/*! @file Defines `boost::hana::drop_while`. @copyright Louis Dionne 2013-2017 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_DROP_WHILE_HPP #define BOOST_HANA_DROP_WHILE_HPP #include <boost/hana/fwd/drop_while.hpp> #include <boost/hana/concept/foldable.hpp> #include <boost/hana/concept/iterable.hpp> #include <boost/hana/config.hpp> #include <boost/hana/core/dispatch.hpp> #include <boost/hana/detail/first_unsatisfied_index.hpp> #include <boost/hana/drop_front.hpp> #include <boost/hana/eval_if.hpp> #include <boost/hana/front.hpp> #include <boost/hana/is_empty.hpp> #include <boost/hana/lazy.hpp> BOOST_HANA_NAMESPACE_BEGIN //! @cond template <typename Xs, typename Pred> constexpr auto drop_while_t::operator()(Xs&& xs, Pred&& pred) const { using It = typename hana::tag_of<Xs>::type; using DropWhile = BOOST_HANA_DISPATCH_IF(drop_while_impl<It>, hana::Iterable<It>::value ); #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS static_assert(hana::Iterable<It>::value, "hana::drop_while(xs, pred) requires 'xs' to be an Iterable"); #endif return DropWhile::apply(static_cast<Xs&&>(xs), static_cast<Pred&&>(pred)); } //! @endcond namespace iterable_detail { struct drop_while_helper { struct next { template <typename Xs, typename Pred> constexpr decltype(auto) operator()(Xs&& xs, Pred&& pred) const { return hana::drop_while( hana::drop_front(static_cast<Xs&&>(xs)), static_cast<Pred&&>(pred) ); } }; template <typename Xs, typename Pred> constexpr decltype(auto) operator()(Xs&& xs, Pred&& pred) const { return hana::eval_if(pred(hana::front(xs)), hana::make_lazy(next{})(xs, pred), hana::make_lazy(xs) ); } }; } template <typename It, bool condition> struct drop_while_impl<It, when<condition>> : default_ { template <typename Xs, typename Pred> static constexpr auto apply(Xs&& xs, Pred&& pred) { return hana::eval_if(hana::is_empty(xs), hana::make_lazy(xs), hana::make_lazy(iterable_detail::drop_while_helper{})( xs, static_cast<Pred&&>(pred)) ); } }; template <typename S> struct drop_while_impl<S, when<hana::Foldable<S>::value>> { 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&&>{}) ); return hana::drop_front(static_cast<Xs&&>(xs), FirstUnsatisfied{}); } }; BOOST_HANA_NAMESPACE_END #endif // !BOOST_HANA_DROP_WHILE_HPP