ceph/src/boost/libs/hana/include/boost/hana/length.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::length`.
   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_LENGTH_HPP
  11 #define BOOST_HANA_LENGTH_HPP
  12
  13 #include <boost/hana/fwd/length.hpp>
  14
  15 #include <boost/hana/concept/foldable.hpp>
  16 #include <boost/hana/config.hpp>
  17 #include <boost/hana/core/dispatch.hpp>
  18 #include <boost/hana/integral_constant.hpp>
  19 #include <boost/hana/unpack.hpp>
  20
  21
  22 BOOST_HANA_NAMESPACE_BEGIN
  23     //! @cond
  24     template <typename Xs>
  25     constexpr auto length_t::operator()(Xs const& xs) const {
  26         using S = typename hana::tag_of<Xs>::type;
  27         using Length = BOOST_HANA_DISPATCH_IF(length_impl<S>,
  28             hana::Foldable<S>::value
  29         );
  30
  31     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  32         static_assert(hana::Foldable<S>::value,
  33         "hana::length(xs) requires 'xs' to be Foldable");
  34     #endif
  35
  36         return Length::apply(xs);
  37     }
  38     //! @endcond
  39
  40     namespace detail {
  41         struct argn {
  42             template <typename ...Xs>
  43             constexpr hana::size_t<sizeof...(Xs)> operator()(Xs const& ...) const
  44             { return {}; }
  45         };
  46     }
  47
  48     template <typename T, bool condition>
  49     struct length_impl<T, when<condition>> : default_ {
  50         template <typename Xs>
  51         static constexpr auto apply(Xs const& xs) {
  52             return hana::unpack(xs, detail::argn{});
  53         }
  54     };
  55 BOOST_HANA_NAMESPACE_END
  56
  57 #endif // !BOOST_HANA_LENGTH_HPP