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1 | /*! |
2 | @file | |
3 | Forward declares `boost::hana::take_front` and `boost::hana::take_front_c`. | |
4 | ||
b32b8144 | 5 | @copyright Louis Dionne 2013-2017 |
7c673cae FG |
6 | Distributed 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_TAKE_FRONT_HPP | |
11 | #define BOOST_HANA_FWD_TAKE_FRONT_HPP | |
12 | ||
13 | #include <boost/hana/config.hpp> | |
14 | #include <boost/hana/core/when.hpp> | |
15 | ||
16 | #include <cstddef> | |
17 | ||
18 | ||
19 | BOOST_HANA_NAMESPACE_BEGIN | |
20 | //! Returns the first `n` elements of a sequence, or the whole sequence | |
21 | //! if the sequence has less than `n` elements. | |
22 | //! @ingroup group-Sequence | |
23 | //! | |
24 | //! Given a `Sequence` `xs` and an `IntegralConstant` `n`, `take_front(xs, n)` | |
25 | //! is a new sequence containing the first `n` elements of `xs`, in the | |
26 | //! same order. If `length(xs) <= n`, the whole sequence is returned and | |
27 | //! no error is triggered. | |
28 | //! | |
29 | //! | |
30 | //! @param xs | |
31 | //! The sequence to take the elements from. | |
32 | //! | |
33 | //! @param n | |
34 | //! A non-negative `IntegralConstant` representing the number of elements | |
35 | //! to keep in the resulting sequence. | |
36 | //! | |
37 | //! | |
38 | //! Example | |
39 | //! ------- | |
40 | //! @include example/take_front.cpp | |
41 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
42 | constexpr auto take_front = [](auto&& xs, auto const& n) { | |
43 | return tag-dispatched; | |
44 | }; | |
45 | #else | |
46 | template <typename S, typename = void> | |
47 | struct take_front_impl : take_front_impl<S, when<true>> { }; | |
48 | ||
49 | struct take_front_t { | |
50 | template <typename Xs, typename N> | |
51 | constexpr auto operator()(Xs&& xs, N const& n) const; | |
52 | }; | |
53 | ||
54 | constexpr take_front_t take_front{}; | |
55 | #endif | |
56 | ||
57 | //! Equivalent to `take_front`; provided for convenience. | |
58 | //! @ingroup group-Sequence | |
59 | //! | |
60 | //! | |
61 | //! Example | |
62 | //! ------- | |
63 | //! @include example/take_front_c.cpp | |
64 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
65 | template <std::size_t n> | |
66 | constexpr auto take_front_c = [](auto&& xs) { | |
67 | return hana::take_front(forwarded(xs), hana::size_c<n>); | |
68 | }; | |
69 | #else | |
70 | template <std::size_t n> | |
71 | struct take_front_c_t; | |
72 | ||
73 | template <std::size_t n> | |
74 | constexpr take_front_c_t<n> take_front_c{}; | |
75 | #endif | |
76 | BOOST_HANA_NAMESPACE_END | |
77 | ||
78 | #endif // !BOOST_HANA_FWD_TAKE_FRONT_HPP |