ceph/src/boost/libs/hana/include/boost/hana/ext/std/integer_sequence.hpp

   1 /*!
   2 @file
   3 Adapts `std::integer_sequence` for use with Hana.
   4
   5 @copyright Louis Dionne 2013-2016
   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_EXT_STD_INTEGER_SEQUENCE_HPP
  11 #define BOOST_HANA_EXT_STD_INTEGER_SEQUENCE_HPP
  12
  13 #include <boost/hana/bool.hpp>
  14 #include <boost/hana/config.hpp>
  15 #include <boost/hana/detail/fast_and.hpp>
  16 #include <boost/hana/ext/std/integral_constant.hpp>
  17 #include <boost/hana/fwd/at.hpp>
  18 #include <boost/hana/fwd/core/tag_of.hpp>
  19 #include <boost/hana/fwd/drop_front.hpp>
  20 #include <boost/hana/fwd/equal.hpp>
  21 #include <boost/hana/fwd/is_empty.hpp>
  22 #include <boost/hana/fwd/unpack.hpp>
  23
  24 #include <cstddef>
  25 #include <type_traits>
  26 #include <utility>
  27
  28
  29 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  30 namespace std {
  31     //! @ingroup group-ext-std
  32     //! Adaptation of `std::integer_sequence` for Hana.
  33     //!
  34     //!
  35     //!
  36     //! Modeled concepts
  37     //! ----------------
  38     //! 1. `Comparable`\n
  39     //! Two `std::integer_sequence`s are equal if and only if they have the
  40     //! same number of elements, and if corresponding elements compare equal.
  41     //! The types of the elements held in both `integer_sequence`s may be
  42     //! different, as long as they can be compared.
  43     //! @include example/ext/std/integer_sequence/comparable.cpp
  44     //!
  45     //! 2. `Foldable`\n
  46     //! Folding an `integer_sequence` is equivalent to folding a sequence of
  47     //! `std::integral_constant`s with the corresponding types.
  48     //! @include example/ext/std/integer_sequence/foldable.cpp
  49     //!
  50     //! 3. `Iterable`\n
  51     //! Iterating over an `integer_sequence` is equivalent to iterating over
  52     //! a sequence of the corresponding `std::integral_constant`s.
  53     //! @include example/ext/std/integer_sequence/iterable.cpp
  54     //!
  55     //! 4. `Searchable`\n
  56     //! Searching through an `integer_sequence` is equivalent to searching
  57     //! through the corresponding sequence of `std::integral_constant`s.
  58     //! @include example/ext/std/integer_sequence/searchable.cpp
  59     template <typename T, T ...v>
  60     struct integer_sequence { };
  61 }
  62 #endif
  63
  64
  65 BOOST_HANA_NAMESPACE_BEGIN
  66     namespace ext { namespace std { struct integer_sequence_tag; }}
  67
  68     template <typename T, T ...v>
  69     struct tag_of<std::integer_sequence<T, v...>> {
  70         using type = ext::std::integer_sequence_tag;
  71     };
  72
  73     //////////////////////////////////////////////////////////////////////////
  74     // Comparable
  75     //////////////////////////////////////////////////////////////////////////
  76     template <>
  77     struct equal_impl<ext::std::integer_sequence_tag, ext::std::integer_sequence_tag> {
  78         template <typename X, X ...xs, typename Y, Y ...ys>
  79         static constexpr hana::bool_<detail::fast_and<(xs == ys)...>::value>
  80         apply(std::integer_sequence<X, xs...> const&, std::integer_sequence<Y, ys...> const&)
  81         { return {}; }
  82
  83         template <typename Xs, typename Ys>
  84         static constexpr hana::false_ apply(Xs const&, Ys const&, ...)
  85         { return {}; }
  86     };
  87
  88     //////////////////////////////////////////////////////////////////////////
  89     // Foldable
  90     //////////////////////////////////////////////////////////////////////////
  91     template <>
  92     struct unpack_impl<ext::std::integer_sequence_tag> {
  93         template <typename T, T ...v, typename F>
  94         static constexpr decltype(auto)
  95         apply(std::integer_sequence<T, v...> const&, F&& f) {
  96             return static_cast<F&&>(f)(std::integral_constant<T, v>{}...);
  97         }
  98     };
  99
 100     //////////////////////////////////////////////////////////////////////////
 101     // Iterable
 102     //////////////////////////////////////////////////////////////////////////
 103     template <>
 104     struct at_impl<ext::std::integer_sequence_tag> {
 105         template <typename T, T ...v, typename N>
 106         static constexpr auto apply(std::integer_sequence<T, v...> const&, N const&) {
 107             constexpr std::size_t n = N::value;
 108             constexpr T values[] = {v...};
 109             return std::integral_constant<T, values[n]>{};
 110         }
 111     };
 112
 113     template <>
 114     struct drop_front_impl<ext::std::integer_sequence_tag> {
 115         template <std::size_t n, typename T, T ...t, std::size_t ...i>
 116         static constexpr auto drop_front_helper(std::integer_sequence<T, t...>,
 117                                                 std::index_sequence<i...>)
 118         {
 119             constexpr T ts[sizeof...(t)+1] = {t...}; // avoid 0-sized array
 120             return std::integer_sequence<T, ts[n + i]...>{};
 121         }
 122
 123         template <typename T, T ...t, typename N>
 124         static constexpr auto apply(std::integer_sequence<T, t...> ts, N const&) {
 125             constexpr std::size_t n = N::value;
 126             constexpr std::size_t len = sizeof...(t);
 127             return drop_front_helper<n>(ts,
 128                     std::make_index_sequence<(n < len ? len - n : 0)>{});
 129         }
 130     };
 131
 132     template <>
 133     struct is_empty_impl<ext::std::integer_sequence_tag> {
 134         template <typename T, T ...xs>
 135         static constexpr auto apply(std::integer_sequence<T, xs...> const&)
 136         { return hana::bool_c<sizeof...(xs) == 0>; }
 137     };
 138 BOOST_HANA_NAMESPACE_END
 139
 140 #endif // !BOOST_HANA_EXT_STD_INTEGER_SEQUENCE_HPP