]> git.donarmstrong.com Git - rsem.git/blobdiff - boost/iterator/iterator_facade.hpp
Updated boost to v1.55.0
[rsem.git] / boost / iterator / iterator_facade.hpp
diff --git a/boost/iterator/iterator_facade.hpp b/boost/iterator/iterator_facade.hpp
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+// (C) Copyright David Abrahams 2002.
+// (C) Copyright Jeremy Siek    2002.
+// (C) Copyright Thomas Witt    2002.
+// Distributed under 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 BOOST_ITERATOR_FACADE_23022003THW_HPP
+#define BOOST_ITERATOR_FACADE_23022003THW_HPP
+
+#include <boost/iterator.hpp>
+#include <boost/iterator/interoperable.hpp>
+#include <boost/iterator/iterator_traits.hpp>
+
+#include <boost/iterator/detail/facade_iterator_category.hpp>
+#include <boost/iterator/detail/enable_if.hpp>
+
+#include <boost/static_assert.hpp>
+#include <boost/utility/addressof.hpp>
+
+#include <boost/type_traits/is_same.hpp>
+#include <boost/type_traits/add_const.hpp>
+#include <boost/type_traits/add_pointer.hpp>
+#include <boost/type_traits/remove_const.hpp>
+#include <boost/type_traits/remove_reference.hpp>
+#include <boost/type_traits/is_convertible.hpp>
+#include <boost/type_traits/is_pod.hpp>
+
+#include <boost/mpl/eval_if.hpp>
+#include <boost/mpl/if.hpp>
+#include <boost/mpl/or.hpp>
+#include <boost/mpl/and.hpp>
+#include <boost/mpl/not.hpp>
+#include <boost/mpl/always.hpp>
+#include <boost/mpl/apply.hpp>
+#include <boost/mpl/identity.hpp>
+
+#include <boost/iterator/detail/config_def.hpp> // this goes last
+
+namespace boost
+{
+  // This forward declaration is required for the friend declaration
+  // in iterator_core_access
+  template <class I, class V, class TC, class R, class D> class iterator_facade;
+
+  namespace detail
+  {
+    // A binary metafunction class that always returns bool.  VC6
+    // ICEs on mpl::always<bool>, probably because of the default
+    // parameters.
+    struct always_bool2
+    {
+        template <class T, class U>
+        struct apply
+        {
+            typedef bool type;
+        };
+    };
+
+    //
+    // enable if for use in operator implementation.
+    //
+    template <
+        class Facade1
+      , class Facade2
+      , class Return
+    >
+    struct enable_if_interoperable
+#if BOOST_WORKAROUND(BOOST_MSVC, <= 1300)
+    {
+        typedef typename mpl::if_<
+            mpl::or_<
+                is_convertible<Facade1, Facade2>
+              , is_convertible<Facade2, Facade1>
+            >
+          , Return
+          , int[3]
+        >::type type;
+    };        
+#else
+      : ::boost::iterators::enable_if<
+           mpl::or_<
+               is_convertible<Facade1, Facade2>
+             , is_convertible<Facade2, Facade1>
+           >
+         , Return
+        >
+    {};
+#endif 
+
+    //
+    // Generates associated types for an iterator_facade with the
+    // given parameters.
+    //
+    template <
+        class ValueParam
+      , class CategoryOrTraversal
+      , class Reference 
+      , class Difference
+    >
+    struct iterator_facade_types
+    {
+        typedef typename facade_iterator_category<
+            CategoryOrTraversal, ValueParam, Reference
+        >::type iterator_category;
+        
+        typedef typename remove_const<ValueParam>::type value_type;
+        
+        // Not the real associated pointer type
+        typedef typename mpl::eval_if<
+            boost::detail::iterator_writability_disabled<ValueParam,Reference>
+          , add_pointer<const value_type>
+          , add_pointer<value_type>
+        >::type pointer;
+      
+# if defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)                          \
+    && (BOOST_WORKAROUND(_STLPORT_VERSION, BOOST_TESTED_AT(0x452))              \
+        || BOOST_WORKAROUND(BOOST_DINKUMWARE_STDLIB, BOOST_TESTED_AT(310)))     \
+    || BOOST_WORKAROUND(BOOST_RWSTD_VER, BOOST_TESTED_AT(0x20101))              \
+    || BOOST_WORKAROUND(BOOST_DINKUMWARE_STDLIB, <= 310)
+
+        // To interoperate with some broken library/compiler
+        // combinations, user-defined iterators must be derived from
+        // std::iterator.  It is possible to implement a standard
+        // library for broken compilers without this limitation.
+#  define BOOST_ITERATOR_FACADE_NEEDS_ITERATOR_BASE 1
+
+        typedef
+           iterator<iterator_category, value_type, Difference, pointer, Reference>
+        base;
+# endif
+    };
+
+    // iterators whose dereference operators reference the same value
+    // for all iterators into the same sequence (like many input
+    // iterators) need help with their postfix ++: the referenced
+    // value must be read and stored away before the increment occurs
+    // so that *a++ yields the originally referenced element and not
+    // the next one.
+    template <class Iterator>
+    class postfix_increment_proxy
+    {
+        typedef typename iterator_value<Iterator>::type value_type;
+     public:
+        explicit postfix_increment_proxy(Iterator const& x)
+          : stored_value(*x)
+        {}
+
+        // Returning a mutable reference allows nonsense like
+        // (*r++).mutate(), but it imposes fewer assumptions about the
+        // behavior of the value_type.  In particular, recall that
+        // (*r).mutate() is legal if operator* returns by value.
+        value_type&
+        operator*() const
+        {
+            return this->stored_value;
+        }
+     private:
+        mutable value_type stored_value;
+    };
+    
+    //
+    // In general, we can't determine that such an iterator isn't
+    // writable -- we also need to store a copy of the old iterator so
+    // that it can be written into.
+    template <class Iterator>
+    class writable_postfix_increment_proxy
+    {
+        typedef typename iterator_value<Iterator>::type value_type;
+     public:
+        explicit writable_postfix_increment_proxy(Iterator const& x)
+          : stored_value(*x)
+          , stored_iterator(x)
+        {}
+
+        // Dereferencing must return a proxy so that both *r++ = o and
+        // value_type(*r++) can work.  In this case, *r is the same as
+        // *r++, and the conversion operator below is used to ensure
+        // readability.
+        writable_postfix_increment_proxy const&
+        operator*() const
+        {
+            return *this;
+        }
+
+        // Provides readability of *r++
+        operator value_type&() const
+        {
+            return stored_value;
+        }
+
+        // Provides writability of *r++
+        template <class T>
+        T const& operator=(T const& x) const
+        {
+            *this->stored_iterator = x;
+            return x;
+        }
+
+        // This overload just in case only non-const objects are writable
+        template <class T>
+        T& operator=(T& x) const
+        {
+            *this->stored_iterator = x;
+            return x;
+        }
+
+        // Provides X(r++)
+        operator Iterator const&() const
+        {
+            return stored_iterator;
+        }
+        
+     private:
+        mutable value_type stored_value;
+        Iterator stored_iterator;
+    };
+
+# ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
+
+    template <class Reference, class Value>
+    struct is_non_proxy_reference_impl
+    {
+        static Reference r;
+        
+        template <class R>
+        static typename mpl::if_<
+            is_convertible<
+                R const volatile*
+              , Value const volatile*
+            >
+          , char[1]
+          , char[2]
+        >::type& helper(R const&);
+        
+        BOOST_STATIC_CONSTANT(bool, value = sizeof(helper(r)) == 1);
+    };
+        
+    template <class Reference, class Value>
+    struct is_non_proxy_reference
+      : mpl::bool_<
+            is_non_proxy_reference_impl<Reference, Value>::value
+        >
+    {};
+# else 
+    template <class Reference, class Value>
+    struct is_non_proxy_reference
+      : is_convertible<
+            typename remove_reference<Reference>::type
+            const volatile*
+          , Value const volatile*
+        >
+    {};
+# endif 
+        
+    // A metafunction to choose the result type of postfix ++
+    //
+    // Because the C++98 input iterator requirements say that *r++ has
+    // type T (value_type), implementations of some standard
+    // algorithms like lexicographical_compare may use constructions
+    // like:
+    //
+    //          *r++ < *s++
+    //
+    // If *r++ returns a proxy (as required if r is writable but not
+    // multipass), this sort of expression will fail unless the proxy
+    // supports the operator<.  Since there are any number of such
+    // operations, we're not going to try to support them.  Therefore,
+    // even if r++ returns a proxy, *r++ will only return a proxy if
+    // *r also returns a proxy.
+    template <class Iterator, class Value, class Reference, class CategoryOrTraversal>
+    struct postfix_increment_result
+      : mpl::eval_if<
+            mpl::and_<
+                // A proxy is only needed for readable iterators
+                is_convertible<Reference,Value const&>
+                
+                // No multipass iterator can have values that disappear
+                // before positions can be re-visited
+              , mpl::not_<
+                    is_convertible<
+                        typename iterator_category_to_traversal<CategoryOrTraversal>::type
+                      , forward_traversal_tag
+                    >
+                >
+            >
+          , mpl::if_<
+                is_non_proxy_reference<Reference,Value>
+              , postfix_increment_proxy<Iterator>
+              , writable_postfix_increment_proxy<Iterator>
+            >
+          , mpl::identity<Iterator>
+        >
+    {};
+
+    // operator->() needs special support for input iterators to strictly meet the
+    // standard's requirements. If *i is not a reference type, we must still
+    // produce an lvalue to which a pointer can be formed.  We do that by
+    // returning a proxy object containing an instance of the reference object.
+    template <class Reference, class Pointer>
+    struct operator_arrow_dispatch // proxy references
+    {
+        struct proxy
+        {
+            explicit proxy(Reference const & x) : m_ref(x) {}
+            Reference* operator->() { return boost::addressof(m_ref); }
+            // This function is needed for MWCW and BCC, which won't call
+            // operator-> again automatically per 13.3.1.2 para 8
+            operator Reference*() { return boost::addressof(m_ref); }
+            Reference m_ref;
+        };
+        typedef proxy result_type;
+        static result_type apply(Reference const & x)
+        {
+            return result_type(x);
+        }
+    };
+
+    template <class T, class Pointer>
+    struct operator_arrow_dispatch<T&, Pointer> // "real" references
+    {
+        typedef Pointer result_type;
+        static result_type apply(T& x)
+        {
+            return boost::addressof(x);
+        }
+    };
+
+# if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
+    // Deal with ETI
+    template<>
+    struct operator_arrow_dispatch<int, int>
+    {
+        typedef int result_type;
+    };
+# endif
+
+    // A proxy return type for operator[], needed to deal with
+    // iterators that may invalidate referents upon destruction.
+    // Consider the temporary iterator in *(a + n)
+    template <class Iterator>
+    class operator_brackets_proxy
+    {
+        // Iterator is actually an iterator_facade, so we do not have to
+        // go through iterator_traits to access the traits.
+        typedef typename Iterator::reference  reference;
+        typedef typename Iterator::value_type value_type;
+
+     public:
+        operator_brackets_proxy(Iterator const& iter)
+          : m_iter(iter)
+        {}
+
+        operator reference() const
+        {
+            return *m_iter;
+        }
+
+        operator_brackets_proxy& operator=(value_type const& val)
+        {
+            *m_iter = val;
+            return *this;
+        }
+
+     private:
+        Iterator m_iter;
+    };
+
+    // A metafunction that determines whether operator[] must return a
+    // proxy, or whether it can simply return a copy of the value_type.
+    template <class ValueType, class Reference>
+    struct use_operator_brackets_proxy
+      : mpl::not_<
+            mpl::and_<
+                // Really we want an is_copy_constructible trait here,
+                // but is_POD will have to suffice in the meantime.
+                boost::is_POD<ValueType>
+              , iterator_writability_disabled<ValueType,Reference>
+            >
+        >
+    {};
+        
+    template <class Iterator, class Value, class Reference>
+    struct operator_brackets_result
+    {
+        typedef typename mpl::if_<
+            use_operator_brackets_proxy<Value,Reference>
+          , operator_brackets_proxy<Iterator>
+          , Value
+        >::type type;
+    };
+
+    template <class Iterator>
+    operator_brackets_proxy<Iterator> make_operator_brackets_result(Iterator const& iter, mpl::true_)
+    {
+        return operator_brackets_proxy<Iterator>(iter);
+    }
+
+    template <class Iterator>
+    typename Iterator::value_type make_operator_brackets_result(Iterator const& iter, mpl::false_)
+    {
+      return *iter;
+    }
+
+    struct choose_difference_type
+    {
+        template <class I1, class I2>
+        struct apply
+          :
+# ifdef BOOST_NO_ONE_WAY_ITERATOR_INTEROP
+          iterator_difference<I1>
+# elif BOOST_WORKAROUND(BOOST_MSVC, < 1300)
+          mpl::if_<
+              is_convertible<I2,I1>
+            , typename I1::difference_type
+            , typename I2::difference_type
+          >
+# else 
+          mpl::eval_if<
+              is_convertible<I2,I1>
+            , iterator_difference<I1>
+            , iterator_difference<I2>
+          >
+# endif 
+        {};
+
+    };
+  } // 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)       \
+    template <                                                              \
+        class Derived1, class V1, class TC1, class Reference1, class Difference1 \
+      , class Derived2, class V2, class TC2, class Reference2, class Difference2 \
+    >                                                                       \
+    prefix typename mpl::apply2<result_type,Derived1,Derived2>::type \
+    operator op(                                                            \
+        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)   \
+    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<             \
+        Derived1, Derived2                                              \
+      , typename mpl::apply2<result_type,Derived1,Derived2>::type       \
+    >::type                                                             \
+    operator op(                                                        \
+        iterator_facade<Derived1, V1, TC1, Reference1, Difference1> const& lhs   \
+      , iterator_facade<Derived2, V2, TC2, Reference2, Difference2> const& rhs)
+# endif 
+
+#  define BOOST_ITERATOR_FACADE_PLUS_HEAD(prefix,args)              \
+    template <class Derived, class V, class TC, class R, class D>   \
+    prefix Derived operator+ args
+
+  //
+  // Helper class for granting access to the iterator core interface.
+  //
+  // The simple core interface is used by iterator_facade. The core
+  // interface of a user/library defined iterator type should not be made public
+  // so that it does not clutter the public interface. Instead iterator_core_access
+  // should be made friend so that iterator_facade can access the core
+  // interface through iterator_core_access.
+  //
+  class iterator_core_access
+  {
+# if defined(BOOST_NO_MEMBER_TEMPLATE_FRIENDS)                  
+      // Tasteless as this may seem, making all members public allows member templates
+      // to work in the absence of member template friends.
+   public:
+# else
+      
+      template <class I, class V, class TC, class R, class D> friend class iterator_facade;
+
+#  define BOOST_ITERATOR_FACADE_RELATION(op)                                \
+      BOOST_ITERATOR_FACADE_INTEROP_HEAD(friend,op, boost::detail::always_bool2);
+
+      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(
+          friend, -, boost::detail::choose_difference_type)
+      ;
+
+      BOOST_ITERATOR_FACADE_PLUS_HEAD(
+          friend inline
+          , (iterator_facade<Derived, V, TC, R, D> const&
+           , typename Derived::difference_type)
+      )
+      ;
+
+      BOOST_ITERATOR_FACADE_PLUS_HEAD(
+          friend inline
+        , (typename Derived::difference_type
+           , iterator_facade<Derived, V, TC, R, D> const&)
+      )
+      ;
+
+# endif
+
+      template <class Facade>
+      static typename Facade::reference dereference(Facade const& f)
+      {
+          return f.dereference();
+      }
+
+      template <class Facade>
+      static void increment(Facade& f)
+      {
+          f.increment();
+      }
+
+      template <class Facade>
+      static void decrement(Facade& f)
+      {
+          f.decrement();
+      }
+
+      template <class Facade1, class Facade2>
+      static bool equal(Facade1 const& f1, Facade2 const& f2, mpl::true_)
+      {
+          return f1.equal(f2);
+      }
+
+      template <class Facade1, class Facade2>
+      static bool equal(Facade1 const& f1, Facade2 const& f2, mpl::false_)
+      {
+          return f2.equal(f1);
+      }
+
+      template <class Facade>
+      static void advance(Facade& f, typename Facade::difference_type n)
+      {
+          f.advance(n);
+      }
+
+      template <class Facade1, class Facade2>
+      static typename Facade1::difference_type distance_from(
+          Facade1 const& f1, Facade2 const& f2, mpl::true_)
+      {
+          return -f1.distance_to(f2);
+      }
+
+      template <class Facade1, class Facade2>
+      static typename Facade2::difference_type distance_from(
+          Facade1 const& f1, Facade2 const& f2, mpl::false_)
+      {
+          return f2.distance_to(f1);
+      }
+
+      //
+      // Curiously Recurring Template interface.
+      //
+      template <class I, class V, class TC, class R, class D>
+      static I& derived(iterator_facade<I,V,TC,R,D>& facade)
+      {
+          return *static_cast<I*>(&facade);
+      }
+
+      template <class I, class V, class TC, class R, class D>
+      static I const& derived(iterator_facade<I,V,TC,R,D> const& facade)
+      {
+          return *static_cast<I const*>(&facade);
+      }
+
+   private:
+      // objects of this class are useless
+      iterator_core_access(); //undefined
+  };
+
+  //
+  // 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
+# ifdef BOOST_ITERATOR_FACADE_NEEDS_ITERATOR_BASE
+    : public boost::detail::iterator_facade_types<
+         Value, CategoryOrTraversal, Reference, Difference
+      >::base
+#  undef BOOST_ITERATOR_FACADE_NEEDS_ITERATOR_BASE
+# endif
+  {
+   private:
+      //
+      // Curiously Recurring Template interface.
+      //
+      Derived& derived()
+      {
+          return *static_cast<Derived*>(this);
+      }
+
+      Derived const& derived() const
+      {
+          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_;
+      
+   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();
+      }
+
+# if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
+      typename boost::detail::postfix_increment_result<Derived,Value,Reference,CategoryOrTraversal>::type
+      operator++(int)
+      {
+          typename boost::detail::postfix_increment_result<Derived,Value,Reference,CategoryOrTraversal>::type
+          tmp(this->derived());
+          ++*this;
+          return tmp;
+      }
+# endif
+      
+      Derived& operator--()
+      {
+          iterator_core_access::decrement(this->derived());
+          return this->derived();
+      }
+
+      Derived operator--(int)
+      {
+          Derived tmp(this->derived());
+          --*this;
+          return tmp;
+      }
+
+      Derived& operator+=(difference_type n)
+      {
+          iterator_core_access::advance(this->derived(), n);
+          return this->derived();
+      }
+
+      Derived& operator-=(difference_type n)
+      {
+          iterator_core_access::advance(this->derived(), -n);
+          return this->derived();
+      }
+
+      Derived operator-(difference_type x) const
+      {
+          Derived result(this->derived());
+          return result -= x;
+      }
+
+# if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
+      // There appears to be a bug which trashes the data of classes
+      // derived from iterator_facade when they are assigned unless we
+      // define this assignment operator.  This bug is only revealed
+      // (so far) in STLPort debug mode, but it's clearly a codegen
+      // problem so we apply the workaround for all MSVC6.
+      iterator_facade& operator=(iterator_facade const&)
+      {
+          return *this;
+      }
+# endif
+  };
+
+# if !BOOST_WORKAROUND(BOOST_MSVC, < 1300)
+  template <class I, class V, class TC, class R, class D>
+  inline typename boost::detail::postfix_increment_result<I,V,R,TC>::type
+  operator++(
+      iterator_facade<I,V,TC,R,D>& i
+    , int
+  )
+  {
+      typename boost::detail::postfix_increment_result<I,V,R,TC>::type
+          tmp(*static_cast<I*>(&i));
+      
+      ++i;
+      
+      return tmp;
+  }
+# endif 
+
+  
+  //
+  // Comparison operator implementation. The library supplied operators
+  // enables the user to provide fully interoperable constant/mutable
+  // iterator types. I.e. the library provides all operators
+  // for all mutable/constant iterator combinations.
+  //
+  // Note though that this kind of interoperability for constant/mutable
+  // iterators is not required by the standard for container iterators.
+  // All the standard asks for is a conversion mutable -> constant.
+  // Most standard library implementations nowadays provide fully interoperable
+  // iterator implementations, but there are still heavily used implementations
+  // that do not provide them. (Actually it's even worse, they do not provide
+  // them for only a few iterators.)
+  //
+  // ?? Maybe a BOOST_ITERATOR_NO_FULL_INTEROPERABILITY macro should
+  //    enable the user to turn off mixed type operators
+  //
+  // The library takes care to provide only the right operator overloads.
+  // I.e.
+  //
+  // bool operator==(Iterator,      Iterator);
+  // bool operator==(ConstIterator, Iterator);
+  // bool operator==(Iterator,      ConstIterator);
+  // bool operator==(ConstIterator, ConstIterator);
+  //
+  //   ...
+  //
+  // In order to do so it uses c++ idioms that are not yet widely supported
+  // by current compiler releases. The library is designed to degrade gracefully
+  // in the face of compiler deficiencies. In general compiler
+  // deficiencies result in less strict error checking and more obscure
+  // error messages, functionality is not affected.
+  //
+  // For full operation compiler support for "Substitution Failure Is Not An Error"
+  // (aka. enable_if) and boost::is_convertible is required.
+  //
+  // The following problems occur if support is lacking.
+  //
+  // Pseudo code
+  //
+  // ---------------
+  // AdaptorA<Iterator1> a1;
+  // AdaptorA<Iterator2> a2;
+  //
+  // // This will result in a no such overload error in full operation
+  // // If enable_if or is_convertible is not supported
+  // // The instantiation will fail with an error hopefully indicating that
+  // // there is no operator== for Iterator1, Iterator2
+  // // The same will happen if no enable_if is used to remove
+  // // false overloads from the templated conversion constructor
+  // // of AdaptorA.
+  //
+  // a1 == a2;
+  // ----------------
+  //
+  // AdaptorA<Iterator> a;
+  // AdaptorB<Iterator> b;
+  //
+  // // This will result in a no such overload error in full operation
+  // // If enable_if is not supported the static assert used
+  // // in the operator implementation will fail.
+  // // This will accidently work if is_convertible is not supported.
+  //
+  // a == b;
+  // ----------------
+  //
+
+# ifdef BOOST_NO_ONE_WAY_ITERATOR_INTEROP
+#  define BOOST_ITERATOR_CONVERTIBLE(a,b) mpl::true_()
+# else
+#  define BOOST_ITERATOR_CONVERTIBLE(a,b) is_convertible<a,b>()
+# endif
+
+# define BOOST_ITERATOR_FACADE_INTEROP(op, result_type, return_prefix, base_op) \
+  BOOST_ITERATOR_FACADE_INTEROP_HEAD(inline, op, result_type)                   \
+  {                                                                             \
+      /* For those compilers that do not support enable_if */                   \
+      BOOST_STATIC_ASSERT((                                                     \
+          is_interoperable< Derived1, Derived2 >::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_RELATION(op, return_prefix, base_op) \
+  BOOST_ITERATOR_FACADE_INTEROP(                                    \
+      op                                                            \
+    , boost::detail::always_bool2                                   \
+    , return_prefix                                                 \
+    , base_op                                                       \
+  )
+
+  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
+
+  // operator- requires an additional part in the static assertion
+  BOOST_ITERATOR_FACADE_INTEROP(
+      -
+    , boost::detail::choose_difference_type
+    , return
+    , distance_from
+  )
+# undef BOOST_ITERATOR_FACADE_INTEROP
+# undef BOOST_ITERATOR_FACADE_INTEROP_HEAD
+
+# define BOOST_ITERATOR_FACADE_PLUS(args)           \
+  BOOST_ITERATOR_FACADE_PLUS_HEAD(inline, args)     \
+  {                                                 \
+      Derived tmp(static_cast<Derived const&>(i));  \
+      return tmp += n;                              \
+  }
+
+BOOST_ITERATOR_FACADE_PLUS((
+  iterator_facade<Derived, V, TC, R, D> const& i
+  , typename Derived::difference_type n
+))
+
+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
+
+} // namespace boost
+
+#include <boost/iterator/detail/config_undef.hpp>
+
+#endif // BOOST_ITERATOR_FACADE_23022003THW_HPP