67 lines
2.3 KiB
C++
67 lines
2.3 KiB
C++
/*!
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@file
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Forward declares `boost::hana::drop_front`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_FWD_DROP_FRONT_HPP
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#define BOOST_HANA_FWD_DROP_FRONT_HPP
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/when.hpp>
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BOOST_HANA_NAMESPACE_BEGIN
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//! Drop the first `n` elements of an iterable, and return the rest.
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//! @ingroup group-Iterable
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//!
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//! Given an `Iterable` `xs` with a linearization of `[x1, x2, ...]` and
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//! a non-negative `IntegralConstant` `n`, `drop_front(xs, n)` is an
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//! iterable with the same tag as `xs` whose linearization is
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//! `[xn+1, xn+2, ...]`. In particular, note that this function does not
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//! mutate the original iterable in any way. If `n` is not given, it
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//! defaults to an `IntegralConstant` with a value equal to `1`.
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//!
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//! In case `length(xs) <= n`, `drop_front` will simply drop the whole
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//! iterable without failing, thus returning an empty iterable. This is
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//! different from `drop_front_exactly`, which expects `n <= length(xs)`
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//! but can be better optimized because of this additional guarantee.
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//!
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//!
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//! @param xs
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//! The iterable from which elements are dropped.
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//!
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//! @param n
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//! A non-negative `IntegralConstant` representing the number of elements
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//! to be dropped from the iterable. If `n` is not given, it defaults to
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//! an `IntegralConstant` with a value equal to `1`.
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//!
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//!
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//! Example
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//! -------
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//! @include example/drop_front.cpp
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#ifdef BOOST_HANA_DOXYGEN_INVOKED
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constexpr auto drop_front = [](auto&& xs[, auto const& n]) {
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return tag-dispatched;
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};
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#else
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template <typename It, typename = void>
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struct drop_front_impl : drop_front_impl<It, when<true>> { };
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struct drop_front_t {
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template <typename Xs, typename N>
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constexpr auto operator()(Xs&& xs, N const& n) const;
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template <typename Xs>
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constexpr auto operator()(Xs&& xs) const;
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};
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constexpr drop_front_t drop_front{};
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#endif
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_FWD_DROP_FRONT_HPP
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