ceph/src/boost/libs/iterator/include/boost/iterator/detail/facade_iterator_category.hpp

   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 FACADE_ITERATOR_CATEGORY_DWA20031118_HPP
   5 # define FACADE_ITERATOR_CATEGORY_DWA20031118_HPP
   6
   7 # include <boost/iterator/iterator_categories.hpp>
   8
   9 # include <boost/mpl/or.hpp>  // used in iterator_tag inheritance logic
  10 # include <boost/mpl/and.hpp>
  11 # include <boost/mpl/if.hpp>
  12 # include <boost/mpl/eval_if.hpp>
  13 # include <boost/mpl/identity.hpp>
  14 # include <boost/mpl/assert.hpp>
  15
  16 # include <boost/type_traits/is_same.hpp>
  17 # include <boost/type_traits/is_const.hpp>
  18 # include <boost/type_traits/is_reference.hpp>
  19 # include <boost/type_traits/is_convertible.hpp>
  20
  21 # include <boost/type_traits/is_same.hpp>
  22
  23 # include <boost/iterator/detail/config_def.hpp> // try to keep this last
  24
  25 # ifdef BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY
  26 #  include <boost/detail/indirect_traits.hpp>
  27 # endif
  28
  29 //
  30 // iterator_category deduction for iterator_facade
  31 //
  32
  33 namespace boost {
  34 namespace iterators {
  35
  36 // forward declaration
  37 struct use_default;
  38
  39 namespace detail {
  40
  41 struct input_output_iterator_tag
  42   : std::input_iterator_tag
  43 {
  44     // Using inheritance for only input_iterator_tag helps to avoid
  45     // ambiguities when a stdlib implementation dispatches on a
  46     // function which is overloaded on both input_iterator_tag and
  47     // output_iterator_tag, as STLPort does, in its __valid_range
  48     // function.  I claim it's better to avoid the ambiguity in these
  49     // cases.
  50     operator std::output_iterator_tag() const
  51     {
  52         return std::output_iterator_tag();
  53     }
  54 };
  55
  56 //
  57 // True iff the user has explicitly disabled writability of this
  58 // iterator.  Pass the iterator_facade's Value parameter and its
  59 // nested ::reference type.
  60 //
  61 template <class ValueParam, class Reference>
  62 struct iterator_writability_disabled
  63 # ifdef BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY // Adding Thomas' logic?
  64   : mpl::or_<
  65         is_const<Reference>
  66       , boost::detail::indirect_traits::is_reference_to_const<Reference>
  67       , is_const<ValueParam>
  68     >
  69 # else
  70   : is_const<ValueParam>
  71 # endif
  72 {};
  73
  74
  75 //
  76 // Convert an iterator_facade's traversal category, Value parameter,
  77 // and ::reference type to an appropriate old-style category.
  78 //
  79 // Due to changeset 21683, this now never results in a category convertible
  80 // to output_iterator_tag.
  81 //
  82 // Change at: https://svn.boost.org/trac/boost/changeset/21683
  83 template <class Traversal, class ValueParam, class Reference>
  84 struct iterator_facade_default_category
  85   : mpl::eval_if<
  86         mpl::and_<
  87             is_reference<Reference>
  88           , is_convertible<Traversal,forward_traversal_tag>
  89         >
  90       , mpl::eval_if<
  91             is_convertible<Traversal,random_access_traversal_tag>
  92           , mpl::identity<std::random_access_iterator_tag>
  93           , mpl::if_<
  94                 is_convertible<Traversal,bidirectional_traversal_tag>
  95               , std::bidirectional_iterator_tag
  96               , std::forward_iterator_tag
  97             >
  98         >
  99       , typename mpl::eval_if<
 100             mpl::and_<
 101                 is_convertible<Traversal, single_pass_traversal_tag>
 102
 103                 // check for readability
 104               , is_convertible<Reference, ValueParam>
 105             >
 106           , mpl::identity<std::input_iterator_tag>
 107           , mpl::identity<Traversal>
 108         >
 109     >
 110 {
 111 };
 112
 113 // True iff T is convertible to an old-style iterator category.
 114 template <class T>
 115 struct is_iterator_category
 116   : mpl::or_<
 117         is_convertible<T,std::input_iterator_tag>
 118       , is_convertible<T,std::output_iterator_tag>
 119     >
 120 {
 121 };
 122
 123 template <class T>
 124 struct is_iterator_traversal
 125   : is_convertible<T,incrementable_traversal_tag>
 126 {};
 127
 128 //
 129 // A composite iterator_category tag convertible to Category (a pure
 130 // old-style category) and Traversal (a pure traversal tag).
 131 // Traversal must be a strict increase of the traversal power given by
 132 // Category.
 133 //
 134 template <class Category, class Traversal>
 135 struct iterator_category_with_traversal
 136   : Category, Traversal
 137 {
 138     // Make sure this isn't used to build any categories where
 139     // convertibility to Traversal is redundant.  Should just use the
 140     // Category element in that case.
 141     BOOST_MPL_ASSERT_NOT((
 142         is_convertible<
 143               typename iterator_category_to_traversal<Category>::type
 144             , Traversal
 145           >));
 146
 147     BOOST_MPL_ASSERT((is_iterator_category<Category>));
 148     BOOST_MPL_ASSERT_NOT((is_iterator_category<Traversal>));
 149     BOOST_MPL_ASSERT_NOT((is_iterator_traversal<Category>));
 150 #  if !BOOST_WORKAROUND(BOOST_MSVC, BOOST_TESTED_AT(1310))
 151     BOOST_MPL_ASSERT((is_iterator_traversal<Traversal>));
 152 #  endif
 153 };
 154
 155 // Computes an iterator_category tag whose traversal is Traversal and
 156 // which is appropriate for an iterator
 157 template <class Traversal, class ValueParam, class Reference>
 158 struct facade_iterator_category_impl
 159 {
 160     BOOST_MPL_ASSERT_NOT((is_iterator_category<Traversal>));
 161
 162     typedef typename iterator_facade_default_category<
 163         Traversal,ValueParam,Reference
 164     >::type category;
 165
 166     typedef typename mpl::if_<
 167         is_same<
 168             Traversal
 169           , typename iterator_category_to_traversal<category>::type
 170         >
 171       , category
 172       , iterator_category_with_traversal<category,Traversal>
 173     >::type type;
 174 };
 175
 176 //
 177 // Compute an iterator_category for iterator_facade
 178 //
 179 template <class CategoryOrTraversal, class ValueParam, class Reference>
 180 struct facade_iterator_category
 181   : mpl::eval_if<
 182         is_iterator_category<CategoryOrTraversal>
 183       , mpl::identity<CategoryOrTraversal> // old-style categories are fine as-is
 184       , facade_iterator_category_impl<CategoryOrTraversal,ValueParam,Reference>
 185     >
 186 {
 187 };
 188
 189 }}} // namespace boost::iterators::detail
 190
 191 # include <boost/iterator/detail/config_undef.hpp>
 192
 193 #endif // FACADE_ITERATOR_CATEGORY_DWA20031118_HPP