v3/action/take.hpp

0001 /// \file
0002 // Range v3 library
0003 //
0004 //  Copyright Eric Niebler 2013-present
0005 //
0006 //  Use, modification and distribution is subject to the
0007 //  Boost Software License, Version 1.0. (See accompanying
0008 //  file LICENSE_1_0.txt or copy at
0009 //  http://www.boost.org/LICENSE_1_0.txt)
0010 //
0011 // Project home: https://github.com/ericniebler/range-v3
0012 //
0013
0014 #ifndef RANGES_V3_ACTION_TAKE_HPP
0015 #define RANGES_V3_ACTION_TAKE_HPP
0016
0017 #include <range/v3/range_fwd.hpp>
0018
0019 #include <range/v3/action/action.hpp>
0020 #include <range/v3/action/erase.hpp>
0021 #include <range/v3/functional/bind_back.hpp>
0022 #include <range/v3/iterator/concepts.hpp>
0023 #include <range/v3/iterator/operations.hpp>
0024 #include <range/v3/iterator/traits.hpp>
0025 #include <range/v3/utility/static_const.hpp>
0026
0027 #include <range/v3/detail/prologue.hpp>
0028
0029 namespace ranges
0030 {
0031     /// \addtogroup group-actions
0032     /// @{
0033     namespace actions
0034     {
0035         struct take_fn
0036         {
0037             template(typename Int)(
0038                 requires detail::integer_like_<Int>)
0039             constexpr auto operator()(Int n) const
0040             {
0041                 return make_action_closure(bind_back(take_fn{}, n));
0042             }
0043
0044             template(typename Rng)(
0045                 requires forward_range<Rng> AND
0046                     erasable_range<Rng &, iterator_t<Rng>, sentinel_t<Rng>>)
0047             Rng operator()(Rng && rng, range_difference_t<Rng> n) const
0048             {
0049                 RANGES_EXPECT(n >= 0);
0050                 ranges::actions::erase(
0051                     rng, ranges::next(begin(rng), n, end(rng)), end(rng));
0052                 return static_cast<Rng &&>(rng);
0053             }
0054         };
0055
0056         /// \relates actions::take_fn
0057         RANGES_INLINE_VARIABLE(take_fn, take)
0058     } // namespace actions
0059     /// @}
0060 } // namespace ranges
0061
0062 #include <range/v3/detail/epilogue.hpp>
0063
0064 #endif