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- // Copyright David Abrahams 2003. Use, modification and distribution is
- // subject to the Boost Software License, Version 1.0. (See accompanying
- // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
- #ifndef FACADE_ITERATOR_CATEGORY_DWA20031118_HPP
- # define FACADE_ITERATOR_CATEGORY_DWA20031118_HPP
- # include <boost/core/use_default.hpp>
- # include <boost/iterator/iterator_categories.hpp>
- # include <boost/mpl/or.hpp> // used in iterator_tag inheritance logic
- # include <boost/mpl/and.hpp>
- # include <boost/mpl/if.hpp>
- # include <boost/mpl/eval_if.hpp>
- # include <boost/mpl/identity.hpp>
- # include <boost/mpl/assert.hpp>
- # include <boost/type_traits/is_same.hpp>
- # include <boost/type_traits/is_const.hpp>
- # include <boost/type_traits/is_reference.hpp>
- # include <boost/type_traits/is_convertible.hpp>
- # include <boost/type_traits/is_same.hpp>
- # include <boost/iterator/detail/config_def.hpp> // try to keep this last
- # ifdef BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY
- # include <boost/detail/indirect_traits.hpp>
- # endif
- //
- // iterator_category deduction for iterator_facade
- //
- namespace boost {
- namespace iterators {
- using boost::use_default;
- namespace detail {
- struct input_output_iterator_tag
- : std::input_iterator_tag
- {
- // Using inheritance for only input_iterator_tag helps to avoid
- // ambiguities when a stdlib implementation dispatches on a
- // function which is overloaded on both input_iterator_tag and
- // output_iterator_tag, as STLPort does, in its __valid_range
- // function. I claim it's better to avoid the ambiguity in these
- // cases.
- operator std::output_iterator_tag() const
- {
- return std::output_iterator_tag();
- }
- };
- //
- // True iff the user has explicitly disabled writability of this
- // iterator. Pass the iterator_facade's Value parameter and its
- // nested ::reference type.
- //
- template <class ValueParam, class Reference>
- struct iterator_writability_disabled
- # ifdef BOOST_ITERATOR_REF_CONSTNESS_KILLS_WRITABILITY // Adding Thomas' logic?
- : mpl::or_<
- is_const<Reference>
- , boost::detail::indirect_traits::is_reference_to_const<Reference>
- , is_const<ValueParam>
- >
- # else
- : is_const<ValueParam>
- # endif
- {};
- //
- // Convert an iterator_facade's traversal category, Value parameter,
- // and ::reference type to an appropriate old-style category.
- //
- // Due to changeset 21683, this now never results in a category convertible
- // to output_iterator_tag.
- //
- // Change at: https://svn.boost.org/trac/boost/changeset/21683
- template <class Traversal, class ValueParam, class Reference>
- struct iterator_facade_default_category
- : mpl::eval_if<
- mpl::and_<
- is_reference<Reference>
- , is_convertible<Traversal,forward_traversal_tag>
- >
- , mpl::eval_if<
- is_convertible<Traversal,random_access_traversal_tag>
- , mpl::identity<std::random_access_iterator_tag>
- , mpl::if_<
- is_convertible<Traversal,bidirectional_traversal_tag>
- , std::bidirectional_iterator_tag
- , std::forward_iterator_tag
- >
- >
- , typename mpl::eval_if<
- mpl::and_<
- is_convertible<Traversal, single_pass_traversal_tag>
- // check for readability
- , is_convertible<Reference, ValueParam>
- >
- , mpl::identity<std::input_iterator_tag>
- , mpl::identity<Traversal>
- >
- >
- {
- };
- // True iff T is convertible to an old-style iterator category.
- template <class T>
- struct is_iterator_category
- : mpl::or_<
- is_convertible<T,std::input_iterator_tag>
- , is_convertible<T,std::output_iterator_tag>
- >
- {
- };
- template <class T>
- struct is_iterator_traversal
- : is_convertible<T,incrementable_traversal_tag>
- {};
- //
- // A composite iterator_category tag convertible to Category (a pure
- // old-style category) and Traversal (a pure traversal tag).
- // Traversal must be a strict increase of the traversal power given by
- // Category.
- //
- template <class Category, class Traversal>
- struct iterator_category_with_traversal
- : Category, Traversal
- {
- // Make sure this isn't used to build any categories where
- // convertibility to Traversal is redundant. Should just use the
- // Category element in that case.
- BOOST_MPL_ASSERT_NOT((
- is_convertible<
- typename iterator_category_to_traversal<Category>::type
- , Traversal
- >));
- BOOST_MPL_ASSERT((is_iterator_category<Category>));
- BOOST_MPL_ASSERT_NOT((is_iterator_category<Traversal>));
- BOOST_MPL_ASSERT_NOT((is_iterator_traversal<Category>));
- # if !BOOST_WORKAROUND(BOOST_MSVC, BOOST_TESTED_AT(1310))
- BOOST_MPL_ASSERT((is_iterator_traversal<Traversal>));
- # endif
- };
- // Computes an iterator_category tag whose traversal is Traversal and
- // which is appropriate for an iterator
- template <class Traversal, class ValueParam, class Reference>
- struct facade_iterator_category_impl
- {
- BOOST_MPL_ASSERT_NOT((is_iterator_category<Traversal>));
- typedef typename iterator_facade_default_category<
- Traversal,ValueParam,Reference
- >::type category;
- typedef typename mpl::if_<
- is_same<
- Traversal
- , typename iterator_category_to_traversal<category>::type
- >
- , category
- , iterator_category_with_traversal<category,Traversal>
- >::type type;
- };
- //
- // Compute an iterator_category for iterator_facade
- //
- template <class CategoryOrTraversal, class ValueParam, class Reference>
- struct facade_iterator_category
- : mpl::eval_if<
- is_iterator_category<CategoryOrTraversal>
- , mpl::identity<CategoryOrTraversal> // old-style categories are fine as-is
- , facade_iterator_category_impl<CategoryOrTraversal,ValueParam,Reference>
- >
- {
- };
- }}} // namespace boost::iterators::detail
- # include <boost/iterator/detail/config_undef.hpp>
- #endif // FACADE_ITERATOR_CATEGORY_DWA20031118_HPP
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