boost/hana/take_while.hpp

0001 /*!
0002 @file
0003 Defines `boost::hana::take_while`.
0004
0005 Copyright Louis Dionne 2013-2022
0006 Distributed under the Boost Software License, Version 1.0.
0007 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
0008  */
0009
0010 #ifndef BOOST_HANA_TAKE_WHILE_HPP
0011 #define BOOST_HANA_TAKE_WHILE_HPP
0012
0013 #include <boost/hana/fwd/take_while.hpp>
0014
0015 #include <boost/hana/concept/sequence.hpp>
0016 #include <boost/hana/config.hpp>
0017 #include <boost/hana/core/dispatch.hpp>
0018 #include <boost/hana/detail/first_unsatisfied_index.hpp>
0019 #include <boost/hana/take_front.hpp>
0020 #include <boost/hana/unpack.hpp>
0021
0022
0023 namespace boost { namespace hana {
0024     //! @cond
0025     template <typename Xs, typename Pred>
0026     constexpr auto take_while_t::operator()(Xs&& xs, Pred&& pred) const {
0027         using S = typename hana::tag_of<Xs>::type;
0028         using TakeWhile = BOOST_HANA_DISPATCH_IF(take_while_impl<S>,
0029             hana::Sequence<S>::value
0030         );
0031
0032     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
0033         static_assert(hana::Sequence<S>::value,
0034         "hana::take_while(xs, pred) requires 'xs' to be a Sequence");
0035     #endif
0036
0037         return TakeWhile::apply(static_cast<Xs&&>(xs),
0038                                 static_cast<Pred&&>(pred));
0039     }
0040     //! @endcond
0041
0042     template <typename S, bool condition>
0043     struct take_while_impl<S, when<condition>> : default_ {
0044         template <typename Xs, typename Pred>
0045         static constexpr auto apply(Xs&& xs, Pred&&) {
0046             using FirstUnsatisfied = decltype(
0047                 hana::unpack(static_cast<Xs&&>(xs),
0048                              detail::first_unsatisfied_index<Pred&&>{})
0049             );
0050             return hana::take_front(static_cast<Xs&&>(xs), FirstUnsatisfied{});
0051         }
0052     };
0053 }} // end namespace boost::hana
0054
0055 #endif // !BOOST_HANA_TAKE_WHILE_HPP