title: Extension methods in c++
body: <p>I was searching for an implementation of extension methods in c++ and came upon <a href="http://groups.google.com/group/comp.std.c++/browse_thread/thread/c8b7234e249bc107">this comp.std.c++ discussion</a> which mentions that <code>polymorphic_map</code> can be used to associated methods with a class, but, the provided link seems to be dead.  Does anyone know what that answer was referring to, or if there is another way to extend classes in a similar manner to extension methods (perhaps through some usage of mixins?).  </p>
  
  <p>I know the canonical C++ solution is to use free functions; this is more out of curiosity than anything else.</p>