72 lines
2.2 KiB
C++
72 lines
2.2 KiB
C++
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/*!
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@file
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Defines `boost::hana::unfold_left`.
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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_UNFOLD_LEFT_HPP
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#define BOOST_HANA_UNFOLD_LEFT_HPP
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#include <boost/hana/fwd/unfold_left.hpp>
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#include <boost/hana/append.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/empty.hpp>
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#include <boost/hana/first.hpp>
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#include <boost/hana/functional/partial.hpp>
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#include <boost/hana/optional.hpp>
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#include <boost/hana/second.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! @cond
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template <typename S>
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struct unfold_left_t {
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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::unfold_left<S> requires 'S' to be a Sequence");
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#endif
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template <typename State, typename F>
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constexpr auto operator()(State&& state, F&& f) const {
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return unfold_left_impl<S>::apply(
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static_cast<State&&>(state),
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static_cast<F&&>(f)
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);
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}
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};
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//! @endcond
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template <typename S, bool condition>
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struct unfold_left_impl<S, when<condition>> : default_ {
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struct unfold_left_helper {
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template <typename F, typename P>
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constexpr auto operator()(F&& f, P&& p) const {
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return hana::append(
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unfold_left_impl::apply(
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hana::first(static_cast<P&&>(p)),
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static_cast<F&&>(f)
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),
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hana::second(static_cast<P&&>(p))
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);
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}
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};
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template <typename Init, typename F>
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static constexpr auto apply(Init&& init, F&& f) {
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decltype(auto) elt = f(static_cast<Init&&>(init));
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return hana::maybe(empty<S>(),
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hana::partial(unfold_left_helper{}, static_cast<F&&>(f)),
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static_cast<decltype(elt)&&>(elt)
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);
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_UNFOLD_LEFT_HPP
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