"David B. Held" <dheld@codelogicconsulting.com> wrote in message news:cckhc5$m3l$1@sea.gmane.org...
The difference is that the component is called sp<>::nested<>. It's not called sp_nested<>, because they might want to typedef sp<> and instantiate the nested class over various types. By also exposing sp_nested<>, I'm asking them to call it by two different names depending on usage. It isn't totally evil, but it's less pleasant:
typedef sp<p1, p2> my_sp; my_sp::nested<foo> p; my_sp::nested<bar> q;
less<my_sp::nested<foo> > comp;
Got it. One last try -- a variation on Brian's: struct nested_base { }; template <class P1, class P2> struct sp { template <typename T> struct nested : nested_base { typedef P1 p1; typedef P1 p2; typedef T t; }; }; template <typename T, typename Enabler = void> struct less { }; template<typename T> struct enable_if_nested : boost::enable_if< boost::is_base_and_derived<nested_base, T> > { }; template <typename T> struct less< T, typename enable_if_nested<T>::type > { ... }; Jonathan