94 lines
3.2 KiB
C++
94 lines
3.2 KiB
C++
/*!
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@file
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Defines `boost::hana::drop_while`.
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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_DROP_WHILE_HPP
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#define BOOST_HANA_DROP_WHILE_HPP
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#include <boost/hana/fwd/drop_while.hpp>
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#include <boost/hana/concept/foldable.hpp>
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#include <boost/hana/concept/iterable.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/detail/first_unsatisfied_index.hpp>
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#include <boost/hana/drop_front.hpp>
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#include <boost/hana/eval_if.hpp>
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#include <boost/hana/front.hpp>
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#include <boost/hana/is_empty.hpp>
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#include <boost/hana/lazy.hpp>
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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 drop_while_t::operator()(Xs&& xs, Pred&& pred) const {
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using It = typename hana::tag_of<Xs>::type;
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using DropWhile = BOOST_HANA_DISPATCH_IF(drop_while_impl<It>,
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hana::Iterable<It>::value
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);
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#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
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static_assert(hana::Iterable<It>::value,
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"hana::drop_while(xs, pred) requires 'xs' to be an Iterable");
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#endif
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return DropWhile::apply(static_cast<Xs&&>(xs), static_cast<Pred&&>(pred));
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}
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//! @endcond
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namespace iterable_detail {
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struct drop_while_helper {
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struct next {
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template <typename Xs, typename Pred>
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constexpr decltype(auto) operator()(Xs&& xs, Pred&& pred) const {
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return hana::drop_while(
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hana::drop_front(static_cast<Xs&&>(xs)),
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static_cast<Pred&&>(pred)
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);
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}
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};
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template <typename Xs, typename Pred>
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constexpr decltype(auto) operator()(Xs&& xs, Pred&& pred) const {
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return hana::eval_if(pred(hana::front(xs)),
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hana::make_lazy(next{})(xs, pred),
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hana::make_lazy(xs)
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);
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}
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};
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}
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template <typename It, bool condition>
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struct drop_while_impl<It, when<condition>> : default_ {
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template <typename Xs, typename Pred>
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static constexpr auto apply(Xs&& xs, Pred&& pred) {
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return hana::eval_if(hana::is_empty(xs),
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hana::make_lazy(xs),
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hana::make_lazy(iterable_detail::drop_while_helper{})(
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xs, static_cast<Pred&&>(pred))
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);
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}
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};
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template <typename S>
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struct drop_while_impl<S, when<hana::Foldable<S>::value>> {
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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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return hana::drop_front(static_cast<Xs&&>(xs),
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FirstUnsatisfied{});
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_DROP_WHILE_HPP
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