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Diffstat (limited to 'boost/hana/fwd/take_back.hpp')
| -rw-r--r-- | boost/hana/fwd/take_back.hpp | 58 |
1 files changed, 58 insertions, 0 deletions
diff --git a/boost/hana/fwd/take_back.hpp b/boost/hana/fwd/take_back.hpp new file mode 100644 index 0000000000..60560aa3d9 --- /dev/null +++ b/boost/hana/fwd/take_back.hpp @@ -0,0 +1,58 @@ +/*! +@file +Forward declares `boost::hana::take_back`. + +@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_FWD_TAKE_BACK_HPP +#define BOOST_HANA_FWD_TAKE_BACK_HPP + +#include <boost/hana/config.hpp> +#include <boost/hana/core/when.hpp> + +#include <cstddef> + + +BOOST_HANA_NAMESPACE_BEGIN + //! Returns the last `n` elements of a sequence, or the whole sequence + //! if the sequence has less than `n` elements. + //! @ingroup group-Sequence + //! + //! Given a `Sequence` `xs` and an `IntegralConstant` `n`, `take_back(xs, n)` + //! is a new sequence containing the last `n` elements of `xs`, in the + //! same order. If `length(xs) <= n`, the whole sequence is returned and + //! no error is triggered. + //! + //! + //! @param xs + //! The sequence to take the elements from. + //! + //! @param n + //! A non-negative `IntegralConstant` representing the number of elements + //! to keep in the resulting sequence. + //! + //! + //! Example + //! ------- + //! @include example/take_back.cpp +#ifdef BOOST_HANA_DOXYGEN_INVOKED + constexpr auto take_back = [](auto&& xs, auto const& n) { + return tag-dispatched; + }; +#else + template <typename S, typename = void> + struct take_back_impl : take_back_impl<S, when<true>> { }; + + struct take_back_t { + template <typename Xs, typename N> + constexpr auto operator()(Xs&& xs, N const& n) const; + }; + + constexpr take_back_t take_back{}; +#endif +BOOST_HANA_NAMESPACE_END + +#endif // !BOOST_HANA_FWD_TAKE_BACK_HPP |