Isn't this giving the way for hard to find mistakes ?
Mistakes like what? The signature is specified when using the concept.
Well then one need to typedef the "final" concept or risk very strange errors if some type don't match, due to simple typo. I have tried something similar to this (shortened but I could provide a full version): ... BOOST_TYPE_ERASURE_MEMBER((connect_), Connect, 1); template <class Socket> struct disconnect { static void apply(Socket& sock) { sock.Disconnect(); } }; ... typedef mpl::vector<connect_<void(const EndPoint&)>, disconnect<_self>, copy_constructible<> > SockReqs; typedef any<mpl::vector<connect_<void(const EndPoint)> >, _self&> AnyConnect; // WOOPS, missed the "&" void DoConnect(AnyConnect ac) { ac.Connect(EndPoint()); } ... AnySockRef as2(...); AnyConnect ac2(as2); Even with clang I get 50 lines of errors starting with: clang++ -std=c++0x -c "/media/win/Projects/type_erasure/type_erasure/main.cpp" -O2 -Wall -o ./Release/main.o -I. -I/media/win/Projects/boost_trunk -I/media/win/Projects/type_erasure -I. In file included from /media/win/Projects/type_erasure/type_erasure/main.cpp:6: In file included from /media/win/Projects/type_erasure/boost/type_erasure/any.hpp:39: In file included from /media/win/Projects/type_erasure/boost/type_erasure/binding.hpp:29: In file included from /media/win/Projects/type_erasure/boost/type_erasure/detail/vtable.hpp:191: In file included from /media/win/Projects/boost_trunk/boost/preprocessor/iteration/detail/iter/forward1.hpp:52: /media/win/Projects/type_erasure/boost/type_erasure/detail/vtable.hpp:240:28: error: no matching member function for call to 'lookup' BOOST_PP_REPEAT(N, BOOST_TYPE_ERASURE_CONVERT_ELEMENT, ~) ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Julien