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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