boost/hana/minus.hpp

0001 /*!
0002 @file
0003 Defines `boost::hana::minus`.
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_MINUS_HPP
0011 #define BOOST_HANA_MINUS_HPP
0012
0013 #include <boost/hana/fwd/minus.hpp>
0014
0015 #include <boost/hana/concept/constant.hpp>
0016 #include <boost/hana/concept/group.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 #include <boost/hana/fwd/negate.hpp>
0024 #include <boost/hana/plus.hpp>
0025 #include <boost/hana/value.hpp>
0026
0027 #include <type_traits>
0028
0029
0030 namespace boost { namespace hana {
0031     //! @cond
0032     template <typename X, typename Y>
0033     constexpr decltype(auto) minus_t::operator()(X&& x, Y&& y) const {
0034         using T = typename hana::tag_of<X>::type;
0035         using U = typename hana::tag_of<Y>::type;
0036         using Minus = BOOST_HANA_DISPATCH_IF(decltype(minus_impl<T, U>{}),
0037             hana::Group<T>::value &&
0038             hana::Group<U>::value
0039         );
0040
0041     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
0042         static_assert(hana::Group<T>::value,
0043         "hana::minus(x, y) requires 'x' to be in a Group");
0044
0045         static_assert(hana::Group<U>::value,
0046         "hana::minus(x, y) requires 'y' to be in a Group");
0047     #endif
0048
0049         return Minus::apply(static_cast<X&&>(x), static_cast<Y&&>(y));
0050     }
0051     //! @endcond
0052
0053     template <typename T, typename U, bool condition>
0054     struct minus_impl<T, U, when<condition>> : default_ {
0055         template <typename ...Args>
0056         static constexpr auto apply(Args&& ...) = delete;
0057     };
0058
0059     template <typename T, bool condition>
0060     struct minus_impl<T, T, when<condition>> : default_ {
0061         template <typename X, typename Y>
0062         static constexpr decltype(auto) apply(X&& x, Y&& y) {
0063             return hana::plus(static_cast<X&&>(x),
0064                               hana::negate(static_cast<Y&&>(y)));
0065         }
0066     };
0067
0068     // Cross-type overload
0069     template <typename T, typename U>
0070     struct minus_impl<T, U, when<
0071         detail::has_nontrivial_common_embedding<Group, T, U>::value
0072     >> {
0073         using C = typename common<T, U>::type;
0074         template <typename X, typename Y>
0075         static constexpr decltype(auto) apply(X&& x, Y&& y) {
0076             return hana::minus(hana::to<C>(static_cast<X&&>(x)),
0077                                hana::to<C>(static_cast<Y&&>(y)));
0078         }
0079     };
0080
0081     //////////////////////////////////////////////////////////////////////////
0082     // Model for arithmetic data types
0083     //////////////////////////////////////////////////////////////////////////
0084     template <typename T>
0085     struct minus_impl<T, T, when<std::is_arithmetic<T>::value &&
0086                                  !std::is_same<bool, T>::value>> {
0087         template <typename X, typename Y>
0088         static constexpr decltype(auto) apply(X&& x, Y&& y)
0089         { return static_cast<X&&>(x) - static_cast<Y&&>(y); }
0090     };
0091
0092     //////////////////////////////////////////////////////////////////////////
0093     // Model for Constants over a Group
0094     //////////////////////////////////////////////////////////////////////////
0095     namespace detail {
0096         template <typename C, typename X, typename Y>
0097         struct constant_from_minus {
0098             static constexpr auto value = hana::minus(hana::value<X>(), hana::value<Y>());
0099             using hana_tag = detail::CanonicalConstant<typename C::value_type>;
0100         };
0101     }
0102
0103     template <typename C>
0104     struct minus_impl<C, C, when<
0105         hana::Constant<C>::value &&
0106         Group<typename C::value_type>::value
0107     >> {
0108         template <typename X, typename Y>
0109         static constexpr decltype(auto) apply(X const&, Y const&)
0110         { return hana::to<C>(detail::constant_from_minus<C, X, Y>{}); }
0111     };
0112 }} // end namespace boost::hana
0113
0114 #endif // !BOOST_HANA_MINUS_HPP