boost/hana/plus.hpp

0001 /*!
0002 @file
0003 Defines `boost::hana::plus`.
0004
0005 Copyright Louis Dionne 2013-2022
0006 Distributed under the Boost Software License, Version 1.0.
0007 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
0008  */
0009
0010 #ifndef BOOST_HANA_PLUS_HPP
0011 #define BOOST_HANA_PLUS_HPP
0012
0013 #include <boost/hana/fwd/plus.hpp>
0014
0015 #include <boost/hana/concept/constant.hpp>
0016 #include <boost/hana/concept/monoid.hpp>
0017 #include <boost/hana/config.hpp>
0018 #include <boost/hana/core/common.hpp>
0019 #include <boost/hana/core/to.hpp>
0020 #include <boost/hana/core/dispatch.hpp>
0021 #include <boost/hana/detail/canonical_constant.hpp>
0022 #include <boost/hana/detail/has_common_embedding.hpp>
0023
0024 #include <type_traits>
0025
0026
0027 namespace boost { namespace hana {
0028     //! @cond
0029     template <typename X, typename Y>
0030     constexpr decltype(auto) plus_t::operator()(X&& x, Y&& y) const {
0031         using T = typename hana::tag_of<X>::type;
0032         using U = typename hana::tag_of<Y>::type;
0033         using Plus = BOOST_HANA_DISPATCH_IF(decltype(plus_impl<T, U>{}),
0034             hana::Monoid<T>::value &&
0035             hana::Monoid<U>::value &&
0036             !is_default<plus_impl<T, U>>::value
0037         );
0038
0039     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
0040         static_assert(hana::Monoid<T>::value,
0041         "hana::plus(x, y) requires 'x' to be a Monoid");
0042
0043         static_assert(hana::Monoid<U>::value,
0044         "hana::plus(x, y) requires 'y' to be a Monoid");
0045
0046         static_assert(!is_default<plus_impl<T, U>>::value,
0047         "hana::plus(x, y) requires 'x' and 'y' to be embeddable "
0048         "in a common Monoid");
0049     #endif
0050
0051         return Plus::apply(static_cast<X&&>(x), static_cast<Y&&>(y));
0052     }
0053     //! @endcond
0054
0055     template <typename T, typename U, bool condition>
0056     struct plus_impl<T, U, when<condition>> : default_ {
0057         template <typename ...Args>
0058         static constexpr auto apply(Args&& ...) = delete;
0059     };
0060
0061     // Cross-type overload
0062     template <typename T, typename U>
0063     struct plus_impl<T, U, when<
0064         detail::has_nontrivial_common_embedding<Monoid, T, U>::value
0065     >> {
0066         using C = typename common<T, U>::type;
0067         template <typename X, typename Y>
0068         static constexpr decltype(auto) apply(X&& x, Y&& y) {
0069             return hana::plus(hana::to<C>(static_cast<X&&>(x)),
0070                               hana::to<C>(static_cast<Y&&>(y)));
0071         }
0072     };
0073
0074     //////////////////////////////////////////////////////////////////////////
0075     // Model for non-boolean arithmetic data types
0076     //////////////////////////////////////////////////////////////////////////
0077     template <typename T>
0078     struct plus_impl<T, T, when<
0079         std::is_arithmetic<T>::value &&
0080         !std::is_same<T, bool>::value
0081     >> {
0082         template <typename X, typename Y>
0083         static constexpr decltype(auto) apply(X&& x, Y&& y)
0084         { return static_cast<X&&>(x) + static_cast<Y&&>(y); }
0085     };
0086
0087     //////////////////////////////////////////////////////////////////////////
0088     // Model for Constants over a Monoid
0089     //////////////////////////////////////////////////////////////////////////
0090     namespace detail {
0091         template <typename C, typename X, typename Y>
0092         struct constant_from_plus {
0093             static constexpr auto value = hana::plus(hana::value<X>(), hana::value<Y>());
0094             using hana_tag = detail::CanonicalConstant<typename C::value_type>;
0095         };
0096     }
0097
0098     template <typename C>
0099     struct plus_impl<C, C, when<
0100         hana::Constant<C>::value &&
0101         Monoid<typename C::value_type>::value
0102     >> {
0103         template <typename X, typename Y>
0104         static constexpr decltype(auto) apply(X const&, Y const&)
0105         { return hana::to<C>(detail::constant_from_plus<C, X, Y>{}); }
0106     };
0107 }} // end namespace boost::hana
0108
0109 #endif // !BOOST_HANA_PLUS_HPP