598bfd3f
 Hu Chunming
提交_GLIBCXX_USE_CX...
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/*!
@file
Defines `boost::hana::span`.
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_SPAN_HPP
#define BOOST_HANA_SPAN_HPP
#include <boost/hana/fwd/span.hpp>
#include <boost/hana/at.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/detail/nested_by.hpp> // required by fwd decl
#include <boost/hana/detail/first_unsatisfied_index.hpp>
#include <boost/hana/length.hpp>
#include <boost/hana/pair.hpp>
#include <boost/hana/unpack.hpp>
#include <cstddef>
#include <utility>
namespace boost { namespace hana {
//! @cond
template <typename Xs, typename Pred>
constexpr auto span_t::operator()(Xs&& xs, Pred&& pred) const {
using S = typename hana::tag_of<Xs>::type;
using Span = BOOST_HANA_DISPATCH_IF(span_impl<S>,
hana::Sequence<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Sequence<S>::value,
"hana::span(xs, pred) requires 'xs' to be a Sequence");
#endif
return Span::apply(static_cast<Xs&&>(xs), static_cast<Pred&&>(pred));
}
//! @endcond
template <typename S, bool condition>
struct span_impl<S, when<condition>> : default_ {
template <typename Xs, std::size_t ...before, std::size_t ...after>
static constexpr auto span_helper(Xs&& xs, std::index_sequence<before...>,
std::index_sequence<after...>)
{
return hana::make_pair(
hana::make<S>(hana::at_c<before>(static_cast<Xs&&>(xs))...),
hana::make<S>(hana::at_c<sizeof...(before) + after>(static_cast<Xs&&>(xs))...)
);
}
template <typename Xs, typename Pred>
static constexpr auto apply(Xs&& xs, Pred&&) {
using FirstUnsatisfied = decltype(
hana::unpack(static_cast<Xs&&>(xs),
detail::first_unsatisfied_index<Pred&&>{})
);
constexpr std::size_t breakpoint = FirstUnsatisfied::value;
constexpr std::size_t N = decltype(hana::length(xs))::value;
return span_helper(static_cast<Xs&&>(xs),
std::make_index_sequence<breakpoint>{},
std::make_index_sequence<N - breakpoint>{});
}
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_SPAN_HPP
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