ceph/src/boost/boost/hana/drop_front_exactly.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::drop_front_exactly`.
   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_DROP_FRONT_EXACTLY_HPP
  11 #define BOOST_HANA_DROP_FRONT_EXACTLY_HPP
  12
  13 #include <boost/hana/fwd/drop_front_exactly.hpp>
  14
  15 #include <boost/hana/bool.hpp>
  16 #include <boost/hana/concept/integral_constant.hpp>
  17 #include <boost/hana/concept/iterable.hpp>
  18 #include <boost/hana/config.hpp>
  19 #include <boost/hana/core/dispatch.hpp>
  20 #include <boost/hana/drop_front.hpp>
  21 #include <boost/hana/integral_constant.hpp>
  22 #include <boost/hana/is_empty.hpp>
  23
  24
  25 BOOST_HANA_NAMESPACE_BEGIN
  26     //! @cond
  27     template <typename Xs, typename N>
  28     constexpr auto drop_front_exactly_t::operator()(Xs&& xs, N const& n) const {
  29         using It = typename hana::tag_of<Xs>::type;
  30         using DropFrontExactly = BOOST_HANA_DISPATCH_IF(drop_front_exactly_impl<It>,
  31             hana::Iterable<It>::value &&
  32             hana::IntegralConstant<N>::value
  33         );
  34
  35     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  36         static_assert(hana::Iterable<It>::value,
  37         "hana::drop_front_exactly(xs, n) requires 'xs' to be an Iterable");
  38
  39         static_assert(hana::IntegralConstant<N>::value,
  40         "hana::drop_front_exactly(xs, n) requires 'n' to be an IntegralConstant");
  41     #endif
  42
  43         static_assert(N::value >= 0,
  44         "hana::drop_front_exactly(xs, n) requires 'n' to be non-negative");
  45
  46         return DropFrontExactly::apply(static_cast<Xs&&>(xs), n);
  47     }
  48
  49     template <typename Xs>
  50     constexpr auto drop_front_exactly_t::operator()(Xs&& xs) const {
  51         return (*this)(static_cast<Xs&&>(xs), hana::size_c<1>);
  52     }
  53     //! @endcond
  54
  55     namespace detail {
  56         template <typename Xs, typename N>
  57         constexpr void check_dfe_overflow(Xs const& xs, N const&, hana::true_) {
  58             constexpr bool n_overflew_length = decltype(
  59                 hana::is_empty(hana::drop_front(xs, hana::size_c<N::value - 1>))
  60             )::value;
  61             static_assert(!n_overflew_length,
  62             "hana::drop_front_exactly(xs, n) requires 'n' to be less than or "
  63             "equal to the number of elements in 'xs'");
  64         }
  65
  66         template <typename Xs, typename N>
  67         constexpr void check_dfe_overflow(Xs const&, N const&, hana::false_) { }
  68     }
  69
  70     template <typename It, bool condition>
  71     struct drop_front_exactly_impl<It, when<condition>> : default_ {
  72         template <typename Xs, typename N>
  73         static constexpr auto apply(Xs&& xs, N const& n) {
  74             auto result = hana::drop_front(static_cast<Xs&&>(xs), n);
  75             constexpr bool check_for_overflow =
  76                 decltype(hana::is_empty(result))::value && N::value != 0;
  77
  78             detail::check_dfe_overflow(xs, n, hana::bool_c<check_for_overflow>);
  79
  80             return result; // NRVO applied
  81         }
  82     };
  83 BOOST_HANA_NAMESPACE_END
  84
  85 #endif // !BOOST_HANA_DROP_FRONT_EXACTLY_HPP