projects / ceph.git / blame
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|---|---|---|
| 7c673cae FG |
1 | /*! |
| 2 | @file | |
| 3 | Forward declares `boost::hana::drop_back`. | |
| 4 | ||
| 5 | @copyright Louis Dionne 2013-2016 | |
| 6 | Distributed under the Boost Software License, Version 1.0. | |
| 7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) | |
| 8 | */ | |
| 9 | ||
| 10 | #ifndef BOOST_HANA_FWD_DROP_BACK_HPP | |
| 11 | #define BOOST_HANA_FWD_DROP_BACK_HPP | |
| 12 | ||
| 13 | #include <boost/hana/config.hpp> | |
| 14 | #include <boost/hana/core/when.hpp> | |
| 15 | ||
| 16 | ||
| 17 | BOOST_HANA_NAMESPACE_BEGIN | |
| 18 | //! Drop the last `n` elements of a finite sequence, and return the rest. | |
| 19 | //! @ingroup group-Sequence | |
| 20 | //! | |
| 21 | //! Given a finite `Sequence` `xs` with a linearization of `[x1, ..., xm]` | |
| 22 | //! and a non-negative `IntegralConstant` `n`, `drop_back(xs, n)` is a | |
| 23 | //! sequence with the same tag as `xs` whose linearization is | |
| 24 | //! `[x1, ..., xm-n]`. If `n` is not given, it defaults to an | |
| 25 | //! `IntegralConstant` with a value equal to `1`. | |
| 26 | //! | |
| 27 | //! In case `length(xs) <= n`, `drop_back` will simply drop the whole | |
| 28 | //! sequence without failing, thus returning an empty sequence. | |
| 29 | //! | |
| 30 | //! | |
| 31 | //! @param xs | |
| 32 | //! The sequence from which elements are dropped. | |
| 33 | //! | |
| 34 | //! @param n | |
| 35 | //! A non-negative `IntegralConstant` representing the number of elements | |
| 36 | //! to be dropped from the end of the sequence. If `n` is not given, it | |
| 37 | //! defaults to an `IntegralConstant` with a value equal to `1`. | |
| 38 | //! | |
| 39 | //! | |
| 40 | //! Example | |
| 41 | //! ------- | |
| 42 | //! @include example/drop_back.cpp | |
| 43 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
| 44 | constexpr auto drop_back = [](auto&& xs[, auto const& n]) { | |
| 45 | return tag-dispatched; | |
| 46 | }; | |
| 47 | #else | |
| 48 | template <typename S, typename = void> | |
| 49 | struct drop_back_impl : drop_back_impl<S, when<true>> { }; | |
| 50 | ||
| 51 | struct drop_back_t { | |
| 52 | template <typename Xs, typename N> | |
| 53 | constexpr auto operator()(Xs&& xs, N const& n) const; | |
| 54 | ||
| 55 | template <typename Xs> | |
| 56 | constexpr auto operator()(Xs&& xs) const; | |
| 57 | }; | |
| 58 | ||
| 59 | constexpr drop_back_t drop_back{}; | |
| 60 | #endif | |
| 61 | BOOST_HANA_NAMESPACE_END | |
| 62 | ||
| 63 | #endif // !BOOST_HANA_FWD_DROP_BACK_HPP |