ceph/src/boost/boost/hana/fwd/none.hpp

   1 /*!
   2 @file
   3 Forward declares `boost::hana::none`.
   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_NONE_HPP
  11 #define BOOST_HANA_FWD_NONE_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/core/when.hpp>
  15
  16
  17 BOOST_HANA_NAMESPACE_BEGIN
  18     //! Returns whether all of the keys of the structure are false-valued.
  19     //! @ingroup group-Searchable
  20     //!
  21     //! The keys of the structure must be `Logical`s. If the structure is not
  22     //! finite, a true-valued key must appear at a finite "index" in order
  23     //! for this method to finish.
  24     //!
  25     //!
  26     //! Example
  27     //! -------
  28     //! @include example/none.cpp
  29 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  30     constexpr auto none = [](auto&& xs) -> decltype(auto) {
  31         return tag-dispatched;
  32     };
  33 #else
  34     template <typename S, typename = void>
  35     struct none_impl : none_impl<S, when<true>> { };
  36
  37     struct none_t {
  38         template <typename Xs>
  39         constexpr auto operator()(Xs&& xs) const;
  40     };
  41
  42     constexpr none_t none{};
  43 #endif
  44 BOOST_HANA_NAMESPACE_END
  45
  46 #endif // !BOOST_HANA_FWD_NONE_HPP