Moved concept checks into a separate class, which makes MSVC better at dealing with them

[SVN r12255]

include/boost/iterator_adaptors.hpp

@@ -12,6 +12,9 @@
 //
 // Revision History:
 
+// 08 Jan 2001   David Abrahams
+//      Moved concept checks into a separate class, which makes MSVC
+//      better at dealing with them.
 // 07 Jan 2001   David Abrahams
 //      Choose proxy for operator->() only if the reference type is not a reference.
 //      Updated workarounds for __MWERKS__ == 0x2406
@@ -554,7 +557,7 @@ namespace detail {
   // An associative list is a list of key-value pairs. The list is
   // built out of cons_type's and is terminated by end_of_list.
 
-#if defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION) || defined(__BORLANDC__)
+# if defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION) || defined(__BORLANDC__)
   template <class AssocList, class Key>
   struct find_param;
 
@@ -583,7 +586,7 @@ namespace detail {
     typedef typename find_param_helper1<AssocList>::type select1;
     typedef typename select1::template select<AssocList, Key>::type type;
   };
-#else
+# else
   template <class AssocList, class Key> struct find_param;
 
   template <class Key>
@@ -600,7 +603,7 @@ namespace detail {
   struct find_param<detail::cons_type< detail::cons_type<Key1, Value>, Rest>, Key2> {
     typedef typename find_param<Rest, Key2>::type type;
   };
-#endif
+# endif
 
   struct make_named_arg {
     template <class Key, class Value>
@@ -617,26 +620,26 @@ namespace detail {
       enum { value = is_convertible<Value, named_template_param_base>::value };
   };
 
-#if defined(__MWERKS__) && __MWERKS__ <= 0x2406 // workaround for broken is_convertible implementation
+# if defined(__MWERKS__) && __MWERKS__ <= 0x2406 // workaround for broken is_convertible implementation
   template <class T> struct is_named_parameter<value_type_is<T> > { enum { value = true }; };
   template <class T> struct is_named_parameter<reference_is<T> > { enum { value = true }; };
   template <class T> struct is_named_parameter<pointer_is<T> > { enum { value = true }; };
   template <class T> struct is_named_parameter<difference_type_is<T> > { enum { value = true }; };
   template <class T> struct is_named_parameter<iterator_category_is<T> > { enum { value = true }; };
-#endif
+# endif
 
   template <class Key, class Value>
   struct make_arg {
-#ifdef __BORLANDC__
+# ifdef __BORLANDC__
     // Borland C++ doesn't like the extra indirection of is_named_parameter
     typedef typename
       if_true<(is_convertible<Value,named_template_param_base>::value)>::
       template then<make_named_arg, make_key_value>::type Make;
-#else
+# else
     enum { is_named = is_named_parameter<Value>::value };
     typedef typename if_true<(is_named)>::template
       then<make_named_arg, make_key_value>::type Make;
-#endif
+# endif
     typedef typename Make::template select<Key, Value>::type type;
   };
 
@@ -727,6 +730,29 @@ namespace detail {
       difference_type, pointer, reference> type;
   };
 
+  // This is really a partial concept check for iterators. Should it
+  // be moved or done differently?
+  template <class Category, class Value, class Difference, class Pointer, class Reference>
+  struct validator
+  {
+      BOOST_STATIC_CONSTANT(
+          bool, is_input_or_output_iter
+          = (boost::is_convertible<Category*,std::input_iterator_tag*>::value
+             | boost::is_convertible<Category*,std::output_iterator_tag*>::value));
+
+      // Iterators should satisfy one of the known categories
+      BOOST_STATIC_ASSERT(is_input_or_output_iter);
+
+      // Iterators >= ForwardIterator must produce real references
+      // as required by the C++ standard requirements in Table 74.
+      BOOST_STATIC_CONSTANT(
+          bool, forward_iter_with_real_reference
+          = ((!boost::is_convertible<Category*,std::forward_iterator_tag*>::value)
+             | boost::is_same<Reference,Value&>::value
+             | boost::is_same<Reference,typename add_const<Value>::type&>::value));
+
+      BOOST_STATIC_ASSERT(forward_iter_with_real_reference);
+  };
 } // namespace detail
 
 
@@ -738,8 +764,6 @@ namespace detail {
 #  define BOOST_ARG_DEPENDENT_TYPENAME
 # endif
 
-template <class T> struct undefined;
-
 //============================================================================
 //iterator_adaptor - Adapts a generic piece of data as an iterator. Adaptation
 //      is especially easy if the data being adapted is itself an iterator
@@ -800,25 +824,14 @@ struct iterator_adaptor :
     typedef Policies policies_type;
 
  private:
-    BOOST_STATIC_CONSTANT(bool, is_input_or_output_iter
+    typedef detail::validator<
-          = (boost::is_convertible<iterator_category*,std::input_iterator_tag*>::value
+        iterator_category,value_type,difference_type,pointer,reference
-             | boost::is_convertible<iterator_category*,std::output_iterator_tag*>::value));
+        > concept_check;
-
-    // Iterators should satisfy one of the known categories
-    BOOST_STATIC_ASSERT(is_input_or_output_iter);
-
-    // Iterators >= ForwardIterator must produce real references
-    // as required by the C++ standard requirements in Table 74.
-    BOOST_STATIC_CONSTANT(bool, forward_iter_with_real_reference
-                          = ((!boost::is_convertible<iterator_category*,std::forward_iterator_tag*>::value)
-                             | boost::is_same<reference,value_type&>::value
-                             | boost::is_same<reference,const value_type&>::value));
-    
-    // This check gives incorrect results in iter_traits_gen_test.cpp
-    BOOST_STATIC_ASSERT(forward_iter_with_real_reference);
 
  public:
-    iterator_adaptor() { }
+    iterator_adaptor()
+    {
+    }
 
     explicit
     iterator_adaptor(const Base& it, const Policies& p = Policies())