| 1 | /*! |
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| 2 | @file |
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| 3 | Forward declares `boost::hana::mult`. |
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| 4 | |
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| 5 | Copyright Louis Dionne 2013-2022 |
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| 6 | Distributed under the Boost Software License, Version 1.0. |
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| 7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) |
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| 8 | */ |
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| 9 | |
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| 10 | #ifndef BOOST_HANA_FWD_MULT_HPP |
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| 11 | #define BOOST_HANA_FWD_MULT_HPP |
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| 12 | |
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| 13 | #include <boost/hana/config.hpp> |
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| 14 | #include <boost/hana/core/when.hpp> |
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| 15 | |
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| 16 | |
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| 17 | namespace boost { namespace hana { |
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| 18 | //! Associative operation of a `Ring`. |
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| 19 | //! @ingroup group-Ring |
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| 20 | //! |
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| 21 | //! @param x, y |
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| 22 | //! Two `Ring` elements to combine with the `Ring` binary operation. |
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| 23 | //! |
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| 24 | //! |
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| 25 | //! Cross-type version of the method |
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| 26 | //! -------------------------------- |
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| 27 | //! The `mult` method is "overloaded" to handle distinct data types |
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| 28 | //! with certain properties. Specifically, `mult` is defined for |
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| 29 | //! _distinct_ data types `A` and `B` such that |
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| 30 | //! 1. `A` and `B` share a common data type `C`, as determined by the |
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| 31 | //! `common` metafunction |
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| 32 | //! 2. `A`, `B` and `C` are all `Ring`s when taken individually |
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| 33 | //! 3. `to<C> : A -> B` and `to<C> : B -> C` are `Ring`-embeddings, as |
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| 34 | //! determined by the `is_embedding` metafunction. |
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| 35 | //! |
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| 36 | //! The definition of `mult` for data types satisfying the above |
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| 37 | //! properties is obtained by setting |
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| 38 | //! @code |
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| 39 | //! mult(x, y) = mult(to<C>(x), to<C>(y)) |
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| 40 | //! @endcode |
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| 41 | //! |
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| 42 | //! |
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| 43 | //! Example |
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| 44 | //! ------- |
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| 45 | //! @include example/mult.cpp |
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| 46 | #ifdef BOOST_HANA_DOXYGEN_INVOKED |
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| 47 | constexpr auto mult = [](auto&& x, auto&& y) -> decltype(auto) { |
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| 48 | return tag-dispatched; |
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| 49 | }; |
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| 50 | #else |
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| 51 | template <typename T, typename U, typename = void> |
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| 52 | struct mult_impl : mult_impl<T, U, when<true>> { }; |
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| 53 | |
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| 54 | struct mult_t { |
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| 55 | template <typename X, typename Y> |
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| 56 | constexpr decltype(auto) operator()(X&& x, Y&& y) const; |
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| 57 | }; |
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| 58 | |
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| 59 | BOOST_HANA_INLINE_VARIABLE constexpr mult_t mult{}; |
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| 60 | #endif |
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| 61 | }} // end namespace boost::hana |
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| 62 | |
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| 63 | #endif // !BOOST_HANA_FWD_MULT_HPP |
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| 64 | |
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