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/*!
@file
Forward declares `boost::hana::drop_back`.
@copyright Louis Dionne 2013-2017
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_BACK_HPP
#define BOOST_HANA_FWD_DROP_BACK_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
BOOST_HANA_NAMESPACE_BEGIN
//! Drop the last `n` elements of a finite sequence, and return the rest.
//! @ingroup group-Sequence
//!
//! Given a finite `Sequence` `xs` with a linearization of `[x1, ..., xm]`
//! and a non-negative `IntegralConstant` `n`, `drop_back(xs, n)` is a
//! sequence with the same tag as `xs` whose linearization is
//! `[x1, ..., xm-n]`. If `n` is not given, it defaults to an
//! `IntegralConstant` with a value equal to `1`.
//!
//! In case `length(xs) <= n`, `drop_back` will simply drop the whole
//! sequence without failing, thus returning an empty sequence.
//!
//!
//! @param xs
//! The sequence from which elements are dropped.
//!
//! @param n
//! A non-negative `IntegralConstant` representing the number of elements
//! to be dropped from the end of the sequence. If `n` is not given, it
//! defaults to an `IntegralConstant` with a value equal to `1`.
//!
//!
//! Example
//! -------
//! @include example/drop_back.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto drop_back = [](auto&& xs[, auto const& n]) {
return tag-dispatched;
};
#else
template <typename S, typename = void>
struct drop_back_impl : drop_back_impl<S, when<true>> { };
struct drop_back_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_back_t drop_back{};
#endif
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_FWD_DROP_BACK_HPP
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