Merge pull request #4 from Lastique/sfinae-based-operators

Make iterator operators conditionally defined depending on its category.

Looks okay and fixes several known problems, thanks Andrey.

include/boost/iterator/iterator_facade.hpp

@@ -7,9 +7,11 @@
 #ifndef BOOST_ITERATOR_FACADE_23022003THW_HPP
 #define BOOST_ITERATOR_FACADE_23022003THW_HPP
 
+#include <boost/config.hpp>
 #include <boost/iterator.hpp>
 #include <boost/iterator/interoperable.hpp>
 #include <boost/iterator/iterator_traits.hpp>
+#include <boost/iterator/iterator_categories.hpp>
 
 #include <boost/iterator/detail/facade_iterator_category.hpp>
 #include <boost/iterator/detail/enable_if.hpp>
@@ -56,6 +58,12 @@ namespace boost
         };
     };
 
+    // The type trait checks if the category or traversal is at least as advanced as the specified required traversal
+    template< typename CategoryOrTraversal, typename Required >
+    struct is_traversal_at_least :
+        public boost::is_convertible< typename iterator_category_to_traversal< CategoryOrTraversal >::type, Required >
+    {};
+
     //
     // enable if for use in operator implementation.
     //
@@ -64,11 +72,27 @@ namespace boost
       , class Facade2
       , class Return
     >
-    struct enable_if_interoperable
-      : ::boost::iterators::enable_if<
-           mpl::or_<
-               is_convertible<Facade1, Facade2>
-             , is_convertible<Facade2, Facade1>
+    struct enable_if_interoperable :
+        public boost::iterators::enable_if<
+            is_interoperable< Facade1, Facade2 >
+          , Return
+        >
+    {};
+
+    //
+    // enable if for use in implementation of operators specific for random access traversal.
+    //
+    template <
+        class Facade1
+      , class Facade2
+      , class Return
+    >
+    struct enable_if_interoperable_and_random_access_traversal :
+        public boost::iterators::enable_if<
+            mpl::and_<
+                is_interoperable< Facade1, Facade2 >
+              , is_traversal_at_least< typename iterator_category< Facade1 >::type, random_access_traversal_tag >
+              , is_traversal_at_least< typename iterator_category< Facade2 >::type, random_access_traversal_tag >
             >
           , Return
         >
@@ -396,12 +420,24 @@ namespace boost
         {};
 
     };
+
+    template <
+        class Derived
+      , class Value
+      , class CategoryOrTraversal
+      , class Reference
+      , class Difference
+      , bool IsBidirectionalTraversal
+      , bool IsRandomAccessTraversal
+    >
+    class iterator_facade_base;
+
   } // namespace detail
 
 
   // Macros which describe the declarations of binary operators
 # ifdef BOOST_NO_STRICT_ITERATOR_INTEROPERABILITY
-#  define BOOST_ITERATOR_FACADE_INTEROP_HEAD(prefix, op, result_type)       \
+#  define BOOST_ITERATOR_FACADE_INTEROP_HEAD_IMPL(prefix, op, result_type, enabler)       \
     template <                                                              \
         class Derived1, class V1, class TC1, class Reference1, class Difference1 \
       , class Derived2, class V2, class TC2, class Reference2, class Difference2 \
@@ -411,12 +447,12 @@ namespace boost
         iterator_facade<Derived1, V1, TC1, Reference1, Difference1> const& lhs   \
       , iterator_facade<Derived2, V2, TC2, Reference2, Difference2> const& rhs)
 # else
-#  define BOOST_ITERATOR_FACADE_INTEROP_HEAD(prefix, op, result_type)   \
+#  define BOOST_ITERATOR_FACADE_INTEROP_HEAD_IMPL(prefix, op, result_type, enabler)   \
     template <                                                          \
         class Derived1, class V1, class TC1, class Reference1, class Difference1 \
       , class Derived2, class V2, class TC2, class Reference2, class Difference2 \
     >                                                                   \
-    prefix typename boost::detail::enable_if_interoperable<             \
+    prefix typename enabler<                                            \
         Derived1, Derived2                                              \
       , typename mpl::apply2<result_type,Derived1,Derived2>::type       \
     >::type                                                             \
@@ -425,9 +461,18 @@ namespace boost
       , iterator_facade<Derived2, V2, TC2, Reference2, Difference2> const& rhs)
 # endif
 
+#  define BOOST_ITERATOR_FACADE_INTEROP_HEAD(prefix, op, result_type)       \
+    BOOST_ITERATOR_FACADE_INTEROP_HEAD_IMPL(prefix, op, result_type, boost::detail::enable_if_interoperable)
+
+#  define BOOST_ITERATOR_FACADE_INTEROP_RANDOM_ACCESS_HEAD(prefix, op, result_type)       \
+    BOOST_ITERATOR_FACADE_INTEROP_HEAD_IMPL(prefix, op, result_type, boost::detail::enable_if_interoperable_and_random_access_traversal)
+
 #  define BOOST_ITERATOR_FACADE_PLUS_HEAD(prefix,args)              \
     template <class Derived, class V, class TC, class R, class D>   \
-    prefix Derived operator+ args
+    prefix typename boost::iterators::enable_if<                    \
+        boost::detail::is_traversal_at_least< TC, boost::random_access_traversal_tag >,  \
+        Derived                                                     \
+    >::type operator+ args
 
   //
   // Helper class for granting access to the iterator core interface.
@@ -447,6 +492,8 @@ namespace boost
 # else
 
       template <class I, class V, class TC, class R, class D> friend class iterator_facade;
+      template <class I, class V, class TC, class R, class D, bool IsBidirectionalTraversal, bool IsRandomAccessTraversal>
+      friend class detail::iterator_facade_base;
 
 #  define BOOST_ITERATOR_FACADE_RELATION(op)                                \
       BOOST_ITERATOR_FACADE_INTEROP_HEAD(friend,op, boost::detail::always_bool2);
@@ -454,13 +501,19 @@ namespace boost
       BOOST_ITERATOR_FACADE_RELATION(==)
       BOOST_ITERATOR_FACADE_RELATION(!=)
 
-      BOOST_ITERATOR_FACADE_RELATION(<)
-      BOOST_ITERATOR_FACADE_RELATION(>)
-      BOOST_ITERATOR_FACADE_RELATION(<=)
-      BOOST_ITERATOR_FACADE_RELATION(>=)
 #  undef BOOST_ITERATOR_FACADE_RELATION
 
-      BOOST_ITERATOR_FACADE_INTEROP_HEAD(
+#  define BOOST_ITERATOR_FACADE_RANDOM_ACCESS_RELATION(op)                                \
+      BOOST_ITERATOR_FACADE_INTEROP_RANDOM_ACCESS_HEAD(friend,op, boost::detail::always_bool2);
+
+      BOOST_ITERATOR_FACADE_RANDOM_ACCESS_RELATION(<)
+      BOOST_ITERATOR_FACADE_RANDOM_ACCESS_RELATION(>)
+      BOOST_ITERATOR_FACADE_RANDOM_ACCESS_RELATION(<=)
+      BOOST_ITERATOR_FACADE_RANDOM_ACCESS_RELATION(>=)
+
+#  undef BOOST_ITERATOR_FACADE_RANDOM_ACCESS_RELATION
+
+      BOOST_ITERATOR_FACADE_INTEROP_RANDOM_ACCESS_HEAD(
           friend, -, boost::detail::choose_difference_type)
       ;
 
@@ -545,23 +598,21 @@ namespace boost
           return *static_cast<I const*>(&facade);
       }
 
-   private:
       // objects of this class are useless
-      iterator_core_access(); //undefined
+      BOOST_DELETED_FUNCTION(iterator_core_access())
   };
 
-  //
-  // iterator_facade - use as a public base class for defining new
-  // standard-conforming iterators.
-  //
+  namespace detail {
+
+    // Implementation for forward traversal iterators
     template <
-      class Derived             // The derived iterator type being constructed
+        class Derived
       , class Value
       , class CategoryOrTraversal
-    , class Reference   = Value&
-    , class Difference  = std::ptrdiff_t
+      , class Reference
+      , class Difference
     >
-  class iterator_facade
+    class iterator_facade_base< Derived, Value, CategoryOrTraversal, Reference, Difference, false, false >
 # ifdef BOOST_ITERATOR_FACADE_NEEDS_ITERATOR_BASE
         : public boost::detail::iterator_facade_types<
              Value, CategoryOrTraversal, Reference, Difference
@@ -570,6 +621,42 @@ namespace boost
 # endif
     {
     private:
+        typedef boost::detail::iterator_facade_types<
+            Value, CategoryOrTraversal, Reference, Difference
+        > associated_types;
+
+        typedef boost::detail::operator_arrow_dispatch<
+            Reference
+          , typename associated_types::pointer
+        > operator_arrow_dispatch_;
+
+    public:
+        typedef typename associated_types::value_type value_type;
+        typedef Reference reference;
+        typedef Difference difference_type;
+
+        typedef typename operator_arrow_dispatch_::result_type pointer;
+
+        typedef typename associated_types::iterator_category iterator_category;
+
+    public:
+        reference operator*() const
+        {
+            return iterator_core_access::dereference(this->derived());
+        }
+
+        pointer operator->() const
+        {
+            return operator_arrow_dispatch_::apply(*this->derived());
+        }
+
+        Derived& operator++()
+        {
+            iterator_core_access::increment(this->derived());
+            return this->derived();
+        }
+
+    protected:
         //
         // Curiously Recurring Template interface.
         //
@@ -582,57 +669,20 @@ namespace boost
         {
             return *static_cast<Derived const*>(this);
         }
+    };
 
-      typedef boost::detail::iterator_facade_types<
-         Value, CategoryOrTraversal, Reference, Difference
-      > associated_types;
-
-      typedef boost::detail::operator_arrow_dispatch<
-          Reference
-        , typename associated_types::pointer
-      > operator_arrow_dispatch_;
-
-   protected:
-      // For use by derived classes
-      typedef iterator_facade<Derived,Value,CategoryOrTraversal,Reference,Difference> iterator_facade_;
-      
+    // Implementation for bidirectional traversal iterators
+    template <
+        class Derived
+      , class Value
+      , class CategoryOrTraversal
+      , class Reference
+      , class Difference
+    >
+    class iterator_facade_base< Derived, Value, CategoryOrTraversal, Reference, Difference, true, false > :
+        public iterator_facade_base< Derived, Value, CategoryOrTraversal, Reference, Difference, false, false >
+    {
     public:
-
-      typedef typename associated_types::value_type value_type;
-      typedef Reference reference;
-      typedef Difference difference_type;
-
-      typedef typename operator_arrow_dispatch_::result_type pointer;
-
-      typedef typename associated_types::iterator_category iterator_category;
-
-      reference operator*() const
-      {
-          return iterator_core_access::dereference(this->derived());
-      }
-
-      pointer operator->() const
-      {
-          return operator_arrow_dispatch_::apply(*this->derived());
-      }
-        
-      typename boost::detail::operator_brackets_result<Derived,Value,reference>::type
-      operator[](difference_type n) const
-      {
-          typedef boost::detail::use_operator_brackets_proxy<Value,Reference> use_proxy;
-          
-          return boost::detail::make_operator_brackets_result<Derived>(
-              this->derived() + n
-            , use_proxy()
-          );
-      }
-
-      Derived& operator++()
-      {
-          iterator_core_access::increment(this->derived());
-          return this->derived();
-      }
-
         Derived& operator--()
         {
             iterator_core_access::decrement(this->derived());
@@ -645,6 +695,37 @@ namespace boost
             --*this;
             return tmp;
         }
+    };
+
+    // Implementation for random access traversal iterators
+    template <
+        class Derived
+      , class Value
+      , class CategoryOrTraversal
+      , class Reference
+      , class Difference
+    >
+    class iterator_facade_base< Derived, Value, CategoryOrTraversal, Reference, Difference, true, true > :
+        public iterator_facade_base< Derived, Value, CategoryOrTraversal, Reference, Difference, true, false >
+    {
+    private:
+        typedef iterator_facade_base< Derived, Value, CategoryOrTraversal, Reference, Difference, true, false > base_type;
+
+    public:
+        typedef typename base_type::reference reference;
+        typedef typename base_type::difference_type difference_type;
+
+    public:
+        typename boost::detail::operator_brackets_result<Derived, Value, reference>::type
+        operator[](difference_type n) const
+        {
+            typedef boost::detail::use_operator_brackets_proxy<Value, Reference> use_proxy;
+
+            return boost::detail::make_operator_brackets_result<Derived>(
+                this->derived() + n
+              , use_proxy()
+            );
+        }
 
         Derived& operator+=(difference_type n)
         {
@@ -665,6 +746,35 @@ namespace boost
         }
     };
 
+  } // namespace detail
+
+  //
+  // iterator_facade - use as a public base class for defining new
+  // standard-conforming iterators.
+  //
+  template <
+      class Derived             // The derived iterator type being constructed
+    , class Value
+    , class CategoryOrTraversal
+    , class Reference   = Value&
+    , class Difference  = std::ptrdiff_t
+  >
+  class iterator_facade :
+      public detail::iterator_facade_base<
+          Derived,
+          Value,
+          CategoryOrTraversal,
+          Reference,
+          Difference,
+          detail::is_traversal_at_least< CategoryOrTraversal, bidirectional_traversal_tag >::value,
+          detail::is_traversal_at_least< CategoryOrTraversal, random_access_traversal_tag >::value
+      >
+  {
+  protected:
+      // For use by derived classes
+      typedef iterator_facade<Derived,Value,CategoryOrTraversal,Reference,Difference> iterator_facade_;
+  };
+
   template <class I, class V, class TC, class R, class D>
   inline typename boost::detail::postfix_increment_result<I,V,R,TC>::type
   operator++(
@@ -779,21 +889,50 @@ namespace boost
   BOOST_ITERATOR_FACADE_RELATION(==, return, equal)
   BOOST_ITERATOR_FACADE_RELATION(!=, return !, equal)
 
-  BOOST_ITERATOR_FACADE_RELATION(<, return 0 >, distance_from)
-  BOOST_ITERATOR_FACADE_RELATION(>, return 0 <, distance_from)
-  BOOST_ITERATOR_FACADE_RELATION(<=, return 0 >=, distance_from)
-  BOOST_ITERATOR_FACADE_RELATION(>=, return 0 <=, distance_from)
 # undef BOOST_ITERATOR_FACADE_RELATION
 
+
+# define BOOST_ITERATOR_FACADE_INTEROP_RANDOM_ACCESS(op, result_type, return_prefix, base_op) \
+  BOOST_ITERATOR_FACADE_INTEROP_RANDOM_ACCESS_HEAD(inline, op, result_type)                   \
+  {                                                                             \
+      /* For those compilers that do not support enable_if */                   \
+      BOOST_STATIC_ASSERT((                                                     \
+          is_interoperable< Derived1, Derived2 >::value &&                      \
+          boost::detail::is_traversal_at_least< typename iterator_category< Derived1 >::type, random_access_traversal_tag >::value && \
+          boost::detail::is_traversal_at_least< typename iterator_category< Derived2 >::type, random_access_traversal_tag >::value \
+      ));                                                                       \
+      return_prefix iterator_core_access::base_op(                              \
+          *static_cast<Derived1 const*>(&lhs)                                   \
+        , *static_cast<Derived2 const*>(&rhs)                                   \
+        , BOOST_ITERATOR_CONVERTIBLE(Derived2,Derived1)                         \
+      );                                                                        \
+  }
+
+# define BOOST_ITERATOR_FACADE_RANDOM_ACCESS_RELATION(op, return_prefix, base_op) \
+  BOOST_ITERATOR_FACADE_INTEROP_RANDOM_ACCESS(                                    \
+      op                                                            \
+    , boost::detail::always_bool2                                   \
+    , return_prefix                                                 \
+    , base_op                                                       \
+  )
+
+  BOOST_ITERATOR_FACADE_RANDOM_ACCESS_RELATION(<, return 0 >, distance_from)
+  BOOST_ITERATOR_FACADE_RANDOM_ACCESS_RELATION(>, return 0 <, distance_from)
+  BOOST_ITERATOR_FACADE_RANDOM_ACCESS_RELATION(<=, return 0 >=, distance_from)
+  BOOST_ITERATOR_FACADE_RANDOM_ACCESS_RELATION(>=, return 0 <=, distance_from)
+
+# undef BOOST_ITERATOR_FACADE_RANDOM_ACCESS_RELATION
+
   // operator- requires an additional part in the static assertion
-  BOOST_ITERATOR_FACADE_INTEROP(
+  BOOST_ITERATOR_FACADE_INTEROP_RANDOM_ACCESS(
       -
     , boost::detail::choose_difference_type
     , return
     , distance_from
   )
+
 # undef BOOST_ITERATOR_FACADE_INTEROP
-# undef BOOST_ITERATOR_FACADE_INTEROP_HEAD
+# undef BOOST_ITERATOR_FACADE_INTEROP_RANDOM_ACCESS
 
 # define BOOST_ITERATOR_FACADE_PLUS(args)           \
   BOOST_ITERATOR_FACADE_PLUS_HEAD(inline, args)     \
@@ -811,9 +950,14 @@ BOOST_ITERATOR_FACADE_PLUS((
     typename Derived::difference_type n
     , iterator_facade<Derived, V, TC, R, D> const& i
 ))
+
 # undef BOOST_ITERATOR_FACADE_PLUS
 # undef BOOST_ITERATOR_FACADE_PLUS_HEAD
 
+# undef BOOST_ITERATOR_FACADE_INTEROP_HEAD
+# undef BOOST_ITERATOR_FACADE_INTEROP_RANDOM_ACCESS_HEAD
+# undef BOOST_ITERATOR_FACADE_INTEROP_HEAD_IMPL
+
 } // namespace boost
 
 #include <boost/iterator/detail/config_undef.hpp>