--- On Thu, 11/13/08, Howard Hinnant wrote:
On Nov 13, 2008, at 3:55 PM, Beman Dawes wrote:
Howard would have to comment on that; I've pinged him to make him aware of this thread.
The Boost implementation can add extensions, and we can submit a comment on the CD. If it is as simple as a typedef, it stands a good chance of being accepted. If you write it up, with a proposed resolution, I'll submit it.
My only comment so far is that these look like good suggestions. A defect report should show a motivating code sample for best chances.
-Howard
Sections: 20.4.1 [Class template ratio], 20.4.2 [Arithmetic on ratio types] Discussion: Let's say that client code needs to use a unary metafunction named absolute_ratio in the following type definitions, to be evaluated lazily. // Usage. typedef std::ratio<-1,2> negative_one_half; typedef absolute_ratio<negative_one_half> one_half; typedef absolute_ratio< std::ratio_multiplies< one_half , negative_one_half > > one_fourth; // End usage. Assuming that a (partial) specialization of boost::mpl::negate exists for std::ratio, a programmer should be able to define absolute_ratio this way. template <typename R> struct absolute_ratio : boost::mpl::eval_if< R::type::num < 0 , boost::mpl::negate<R> , R > { }; The expression R::type::num is necessary because the std::ratio_multiplies metafunction is not required to inherit from std::ratio. However, the expression will not compile when it sees that std::ratio is not a metafunction. Proposed resolution: Add the nullary metafunction type definition to the ratio class template. namespace std { template <intmax_t N, intmax_t D = 1> class ratio { public: typedef ratio<N,D> type; static const intmax_t num; static const intmax_t den; }; } We should also require that each of the arithmetic metafunctions inherit from std::ratio if we want to allow the following usage (note the change from R::type::num to R::num). template <typename R> struct absolute_ratio : boost::mpl::eval_if< R::num < 0 , boost::mpl::negate<R> , R > { }; Cheers, Cromwell D. Enage