Index: property_map.hpp
===================================================================
--- property_map.hpp	(revision 58237)
+++ property_map.hpp	(working copy)
@@ -302,7 +302,8 @@
     }
   };
 
-  struct identity_property_map;
+  template <typename T>
+  struct typed_identity_property_map;
 
   // A helper class for constructing a property map
   // from a class that implements operator[]
@@ -539,19 +540,23 @@
   };
 
   //=========================================================================
-  // A property map that applies the identity function to integers
-  struct identity_property_map
-    : public boost::put_get_helper<std::size_t, 
-        identity_property_map>
+  // A generalized identity property map
+  template <typename T>
+  struct typed_identity_property_map
+    : public boost::put_get_helper<T, typed_identity_property_map<T> >
   {
-    typedef std::size_t key_type;
-    typedef std::size_t value_type;
-    typedef std::size_t reference;
+    typedef T key_type;
+    typedef T value_type;
+    typedef T reference;
     typedef boost::readable_property_map_tag category;
 
     inline value_type operator[](const key_type& v) const { return v; }
   };
 
+//=========================================================================
+  // A property map that applies the identity function to integers
+  typedef typed_identity_property_map<std::size_t> identity_property_map;
+
   //=========================================================================
   // A property map that does not do anything, for
   // when you have to supply a property map, but don't need it.