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0001 /*!
0002 @file
0003 Defines `boost::hana::negate`.
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_NEGATE_HPP
0011 #define BOOST_HANA_NEGATE_HPP
0012 
0013 #include <boost/hana/fwd/negate.hpp>
0014 
0015 #include <boost/hana/concept/group.hpp>
0016 #include <boost/hana/config.hpp>
0017 #include <boost/hana/core/dispatch.hpp>
0018 #include <boost/hana/fwd/minus.hpp>
0019 #include <boost/hana/zero.hpp>
0020 
0021 #include <type_traits>
0022 
0023 
0024 namespace boost { namespace hana {
0025     //! @cond
0026     template <typename X>
0027     constexpr decltype(auto) negate_t::operator()(X&& x) const {
0028         using G = typename hana::tag_of<X>::type;
0029         using Negate = BOOST_HANA_DISPATCH_IF(negate_impl<G>,
0030             hana::Group<G>::value
0031         );
0032 
0033     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
0034         static_assert(hana::Group<G>::value,
0035         "hana::negate(x) requires 'x' to be in a Group");
0036     #endif
0037 
0038         return Negate::apply(static_cast<X&&>(x));
0039     }
0040     //! @endcond
0041 
0042     template <typename T, bool condition>
0043     struct negate_impl<T, when<condition>> : default_ {
0044         template <typename X>
0045         static constexpr decltype(auto) apply(X&& x)
0046         { return hana::minus(hana::zero<T>(), static_cast<X&&>(x)); }
0047     };
0048 
0049     //////////////////////////////////////////////////////////////////////////
0050     // Model for arithmetic data types
0051     //////////////////////////////////////////////////////////////////////////
0052     template <typename T>
0053     struct negate_impl<T, when<std::is_arithmetic<T>::value &&
0054                                !std::is_same<bool, T>::value>> {
0055         template <typename X>
0056         static constexpr decltype(auto) apply(X&& x)
0057         { return -static_cast<X&&>(x); }
0058     };
0059 }} // end namespace boost::hana
0060 
0061 #endif // !BOOST_HANA_NEGATE_HPP