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/*! @file Forward declares `boost::hana::mult`. @copyright Louis Dionne 2013-2017 Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) */ #ifndef BOOST_HANA_FWD_MULT_HPP #define BOOST_HANA_FWD_MULT_HPP #include <boost/hana/config.hpp> #include <boost/hana/core/when.hpp> BOOST_HANA_NAMESPACE_BEGIN //! Associative operation of a `Ring`. //! @ingroup group-Ring //! //! @param x, y //! Two `Ring` elements to combine with the `Ring` binary operation. //! //! //! Cross-type version of the method //! -------------------------------- //! The `mult` method is "overloaded" to handle distinct data types //! with certain properties. Specifically, `mult` is defined for //! _distinct_ data types `A` and `B` such that //! 1. `A` and `B` share a common data type `C`, as determined by the //! `common` metafunction //! 2. `A`, `B` and `C` are all `Ring`s when taken individually //! 3. `to<C> : A -> B` and `to<C> : B -> C` are `Ring`-embeddings, as //! determined by the `is_embedding` metafunction. //! //! The definition of `mult` for data types satisfying the above //! properties is obtained by setting //! @code //! mult(x, y) = mult(to<C>(x), to<C>(y)) //! @endcode //! //! //! Example //! ------- //! @include example/mult.cpp #ifdef BOOST_HANA_DOXYGEN_INVOKED constexpr auto mult = [](auto&& x, auto&& y) -> decltype(auto) { return tag-dispatched; }; #else template <typename T, typename U, typename = void> struct mult_impl : mult_impl<T, U, when<true>> { }; struct mult_t { template <typename X, typename Y> constexpr decltype(auto) operator()(X&& x, Y&& y) const; }; constexpr mult_t mult{}; #endif BOOST_HANA_NAMESPACE_END #endif // !BOOST_HANA_FWD_MULT_HPP