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|---|---|---|
| 7c673cae FG |
1 | /*! |
| 2 | @file | |
| 3 | Forward declares `boost::hana::mult`. | |
| 4 | ||
| 5 | @copyright Louis Dionne 2013-2016 | |
| 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 |