changed how monoid identity element works

[SVN r8374]

include/boost/pending/concept_archetypes.hpp

@@ -36,6 +36,8 @@ namespace boost {
     friend void dummy_friend(); // just to avoid warnings
   };
 
+  // This is a helper class that provides a way to get a reference to
+  // an object.
   template <class T>
   class static_object {
   public:
@@ -104,8 +106,9 @@ namespace boost {
     default_archetype_base(detail::dummy_constructor x) { }
   };
 
-  // Careful, don't use same type for T and Base. That
-  // results in the conversion operator being invalid.
+  // Careful, don't use same type for T and Base. That results in the
+  // conversion operator being invalid.  Since T is often
+  // null_archetype, can't use null_archetype for Base.
   template <class T, class Base = default_archetype_base>
   class convertible_to_archetype : public Base {
   private:
@@ -295,8 +298,6 @@ namespace boost {
     return Return(dummy_cons); \
   }
 
-  // The default constructor used in Return() above is bad.
-
   BOOST_DEFINE_BINARY_OPERATOR_ARCHETYPE(+, plus_op)
   BOOST_DEFINE_BINARY_OPERATOR_ARCHETYPE(*, time_op)
   BOOST_DEFINE_BINARY_OPERATOR_ARCHETYPE(/, divide_op)

stl_concept_covering.cpp

@@ -109,13 +109,19 @@ namespace part_sum
 
 // for std::power
 
-template <class Base>
-boost::multipliable_archetype<Base>
-identity_element(std::multiplies< boost::multipliable_archetype<Base> >) {
-  return boost::multipliable_archetype<Base>(boost::dummy_cons);
+namespace power_stuff {
+  struct monoid_archetype {
+    monoid_archetype(boost::detail::dummy_constructor x) { }  
+  };
+  
+  boost::multipliable_archetype<monoid_archetype>
+  identity_element
+  (std::multiplies< boost::multipliable_archetype<monoid_archetype> >) 
+  {
+    return boost::multipliable_archetype<monoid_archetype>(boost::dummy_cons);
+  }
 }
 
-
 int
 main()
 {
@@ -1075,12 +1081,12 @@ main()
   // SGI STL extension
   {
     int n = 1;
-    multipliable_archetype<> x(dummy_cons);
+    multipliable_archetype<power_stuff::monoid_archetype> x(dummy_cons);
     x = std::power(x, n);
   }
   {
     int n = 1;
-    typedef multipliable_archetype<> T;
+    typedef multipliable_archetype<power_stuff::monoid_archetype> T;
     T x(dummy_cons);
     x = std::power(x, n, multiplies<T>());
   }