[Boost-users] [proto] declaring result type for callable contexts

Eric, It seems like result types must be defined inside a struct eval, but examples in the documentation show the form commented out below. Is this a recent change? Also, in absence of a result_type declaration inside struct eval {...} the type defaults to int. Would it be possible to make it void or some_ugly_looking_type_that_tell_me_i_is_all_wrong? int might happen to be what the user wants, until he decide to change it and hides the problem. template<typename Expr> struct my_context : proto::callable_context<const my_context<Expr> > { struct eval {typedef double result_type;}; // doesn't work (anymore?) //typedef double result_type; };