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 Hu Chunming
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/*!
@file
Defines `boost::hana::negate`.
Copyright Louis Dionne 2013-2022
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_NEGATE_HPP
#define BOOST_HANA_NEGATE_HPP
#include <boost/hana/fwd/negate.hpp>
#include <boost/hana/concept/group.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/fwd/minus.hpp>
#include <boost/hana/zero.hpp>
#include <type_traits>
namespace boost { namespace hana {
//! @cond
template <typename X>
constexpr decltype(auto) negate_t::operator()(X&& x) const {
using G = typename hana::tag_of<X>::type;
using Negate = BOOST_HANA_DISPATCH_IF(negate_impl<G>,
hana::Group<G>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Group<G>::value,
"hana::negate(x) requires 'x' to be in a Group");
#endif
return Negate::apply(static_cast<X&&>(x));
}
//! @endcond
template <typename T, bool condition>
struct negate_impl<T, when<condition>> : default_ {
template <typename X>
static constexpr decltype(auto) apply(X&& x)
{ return hana::minus(hana::zero<T>(), static_cast<X&&>(x)); }
};
//////////////////////////////////////////////////////////////////////////
// Model for arithmetic data types
//////////////////////////////////////////////////////////////////////////
template <typename T>
struct negate_impl<T, when<std::is_arithmetic<T>::value &&
!std::is_same<bool, T>::value>> {
template <typename X>
static constexpr decltype(auto) apply(X&& x)
{ return -static_cast<X&&>(x); }
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_NEGATE_HPP
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