mirror of
https://github.com/ecency/ecency-mobile.git
synced 2024-12-23 21:35:04 +03:00
76 lines
2.5 KiB
C++
76 lines
2.5 KiB
C++
|
/*!
|
||
|
|
@file
|
||
|
|
Defines `boost::hana::take_front` and `boost::hana::take_front_c`.
|
||
|
|
|
||
|
|
@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_TAKE_FRONT_HPP
|
||
|
|
#define BOOST_HANA_TAKE_FRONT_HPP
|
||
|
|
|
||
|
|
#include <boost/hana/fwd/take_front.hpp>
|
||
|
|
|
||
|
|
#include <boost/hana/at.hpp>
|
||
|
|
#include <boost/hana/concept/integral_constant.hpp>
|
||
|
|
#include <boost/hana/concept/sequence.hpp>
|
||
|
|
#include <boost/hana/config.hpp>
|
||
|
|
#include <boost/hana/core/dispatch.hpp>
|
||
|
|
#include <boost/hana/core/make.hpp>
|
||
|
|
#include <boost/hana/integral_constant.hpp>
|
||
|
|
#include <boost/hana/length.hpp>
|
||
|
|
|
||
|
|
#include <cstddef>
|
||
|
|
#include <utility>
|
||
|
|
|
||
|
|
|
||
|
|
BOOST_HANA_NAMESPACE_BEGIN
|
||
|
|
//! @cond
|
||
|
|
template <typename Xs, typename N>
|
||
|
|
constexpr auto take_front_t::operator()(Xs&& xs, N const& n) const {
|
||
|
|
using S = typename hana::tag_of<Xs>::type;
|
||
|
|
using TakeFront = BOOST_HANA_DISPATCH_IF(take_front_impl<S>,
|
||
|
|
hana::Sequence<S>::value &&
|
||
|
|
hana::IntegralConstant<N>::value
|
||
|
|
);
|
||
|
|
|
||
|
|
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
|
||
|
|
static_assert(hana::Sequence<S>::value,
|
||
|
|
"hana::take_front(xs, n) requires 'xs' to be a Sequence");
|
||
|
|
|
||
|
|
static_assert(hana::IntegralConstant<N>::value,
|
||
|
|
"hana::take_front(xs, n) requires 'n' to be an IntegralConstant");
|
||
|
|
#endif
|
||
|
|
|
||
|
|
return TakeFront::apply(static_cast<Xs&&>(xs), n);
|
||
|
|
}
|
||
|
|
//! @endcond
|
||
|
|
|
||
|
|
template <typename S, bool condition>
|
||
|
|
struct take_front_impl<S, when<condition>> : default_ {
|
||
|
|
template <typename Xs, std::size_t ...n>
|
||
|
|
static constexpr auto take_front_helper(Xs&& xs, std::index_sequence<n...>) {
|
||
|
|
return hana::make<S>(hana::at_c<n>(static_cast<Xs&&>(xs))...);
|
||
|
|
}
|
||
|
|
|
||
|
|
template <typename Xs, typename N>
|
||
|
|
static constexpr auto apply(Xs&& xs, N const&) {
|
||
|
|
constexpr std::size_t n = N::value;
|
||
|
|
constexpr std::size_t size = decltype(hana::length(xs))::value;
|
||
|
|
return take_front_helper(static_cast<Xs&&>(xs),
|
||
|
|
std::make_index_sequence<(n < size ? n : size)>{});
|
||
|
|
}
|
||
|
|
};
|
||
|
|
|
||
|
|
template <std::size_t n>
|
||
|
|
struct take_front_c_t {
|
||
|
|
template <typename Xs>
|
||
|
|
constexpr auto operator()(Xs&& xs) const {
|
||
|
|
return hana::take_front(static_cast<Xs&&>(xs), hana::size_c<n>);
|
||
|
|
}
|
||
|
|
};
|
||
|
|
BOOST_HANA_NAMESPACE_END
|
||
|
|
|
||
|
|
#endif // !BOOST_HANA_TAKE_FRONT_HPP
|