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1 | /*! |
2 | @file | |
3 | Forward declares `boost::hana::slice` and `boost::hana::slice_c`. | |
4 | ||
b32b8144 | 5 | @copyright Louis Dionne 2013-2017 |
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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_SLICE_HPP | |
11 | #define BOOST_HANA_FWD_SLICE_HPP | |
12 | ||
13 | #include <boost/hana/config.hpp> | |
14 | #include <boost/hana/core/when.hpp> | |
15 | ||
16 | #include <cstddef> | |
17 | ||
18 | ||
1e59de90 | 19 | namespace boost { namespace hana { |
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20 | //! Extract the elements of a `Sequence` at the given indices. |
21 | //! @ingroup group-Sequence | |
22 | //! | |
23 | //! Given an arbitrary sequence of `indices`, `slice` returns a new | |
24 | //! sequence of the elements of the original sequence that appear at | |
25 | //! those indices. In other words, | |
26 | //! @code | |
27 | //! slice([x1, ..., xn], [i1, ..., ik]) == [x_i1, ..., x_ik] | |
28 | //! @endcode | |
29 | //! | |
30 | //! The indices do not have to be ordered or contiguous in any particular | |
31 | //! way, but they must not be out of the bounds of the sequence. It is | |
32 | //! also possible to specify the same index multiple times, in which case | |
33 | //! the element at this index will be repeatedly included in the resulting | |
34 | //! sequence. | |
35 | //! | |
36 | //! | |
37 | //! @param xs | |
38 | //! The sequence from which a subsequence is extracted. | |
39 | //! | |
40 | //! @param indices | |
41 | //! A compile-time `Foldable` containing non-negative `IntegralConstant`s | |
42 | //! representing the indices. The indices are 0-based, and they must all | |
43 | //! be in bounds of the `xs` sequence. Note that any `Foldable` will | |
44 | //! really do (no need for an `Iterable`, for example); the linearization | |
45 | //! of the `indices` is used to determine the order of the elements | |
46 | //! included in the slice. | |
47 | //! | |
48 | //! | |
49 | //! Example | |
50 | //! ------- | |
51 | //! @include example/slice.cpp | |
52 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
53 | constexpr auto slice = [](auto&& xs, auto&& indices) { | |
54 | return tag-dispatched; | |
55 | }; | |
56 | #else | |
57 | template <typename S, typename = void> | |
58 | struct slice_impl : slice_impl<S, when<true>> { }; | |
59 | ||
60 | struct slice_t { | |
61 | template <typename Xs, typename Indices> | |
62 | constexpr auto operator()(Xs&& xs, Indices&& indices) const; | |
63 | }; | |
64 | ||
1e59de90 | 65 | BOOST_HANA_INLINE_VARIABLE constexpr slice_t slice{}; |
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66 | #endif |
67 | ||
68 | //! Shorthand to `slice` a contiguous range of elements. | |
69 | //! @ingroup group-Sequence | |
70 | //! | |
71 | //! `slice_c` is simply a shorthand to slice a contiguous range of | |
72 | //! elements. In particular, `slice_c<from, to>(xs)` is equivalent to | |
73 | //! `slice(xs, range_c<std::size_t, from, to>)`, which simply slices | |
74 | //! all the elements of `xs` contained in the half-open interval | |
75 | //! delimited by `[from, to)`. Like for `slice`, the indices used with | |
76 | //! `slice_c` are 0-based and they must be in the bounds of the sequence | |
77 | //! being sliced. | |
78 | //! | |
79 | //! | |
80 | //! @tparam from | |
81 | //! The index of the first element in the slice. | |
82 | //! | |
83 | //! @tparam to | |
84 | //! One-past the index of the last element in the slice. It must hold | |
85 | //! that `from <= to`. | |
86 | //! | |
87 | //! | |
88 | //! Example | |
89 | //! ------- | |
90 | //! @include example/slice_c.cpp | |
91 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
92 | template <std::size_t from, std::size_t to> | |
93 | constexpr auto slice_c = [](auto&& xs) { | |
94 | return hana::slice(forwarded(xs), hana::range_c<std::size_t, from, to>); | |
95 | }; | |
96 | #else | |
97 | template <std::size_t from, std::size_t to> | |
98 | struct slice_c_t; | |
99 | ||
100 | template <std::size_t from, std::size_t to> | |
1e59de90 | 101 | BOOST_HANA_INLINE_VARIABLE constexpr slice_c_t<from, to> slice_c{}; |
7c673cae | 102 | #endif |
1e59de90 | 103 | }} // end namespace boost::hana |
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104 | |
105 | #endif // !BOOST_HANA_FWD_SLICE_HPP |