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+/*!
+@file
+Forward declares `boost::hana::drop_front_exactly`.
+
+@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_DROP_FRONT_EXACTLY_HPP
+#define BOOST_HANA_FWD_DROP_FRONT_EXACTLY_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+ //! Drop the first `n` elements of an iterable, and return the rest.
+ //! @ingroup group-Iterable
+ //!
+ //! Given an `Iterable` `xs` with a linearization of `[x1, x2, ...]` and
+ //! a non-negative `IntegralConstant` `n`, `drop_front_exactly(xs, n)` is
+ //! an iterable with the same tag as `xs` whose linearization is
+ //! `[xn+1, xn+2, ...]`. In particular, note that this function does not
+ //! mutate the original iterable in any way. If `n` is not given, it
+ //! defaults to an `IntegralConstant` with a value equal to `1`.
+ //!
+ //! It is an error to use `drop_front_exactly` with `n > length(xs)`. This
+ //! additional guarantee allows `drop_front_exactly` to be better optimized
+ //! than the `drop_front` function, which allows `n > length(xs)`.
+ //!
+ //!
+ //! @param xs
+ //! The iterable from which elements are dropped.
+ //!
+ //! @param n
+ //! A non-negative `IntegralConstant` representing the number of elements
+ //! to be dropped from the iterable. In addition to being non-negative,
+ //! `n` must be less than or equal to the number of elements in `xs`.
+ //! If `n` is not given, it defaults to an `IntegralConstant` with a value
+ //! equal to `1`.
+ //!
+ //!
+ //! Example
+ //! -------
+ //! @include example/drop_front_exactly.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+ constexpr auto drop_front_exactly = [](auto&& xs[, auto const& n]) {
+ return tag-dispatched;
+ };
+#else
+ template <typename It, typename = void>
+ struct drop_front_exactly_impl : drop_front_exactly_impl<It, when<true>> { };
+
+ struct drop_front_exactly_t {
+ template <typename Xs, typename N>
+ constexpr auto operator()(Xs&& xs, N const& n) const;
+
+ template <typename Xs>
+ constexpr auto operator()(Xs&& xs) const;
+ };
+
+ constexpr drop_front_exactly_t drop_front_exactly{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_DROP_FRONT_EXACTLY_HPP