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 FACADE_ITERATOR_CATEGORY_DWA20031118_HPP |
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5 | # define FACADE_ITERATOR_CATEGORY_DWA20031118_HPP |
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6 | |
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7 | # include <boost/iterator/iterator_categories.hpp> |
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8 | |
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9 | # include <boost/mpl/or.hpp> // used in iterator_tag inheritance logic |
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10 | # include <boost/mpl/and.hpp> |
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11 | # include <boost/mpl/if.hpp> |
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12 | # include <boost/mpl/eval_if.hpp> |
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13 | # include <boost/mpl/identity.hpp> |
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14 | # include <boost/mpl/assert.hpp> |
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15 | |
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16 | # include <boost/type_traits/is_same.hpp> |
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17 | # include <boost/type_traits/is_const.hpp> |
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18 | # include <boost/type_traits/is_reference.hpp> |
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19 | # include <boost/type_traits/is_convertible.hpp> |
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20 | |
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21 | # include <boost/type_traits/is_same.hpp> |
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22 | |
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23 | # include <boost/iterator/detail/config_def.hpp> // try to keep this last |
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24 | |
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25 | # ifdef BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY |
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26 | # include <boost/detail/indirect_traits.hpp> |
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27 | # endif |
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28 | |
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29 | // |
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30 | // iterator_category deduction for iterator_facade |
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31 | // |
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32 | |
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33 | // forward declaration |
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34 | namespace boost { struct use_default; } |
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35 | |
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36 | namespace boost { namespace detail { |
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37 | |
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38 | struct input_output_iterator_tag |
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39 | : std::input_iterator_tag |
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40 | { |
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41 | // Using inheritance for only input_iterator_tag helps to avoid |
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42 | // ambiguities when a stdlib implementation dispatches on a |
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43 | // function which is overloaded on both input_iterator_tag and |
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44 | // output_iterator_tag, as STLPort does, in its __valid_range |
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45 | // function. I claim it's better to avoid the ambiguity in these |
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46 | // cases. |
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47 | operator std::output_iterator_tag() const |
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48 | { |
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49 | return std::output_iterator_tag(); |
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50 | } |
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51 | }; |
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52 | |
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53 | // |
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54 | // True iff the user has explicitly disabled writability of this |
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55 | // iterator. Pass the iterator_facade's Value parameter and its |
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56 | // nested ::reference type. |
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57 | // |
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58 | template <class ValueParam, class Reference> |
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59 | struct iterator_writability_disabled |
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60 | # ifdef BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY // Adding Thomas' logic? |
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61 | : mpl::or_< |
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62 | is_const<Reference> |
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63 | , boost::detail::indirect_traits::is_reference_to_const<Reference> |
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64 | , is_const<ValueParam> |
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65 | > |
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66 | # else |
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67 | : is_const<ValueParam> |
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68 | # endif |
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69 | {}; |
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70 | |
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71 | |
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72 | // |
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73 | // Convert an iterator_facade's traversal category, Value parameter, |
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74 | // and ::reference type to an appropriate old-style category. |
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75 | // |
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76 | // If writability has been disabled per the above metafunction, the |
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77 | // result will not be convertible to output_iterator_tag. |
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78 | // |
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79 | // Otherwise, if Traversal == single_pass_traversal_tag, the following |
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80 | // conditions will result in a tag that is convertible both to |
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81 | // input_iterator_tag and output_iterator_tag: |
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82 | // |
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83 | // 1. Reference is a reference to non-const |
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84 | // 2. Reference is not a reference and is convertible to Value |
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85 | // |
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86 | template <class Traversal, class ValueParam, class Reference> |
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87 | struct iterator_facade_default_category |
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88 | : mpl::eval_if< |
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89 | mpl::and_< |
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90 | is_reference<Reference> |
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91 | , is_convertible<Traversal,forward_traversal_tag> |
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92 | > |
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93 | , mpl::eval_if< |
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94 | is_convertible<Traversal,random_access_traversal_tag> |
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95 | , mpl::identity<std::random_access_iterator_tag> |
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96 | , mpl::if_< |
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97 | is_convertible<Traversal,bidirectional_traversal_tag> |
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98 | , std::bidirectional_iterator_tag |
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99 | , std::forward_iterator_tag |
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100 | > |
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101 | > |
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102 | , typename mpl::eval_if< |
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103 | mpl::and_< |
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104 | is_convertible<Traversal, single_pass_traversal_tag> |
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105 | |
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106 | // check for readability |
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107 | , is_convertible<Reference, ValueParam> |
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108 | > |
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109 | , mpl::identity<std::input_iterator_tag> |
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110 | , mpl::identity<Traversal> |
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111 | > |
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112 | > |
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113 | { |
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114 | }; |
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115 | |
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116 | // True iff T is convertible to an old-style iterator category. |
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117 | template <class T> |
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118 | struct is_iterator_category |
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119 | : mpl::or_< |
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120 | is_convertible<T,std::input_iterator_tag> |
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121 | , is_convertible<T,std::output_iterator_tag> |
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122 | > |
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123 | { |
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124 | }; |
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125 | |
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126 | template <class T> |
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127 | struct is_iterator_traversal |
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128 | : is_convertible<T,incrementable_traversal_tag> |
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129 | {}; |
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130 | |
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131 | // |
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132 | // A composite iterator_category tag convertible to Category (a pure |
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133 | // old-style category) and Traversal (a pure traversal tag). |
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134 | // Traversal must be a strict increase of the traversal power given by |
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135 | // Category. |
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136 | // |
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137 | template <class Category, class Traversal> |
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138 | struct iterator_category_with_traversal |
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139 | : Category, Traversal |
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140 | { |
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141 | # if !BOOST_WORKAROUND(BOOST_MSVC, <= 1300) |
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142 | // Make sure this isn't used to build any categories where |
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143 | // convertibility to Traversal is redundant. Should just use the |
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144 | // Category element in that case. |
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145 | BOOST_MPL_ASSERT_NOT(( |
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146 | is_convertible< |
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147 | typename iterator_category_to_traversal<Category>::type |
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148 | , Traversal |
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149 | >)); |
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150 | |
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151 | BOOST_MPL_ASSERT((is_iterator_category<Category>)); |
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152 | BOOST_MPL_ASSERT_NOT((is_iterator_category<Traversal>)); |
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153 | BOOST_MPL_ASSERT_NOT((is_iterator_traversal<Category>)); |
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154 | # if !BOOST_WORKAROUND(BOOST_MSVC, BOOST_TESTED_AT(1310)) |
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155 | BOOST_MPL_ASSERT((is_iterator_traversal<Traversal>)); |
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156 | # endif |
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157 | # endif |
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158 | }; |
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159 | |
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160 | // Computes an iterator_category tag whose traversal is Traversal and |
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161 | // which is appropriate for an iterator |
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162 | template <class Traversal, class ValueParam, class Reference> |
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163 | struct facade_iterator_category_impl |
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164 | { |
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165 | # if !BOOST_WORKAROUND(BOOST_MSVC, <= 1300) |
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166 | BOOST_MPL_ASSERT_NOT((is_iterator_category<Traversal>)); |
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167 | # endif |
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168 | |
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169 | typedef typename iterator_facade_default_category< |
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170 | Traversal,ValueParam,Reference |
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171 | >::type category; |
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172 | |
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173 | typedef typename mpl::if_< |
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174 | is_same< |
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175 | Traversal |
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176 | , typename iterator_category_to_traversal<category>::type |
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177 | > |
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178 | , category |
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179 | , iterator_category_with_traversal<category,Traversal> |
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180 | >::type type; |
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181 | }; |
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182 | |
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183 | // |
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184 | // Compute an iterator_category for iterator_facade |
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185 | // |
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186 | template <class CategoryOrTraversal, class ValueParam, class Reference> |
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187 | struct facade_iterator_category |
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188 | : mpl::eval_if< |
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189 | is_iterator_category<CategoryOrTraversal> |
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190 | , mpl::identity<CategoryOrTraversal> // old-style categories are fine as-is |
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191 | , facade_iterator_category_impl<CategoryOrTraversal,ValueParam,Reference> |
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192 | > |
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193 | { |
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194 | }; |
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195 | |
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196 | }} // namespace boost::detail |
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197 | |
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198 | # include <boost/iterator/detail/config_undef.hpp> |
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199 | |
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200 | #endif // FACADE_ITERATOR_CATEGORY_DWA20031118_HPP |
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