is_non_const_lvalue_iterator,T,::boost::detail::is_non_const_lvalue_iterator_impl<T>::value)
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| 142 |
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| 143 | } // namespace boost
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| 144 |
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| 145 | #endif
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| 146 |
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| 147 | #include <boost/iterator/detail/config_undef.hpp>
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| 148 | #include <boost/type_traits/detail/bool_trait_undef.hpp>
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| 149 |
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| 150 | #endif // IS_LVALUE_ITERATOR_DWA2003112_HPP
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