diff options
Diffstat (limited to 'boost/hana/drop_while.hpp')
-rw-r--r-- | boost/hana/drop_while.hpp | 93 |
1 files changed, 93 insertions, 0 deletions
diff --git a/boost/hana/drop_while.hpp b/boost/hana/drop_while.hpp new file mode 100644 index 0000000000..53f58cf26a --- /dev/null +++ b/boost/hana/drop_while.hpp @@ -0,0 +1,93 @@ +/*! +@file +Defines `boost::hana::drop_while`. + +@copyright Louis Dionne 2013-2016 +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 |