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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 |