mirror of
https://github.com/ecency/ecency-mobile.git
synced 2024-12-23 05:13:04 +03:00
54 lines
1.4 KiB
C++
54 lines
1.4 KiB
C++
/*!
|
|
@file
|
|
Defines `boost::hana::empty`.
|
|
|
|
@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_EMPTY_HPP
|
|
#define BOOST_HANA_EMPTY_HPP
|
|
|
|
#include <boost/hana/fwd/empty.hpp>
|
|
|
|
#include <boost/hana/concept/monad_plus.hpp>
|
|
#include <boost/hana/concept/sequence.hpp>
|
|
#include <boost/hana/config.hpp>
|
|
#include <boost/hana/core/dispatch.hpp>
|
|
#include <boost/hana/core/make.hpp>
|
|
|
|
|
|
BOOST_HANA_NAMESPACE_BEGIN
|
|
template <typename M>
|
|
struct empty_t {
|
|
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
|
|
static_assert(hana::MonadPlus<M>::value,
|
|
"hana::empty<M>() requires 'M' to be a MonadPlus");
|
|
#endif
|
|
|
|
constexpr auto operator()() const {
|
|
using Empty = BOOST_HANA_DISPATCH_IF(empty_impl<M>,
|
|
hana::MonadPlus<M>::value
|
|
);
|
|
|
|
return Empty::apply();
|
|
}
|
|
};
|
|
|
|
template <typename M, bool condition>
|
|
struct empty_impl<M, when<condition>> : default_ {
|
|
template <typename ...Args>
|
|
static constexpr auto apply(Args&& ...) = delete;
|
|
};
|
|
|
|
template <typename S>
|
|
struct empty_impl<S, when<Sequence<S>::value>> {
|
|
static constexpr auto apply() {
|
|
return hana::make<S>();
|
|
}
|
|
};
|
|
BOOST_HANA_NAMESPACE_END
|
|
|
|
#endif // !BOOST_HANA_EMPTY_HPP
|