1/*!
2@file
3Forward declares `boost::hana::drop_front`.
4
5Copyright Louis Dionne 2013-2022
6Distributed 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_FRONT_HPP
11#define BOOST_HANA_FWD_DROP_FRONT_HPP
12
13#include <boost/hana/config.hpp>
14#include <boost/hana/core/when.hpp>
15
16
17namespace boost { namespace hana {
18 //! Drop the first `n` elements of an iterable, and return the rest.
19 //! @ingroup group-Iterable
20 //!
21 //! Given an `Iterable` `xs` with a linearization of `[x1, x2, ...]` and
22 //! a non-negative `IntegralConstant` `n`, `drop_front(xs, n)` is an
23 //! iterable with the same tag as `xs` whose linearization is
24 //! `[xn+1, xn+2, ...]`. In particular, note that this function does not
25 //! mutate the original iterable in any way. If `n` is not given, it
26 //! defaults to an `IntegralConstant` with a value equal to `1`.
27 //!
28 //! In case `length(xs) <= n`, `drop_front` will simply drop the whole
29 //! iterable without failing, thus returning an empty iterable. This is
30 //! different from `drop_front_exactly`, which expects `n <= length(xs)`
31 //! but can be better optimized because of this additional guarantee.
32 //!
33 //!
34 //! @param xs
35 //! The iterable from which elements are dropped.
36 //!
37 //! @param n
38 //! A non-negative `IntegralConstant` representing the number of elements
39 //! to be dropped from the iterable. If `n` is not given, it defaults to
40 //! an `IntegralConstant` with a value equal to `1`.
41 //!
42 //!
43 //! Example
44 //! -------
45 //! @include example/drop_front.cpp
46#ifdef BOOST_HANA_DOXYGEN_INVOKED
47 constexpr auto drop_front = [](auto&& xs[, auto const& n]) {
48 return tag-dispatched;
49 };
50#else
51 template <typename It, typename = void>
52 struct drop_front_impl : drop_front_impl<It, when<true>> { };
53
54 struct drop_front_t {
55 template <typename Xs, typename N>
56 constexpr auto operator()(Xs&& xs, N const& n) const;
57
58 template <typename Xs>
59 constexpr auto operator()(Xs&& xs) const;
60 };
61
62 BOOST_HANA_INLINE_VARIABLE constexpr drop_front_t drop_front{};
63#endif
64}} // end namespace boost::hana
65
66#endif // !BOOST_HANA_FWD_DROP_FRONT_HPP
67

source code of boost/libs/hana/include/boost/hana/fwd/drop_front.hpp