[Boost-users] [Container] ptr_set with user define compare function

I've defined a function object as below: struct BaseAddrLess : public std::binary_function { result_type operator() (const first_argument_type& lhs, const second_argument_type& rhs) const { return &lhs < &rhs; } }; and use as a compare function in ptr_set like this: ptr_set bset; when the class Base is a abstract class the vc9 compiler will complain use of undefined type 'boost::result_of<F>' What causes this problem? How to solve it? Thank you for your patience to read my poor english. S.C. Leung