Edit: /usr/include/boost/hana/zero.hpp (2454B)
/*!
@file
Defines `boost::hana::zero`.
@copyright Louis Dionne 2013-2017
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
#include
#include
#include
#include
#include
#include
#include
BOOST_HANA_NAMESPACE_BEGIN
//! @cond
template
constexpr decltype(auto) zero_t::operator()() const {
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Monoid::value,
"hana::zero() requires 'M' to be a Monoid");
#endif
using Zero = BOOST_HANA_DISPATCH_IF(zero_impl,
hana::Monoid::value
);
return Zero::apply();
}
//! @endcond
template
struct zero_impl> : default_ {
template
static constexpr auto apply(Args&& ...) = delete;
};
//////////////////////////////////////////////////////////////////////////
// Model for non-boolean arithmetic data types
//////////////////////////////////////////////////////////////////////////
template
struct zero_impl::value &&
!std::is_same::value
>> {
static constexpr T apply()
{ return static_cast(0); }
};
//////////////////////////////////////////////////////////////////////////
// Model for Constants over a Monoid
//////////////////////////////////////////////////////////////////////////
namespace detail {
template
struct constant_from_zero {
static constexpr auto value = hana::zero();
using hana_tag = detail::CanonicalConstant;
};
}
template
struct zero_impl::value &&
Monoid::value
>> {
static constexpr decltype(auto) apply()
{ return hana::to(detail::constant_from_zero{}); }
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_ZERO_HPP