Reduced dependency on MPL in iterator_categories.hpp.

Also simplified implementation of type traits using Boost.MP11.

include/boost/iterator/iterator_categories.hpp

@@ -4,15 +4,13 @@
 // http://www.boost.org/LICENSE_1_0.txt)
 
 #ifndef BOOST_ITERATOR_CATEGORIES_HPP
-# define BOOST_ITERATOR_CATEGORIES_HPP
+#define BOOST_ITERATOR_CATEGORIES_HPP
 
-# include <boost/mpl/eval_if.hpp>
-# include <boost/mpl/identity.hpp>
-# include <boost/mpl/placeholders.hpp>
-# include <boost/mpl/aux_/lambda_support.hpp>
-
-#include <type_traits>
 #include <iterator>
+#include <type_traits>
+
+#include <boost/mpl/arg_fwd.hpp>
+#include <boost/mp11/utility.hpp>
 
 namespace boost {
 namespace iterators {
@@ -20,168 +18,78 @@ namespace iterators {
 //
 // Traversal Categories
 //
-
 struct no_traversal_tag {};
-
+struct incrementable_traversal_tag : public no_traversal_tag {};
-struct incrementable_traversal_tag
+struct single_pass_traversal_tag : public incrementable_traversal_tag {};
-  : no_traversal_tag
+struct forward_traversal_tag : public single_pass_traversal_tag {};
-{
+struct bidirectional_traversal_tag : public forward_traversal_tag {};
-//     incrementable_traversal_tag() {}
+struct random_access_traversal_tag : public bidirectional_traversal_tag {};
-//     incrementable_traversal_tag(std::output_iterator_tag const&) {};
-};
-
-struct single_pass_traversal_tag
-  : incrementable_traversal_tag
-{
-//     single_pass_traversal_tag() {}
-//     single_pass_traversal_tag(std::input_iterator_tag const&) {};
-};
-
-struct forward_traversal_tag
-  : single_pass_traversal_tag
-{
-//     forward_traversal_tag() {}
-//     forward_traversal_tag(std::forward_iterator_tag const&) {};
-};
-
-struct bidirectional_traversal_tag
-  : forward_traversal_tag
-{
-//     bidirectional_traversal_tag() {};
-//     bidirectional_traversal_tag(std::bidirectional_iterator_tag const&) {};
-};
-
-struct random_access_traversal_tag
-  : bidirectional_traversal_tag
-{
-//     random_access_traversal_tag() {};
-//     random_access_traversal_tag(std::random_access_iterator_tag const&) {};
-};
-
-namespace detail
-{
-  //
-  // Convert a "strictly old-style" iterator category to a traversal
-  // tag.  This is broken out into a separate metafunction to reduce
-  // the cost of instantiating iterator_category_to_traversal, below,
-  // for new-style types.
-  //
-  template <class Cat>
-  struct old_category_to_traversal
-    : mpl::eval_if<
-          std::is_convertible<Cat,std::random_access_iterator_tag>
-        , mpl::identity<random_access_traversal_tag>
-        , mpl::eval_if<
-              std::is_convertible<Cat,std::bidirectional_iterator_tag>
-            , mpl::identity<bidirectional_traversal_tag>
-            , mpl::eval_if<
-                  std::is_convertible<Cat,std::forward_iterator_tag>
-                , mpl::identity<forward_traversal_tag>
-                , mpl::eval_if<
-                      std::is_convertible<Cat,std::input_iterator_tag>
-                    , mpl::identity<single_pass_traversal_tag>
-                    , mpl::eval_if<
-                          std::is_convertible<Cat,std::output_iterator_tag>
-                        , mpl::identity<incrementable_traversal_tag>
-                        , void
-                      >
-                  >
-              >
-          >
-      >
-  {};
-
-} // namespace detail
 
 //
 // Convert an iterator category into a traversal tag
 //
-template <class Cat>
+template< typename Cat >
+using iterator_category_to_traversal_t = mp11::mp_cond<
+    // if already convertible to a traversal tag, we're done.
+    std::is_convertible< Cat, incrementable_traversal_tag >, Cat,
+    std::is_convertible< Cat, std::random_access_iterator_tag >, random_access_traversal_tag,
+    std::is_convertible< Cat, std::bidirectional_iterator_tag >, bidirectional_traversal_tag,
+    std::is_convertible< Cat, std::forward_iterator_tag >, forward_traversal_tag,
+    std::is_convertible< Cat, std::input_iterator_tag >, single_pass_traversal_tag,
+    std::is_convertible< Cat, std::output_iterator_tag >, incrementable_traversal_tag,
+    std::true_type, void
+>;
+
+template< typename Cat >
 struct iterator_category_to_traversal
-  : mpl::eval_if< // if already convertible to a traversal tag, we're done.
+{
-        std::is_convertible<Cat, incrementable_traversal_tag>
+    using type = iterator_category_to_traversal_t< Cat >;
-      , mpl::identity<Cat>
+};
-      , boost::iterators::detail::old_category_to_traversal<Cat>
-    >
-{};
 
 // Trait to get an iterator's traversal category
-template <class Iterator = mpl::_1>
+template< typename Iterator >
-struct iterator_traversal
+using iterator_traversal_t = iterator_category_to_traversal_t<
-  : iterator_category_to_traversal<
+    typename std::iterator_traits< Iterator >::iterator_category
-        typename std::iterator_traits<Iterator>::iterator_category
+>;
-    >
-{};
 
-# ifdef BOOST_MPL_CFG_NO_FULL_LAMBDA_SUPPORT
+template< typename Iterator = mpl::arg< 1 > >
-// Hack because BOOST_MPL_AUX_LAMBDA_SUPPORT doesn't seem to work
+struct iterator_traversal
-// out well.  Instantiating the nested apply template also
-// requires instantiating iterator_traits on the
-// placeholder. Instead we just specialize it as a metafunction
-// class.
-template <>
-struct iterator_traversal<mpl::_1>
 {
-    template <class T>
+    using type = iterator_traversal_t< Iterator >;
-    struct apply : iterator_traversal<T>
-    {};
 };
-template <>
-struct iterator_traversal<mpl::_>
-  : iterator_traversal<mpl::_1>
-{};
-# endif
 
 //
 // Convert an iterator traversal to one of the traversal tags.
 //
-template <class Traversal>
+template< typename Traversal >
+using pure_traversal_tag_t = mp11::mp_cond<
+    std::is_convertible< Traversal, random_access_traversal_tag >, random_access_traversal_tag,
+    std::is_convertible< Traversal, bidirectional_traversal_tag >, bidirectional_traversal_tag,
+    std::is_convertible< Traversal, forward_traversal_tag >, forward_traversal_tag,
+    std::is_convertible< Traversal, single_pass_traversal_tag >, single_pass_traversal_tag,
+    std::is_convertible< Traversal, incrementable_traversal_tag >, incrementable_traversal_tag,
+    std::true_type, void
+>;
+
+template< typename Traversal >
 struct pure_traversal_tag
-  : mpl::eval_if<
-        std::is_convertible<Traversal,random_access_traversal_tag>
-      , mpl::identity<random_access_traversal_tag>
-      , mpl::eval_if<
-            std::is_convertible<Traversal,bidirectional_traversal_tag>
-          , mpl::identity<bidirectional_traversal_tag>
-          , mpl::eval_if<
-                std::is_convertible<Traversal,forward_traversal_tag>
-              , mpl::identity<forward_traversal_tag>
-              , mpl::eval_if<
-                    std::is_convertible<Traversal,single_pass_traversal_tag>
-                  , mpl::identity<single_pass_traversal_tag>
-                  , mpl::eval_if<
-                        std::is_convertible<Traversal,incrementable_traversal_tag>
-                      , mpl::identity<incrementable_traversal_tag>
-                      , void
-                    >
-                >
-            >
-        >
-    >
 {
+    using type = pure_traversal_tag_t< Traversal >;
 };
 
 //
 // Trait to retrieve one of the iterator traversal tags from the iterator category or traversal.
 //
-template <class Iterator = mpl::_1>
+template< typename Iterator >
-struct pure_iterator_traversal
+using pure_iterator_traversal_t = pure_traversal_tag_t<
-  : pure_traversal_tag<typename iterator_traversal<Iterator>::type>
+    iterator_traversal_t< Iterator >
-{};
+>;
 
-# ifdef BOOST_MPL_CFG_NO_FULL_LAMBDA_SUPPORT
+template< typename Iterator = mpl::arg< 1 > >
-template <>
+struct pure_iterator_traversal
-struct pure_iterator_traversal<mpl::_1>
 {
-    template <class T>
+    using type = pure_iterator_traversal_t< Iterator >;
-    struct apply : pure_iterator_traversal<T>
-    {};
 };
-template <>
-struct pure_iterator_traversal<mpl::_>
-  : pure_iterator_traversal<mpl::_1>
-{};
-# endif
 
 } // namespace iterators
 
@@ -194,13 +102,6 @@ using iterators::random_access_traversal_tag;
 using iterators::iterator_category_to_traversal;
 using iterators::iterator_traversal;
 
-// This import is needed for backward compatibility with Boost.Range:
-// boost/range/detail/demote_iterator_traversal_tag.hpp
-// It should be removed when that header is fixed.
-namespace detail {
-using iterators::pure_traversal_tag;
-} // namespace detail
-
 } // namespace boost
 
 #endif // BOOST_ITERATOR_CATEGORIES_HPP