76 lines
2.6 KiB
C++
76 lines
2.6 KiB
C++
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/*!
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@file
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Defines `boost::hana::span`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_SPAN_HPP
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#define BOOST_HANA_SPAN_HPP
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#include <boost/hana/fwd/span.hpp>
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#include <boost/hana/at.hpp>
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#include <boost/hana/concept/sequence.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/dispatch.hpp>
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#include <boost/hana/core/make.hpp>
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#include <boost/hana/detail/nested_by.hpp> // required by fwd decl
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#include <boost/hana/detail/first_unsatisfied_index.hpp>
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#include <boost/hana/length.hpp>
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#include <boost/hana/pair.hpp>
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#include <boost/hana/unpack.hpp>
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#include <cstddef>
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#include <utility>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @cond
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template <typename Xs, typename Pred>
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constexpr auto span_t::operator()(Xs&& xs, Pred&& pred) const {
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using S = typename hana::tag_of<Xs>::type;
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using Span = BOOST_HANA_DISPATCH_IF(span_impl<S>,
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hana::Sequence<S>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Sequence<S>::value,
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"hana::span(xs, pred) requires 'xs' to be a Sequence");
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#endif
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return Span::apply(static_cast<Xs&&>(xs), static_cast<Pred&&>(pred));
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}
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//! @endcond
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template <typename S, bool condition>
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struct span_impl<S, when<condition>> : default_ {
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template <typename Xs, std::size_t ...before, std::size_t ...after>
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static constexpr auto span_helper(Xs&& xs, std::index_sequence<before...>,
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std::index_sequence<after...>)
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{
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return hana::make_pair(
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hana::make<S>(hana::at_c<before>(static_cast<Xs&&>(xs))...),
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hana::make<S>(hana::at_c<sizeof...(before) + after>(static_cast<Xs&&>(xs))...)
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);
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}
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template <typename Xs, typename Pred>
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static constexpr auto apply(Xs&& xs, Pred&&) {
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using FirstUnsatisfied = decltype(
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hana::unpack(static_cast<Xs&&>(xs),
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detail::first_unsatisfied_index<Pred&&>{})
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);
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constexpr std::size_t breakpoint = FirstUnsatisfied::value;
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constexpr std::size_t N = decltype(hana::length(xs))::value;
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return span_helper(static_cast<Xs&&>(xs),
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std::make_index_sequence<breakpoint>{},
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std::make_index_sequence<N - breakpoint>{});
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_SPAN_HPP
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