boost/hana/remove_range.hpp

0001 /*!
0002 @file
0003 Defines `boost::hana::remove_range` and `boost::hana::remove_range_c`.
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_REMOVE_RANGE_HPP
0011 #define BOOST_HANA_REMOVE_RANGE_HPP
0012
0013 #include <boost/hana/fwd/remove_range.hpp>
0014
0015 #include <boost/hana/at.hpp>
0016 #include <boost/hana/concept/integral_constant.hpp>
0017 #include <boost/hana/concept/sequence.hpp>
0018 #include <boost/hana/config.hpp>
0019 #include <boost/hana/core/dispatch.hpp>
0020 #include <boost/hana/core/make.hpp>
0021 #include <boost/hana/integral_constant.hpp>
0022 #include <boost/hana/length.hpp>
0023
0024 #include <cstddef>
0025 #include <utility>
0026
0027
0028 namespace boost { namespace hana {
0029     //! @cond
0030     template <typename Xs, typename From, typename To>
0031     constexpr auto remove_range_t::operator()(Xs&& xs, From const& from, To const& to) const {
0032         using S = typename hana::tag_of<Xs>::type;
0033         using RemoveRange = BOOST_HANA_DISPATCH_IF(remove_range_impl<S>,
0034             hana::Sequence<S>::value &&
0035             hana::IntegralConstant<From>::value &&
0036             hana::IntegralConstant<To>::value
0037         );
0038
0039     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
0040         static_assert(hana::Sequence<S>::value,
0041         "hana::remove_range(xs, from, to) requires 'xs' to be a Sequence");
0042
0043         static_assert(hana::IntegralConstant<From>::value,
0044         "hana::remove_range(xs, from, to) requires 'from' to be an IntegralConstant");
0045
0046         static_assert(hana::IntegralConstant<To>::value,
0047         "hana::remove_range(xs, from, to) requires 'to' to be an IntegralConstant");
0048     #endif
0049
0050         return RemoveRange::apply(static_cast<Xs&&>(xs), from, to);
0051     }
0052     //! @endcond
0053
0054     template <typename S, bool condition>
0055     struct remove_range_impl<S, when<condition>> : default_ {
0056         template <std::size_t offset, typename Xs, std::size_t ...before, std::size_t ...after>
0057         static constexpr auto
0058         remove_range_helper(Xs&& xs, std::index_sequence<before...>,
0059                                      std::index_sequence<after...>)
0060         {
0061             return hana::make<S>(
0062                 hana::at_c<before>(static_cast<Xs&&>(xs))...,
0063                 hana::at_c<offset + after>(static_cast<Xs&&>(xs))...
0064             );
0065         }
0066
0067         template <typename Xs, typename From, typename To>
0068         static constexpr auto apply(Xs&& xs, From const&, To const&) {
0069             constexpr std::size_t from = From::value;
0070             constexpr std::size_t to = To::value;
0071             constexpr std::size_t len = decltype(hana::length(xs))::value;
0072             constexpr std::size_t before = from == to ? len : from;
0073             constexpr std::size_t after = from == to ? 0 : len - to;
0074
0075             static_assert(from <= to,
0076             "hana::remove_range(xs, from, to) requires '[from, to)' to be a "
0077             "valid interval, meaning that 'from <= to'");
0078             static_assert(from == to || from >= 0,
0079             "hana::remove_range(xs, from, to) requires 'from' to be non-negative");
0080             static_assert(from == to || to <= len,
0081             "hana::remove_range(xs, from, to) requires 'to <= length(xs)'");
0082
0083             return remove_range_helper<to>(static_cast<Xs&&>(xs),
0084                                            std::make_index_sequence<before>{},
0085                                            std::make_index_sequence<after>{});
0086         }
0087     };
0088
0089     template <std::size_t from, std::size_t to>
0090     struct remove_range_c_t {
0091         template <typename Xs>
0092         constexpr decltype(auto) operator()(Xs&& xs) const {
0093             return hana::remove_range(static_cast<Xs&&>(xs),
0094                                       hana::size_c<from>,
0095                                       hana::size_c<to>);
0096         }
0097     };
0098 }} // end namespace boost::hana
0099
0100 #endif // !BOOST_HANA_REMOVE_RANGE_HPP