598bfd3f
 Hu Chunming
提交_GLIBCXX_USE_CX...
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/*!
@file
Defines `boost::hana::one`.
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_ONE_HPP
#define BOOST_HANA_ONE_HPP
#include <boost/hana/fwd/one.hpp>
#include <boost/hana/concept/constant.hpp>
#include <boost/hana/concept/ring.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/to.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/detail/canonical_constant.hpp>
#include <type_traits>
namespace boost { namespace hana {
//! @cond
template <typename R>
constexpr decltype(auto) one_t<R>::operator()() const {
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Ring<R>::value,
"hana::one<R>() requires 'R' to be a Ring");
#endif
using One = BOOST_HANA_DISPATCH_IF(one_impl<R>,
hana::Ring<R>::value
);
return One::apply();
}
//! @endcond
template <typename R, bool condition>
struct one_impl<R, when<condition>> : default_ {
template <typename ...Args>
static constexpr auto apply(Args&& ...) = delete;
};
//////////////////////////////////////////////////////////////////////////
// Model for non-boolean arithmetic data types
//////////////////////////////////////////////////////////////////////////
template <typename T>
struct one_impl<T, when<std::is_arithmetic<T>::value &&
!std::is_same<bool, T>::value>> {
static constexpr T apply()
{ return static_cast<T>(1); }
};
//////////////////////////////////////////////////////////////////////////
// Model for Constants over a Ring
//////////////////////////////////////////////////////////////////////////
namespace detail {
template <typename C>
struct constant_from_one {
static constexpr auto value = hana::one<typename C::value_type>();
using hana_tag = detail::CanonicalConstant<typename C::value_type>;
};
}
template <typename C>
struct one_impl<C, when<
hana::Constant<C>::value &&
Ring<typename C::value_type>::value
>> {
static constexpr decltype(auto) apply()
{ return hana::to<C>(detail::constant_from_one<C>{}); }
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_ONE_HPP
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