ceph/src/boost/boost/hana/fwd/slice.hpp

   1 /*!
   2 @file
   3 Forward declares `boost::hana::slice` and `boost::hana::slice_c`.
   4
   5 @copyright Louis Dionne 2013-2017
   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
  19 BOOST_HANA_NAMESPACE_BEGIN
  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
  65     constexpr slice_t slice{};
  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>
 101     constexpr slice_c_t<from, to> slice_c{};
 102 #endif
 103 BOOST_HANA_NAMESPACE_END
 104
 105 #endif // !BOOST_HANA_FWD_SLICE_HPP