1 /*! 2 @file 3 Forward declares `boost::hana::mult`. 4 5 @copyright Louis Dionne 2013-2017 6 Distributed under the Boost Software License, Version 1.0. 7 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) 8 */ 9 10 #ifndef BOOST_HANA_FWD_MULT_HPP 11 #define BOOST_HANA_FWD_MULT_HPP 12 13 #include <boost/hana/config.hpp> 14 #include <boost/hana/core/when.hpp> 15 16 17 BOOST_HANA_NAMESPACE_BEGIN 18 //! Associative operation of a `Ring`. 19 //! @ingroup group-Ring 20 //! 21 //! @param x, y 22 //! Two `Ring` elements to combine with the `Ring` binary operation. 23 //! 24 //! 25 //! Cross-type version of the method 26 //! -------------------------------- 27 //! The `mult` method is "overloaded" to handle distinct data types 28 //! with certain properties. Specifically, `mult` is defined for 29 //! _distinct_ data types `A` and `B` such that 30 //! 1. `A` and `B` share a common data type `C`, as determined by the 31 //! `common` metafunction 32 //! 2. `A`, `B` and `C` are all `Ring`s when taken individually 33 //! 3. `to<C> : A -> B` and `to<C> : B -> C` are `Ring`-embeddings, as 34 //! determined by the `is_embedding` metafunction. 35 //! 36 //! The definition of `mult` for data types satisfying the above 37 //! properties is obtained by setting 38 //! @code 39 //! mult(x, y) = mult(to<C>(x), to<C>(y)) 40 //! @endcode 41 //! 42 //! 43 //! Example 44 //! ------- 45 //! @include example/mult.cpp 46 #ifdef BOOST_HANA_DOXYGEN_INVOKED 47 constexpr auto mult = [](auto&& x, auto&& y) -> decltype(auto) { 48 return tag-dispatched; 49 }; 50 #else 51 template <typename T, typename U, typename = void> 52 struct mult_impl : mult_impl<T, U, when<true>> { }; 53 54 struct mult_t { 55 template <typename X, typename Y> 56 constexpr decltype(auto) operator()(X&& x, Y&& y) const; 57 }; 58 59 constexpr mult_t mult{}; 60 #endif 61 BOOST_HANA_NAMESPACE_END 62 63 #endif // !BOOST_HANA_FWD_MULT_HPP 64