mirror of
https://github.com/ecency/ecency-mobile.git
synced 2024-12-23 13:22:02 +03:00
82 lines
2.5 KiB
C++
82 lines
2.5 KiB
C++
/*!
|
|
@file
|
|
Defines `boost::hana::zero`.
|
|
|
|
@copyright Louis Dionne 2013-2016
|
|
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_ZERO_HPP
|
|
#define BOOST_HANA_ZERO_HPP
|
|
|
|
#include <boost/hana/fwd/zero.hpp>
|
|
|
|
#include <boost/hana/concept/constant.hpp>
|
|
#include <boost/hana/concept/monoid.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>
|
|
|
|
|
|
BOOST_HANA_NAMESPACE_BEGIN
|
|
template <typename M>
|
|
struct zero_t {
|
|
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
|
|
static_assert(hana::Monoid<M>::value,
|
|
"hana::zero<M>() requires 'M' to be a Monoid");
|
|
#endif
|
|
|
|
constexpr decltype(auto) operator()() const {
|
|
using Zero = BOOST_HANA_DISPATCH_IF(zero_impl<M>,
|
|
hana::Monoid<M>::value
|
|
);
|
|
|
|
return Zero::apply();
|
|
}
|
|
};
|
|
|
|
template <typename M, bool condition>
|
|
struct zero_impl<M, when<condition>> : default_ {
|
|
template <typename ...Args>
|
|
static constexpr auto apply(Args&& ...) = delete;
|
|
};
|
|
|
|
//////////////////////////////////////////////////////////////////////////
|
|
// Model for non-boolean arithmetic data types
|
|
//////////////////////////////////////////////////////////////////////////
|
|
template <typename T>
|
|
struct zero_impl<T, when<
|
|
std::is_arithmetic<T>::value &&
|
|
!std::is_same<T, bool>::value
|
|
>> {
|
|
static constexpr T apply()
|
|
{ return static_cast<T>(0); }
|
|
};
|
|
|
|
//////////////////////////////////////////////////////////////////////////
|
|
// Model for Constants over a Monoid
|
|
//////////////////////////////////////////////////////////////////////////
|
|
namespace detail {
|
|
template <typename C>
|
|
struct constant_from_zero {
|
|
static constexpr auto value = hana::zero<typename C::value_type>();
|
|
using hana_tag = detail::CanonicalConstant<typename C::value_type>;
|
|
};
|
|
}
|
|
|
|
template <typename C>
|
|
struct zero_impl<C, when<
|
|
hana::Constant<C>::value &&
|
|
Monoid<typename C::value_type>::value
|
|
>> {
|
|
static constexpr decltype(auto) apply()
|
|
{ return hana::to<C>(detail::constant_from_zero<C>{}); }
|
|
};
|
|
BOOST_HANA_NAMESPACE_END
|
|
|
|
#endif // !BOOST_HANA_ZERO_HPP
|