ceph/src/boost/boost/hana/fwd/not.hpp

   1 /*!
   2 @file
   3 Forward declares `boost::hana::not_`.
   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_NOT_HPP
  11 #define BOOST_HANA_FWD_NOT_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/core/when.hpp>
  15
  16
  17 BOOST_HANA_NAMESPACE_BEGIN
  18     //! Negates a `Logical`.
  19     //! @ingroup group-Logical
  20     //!
  21     //! This method returns a `Logical` with the same tag, but whose
  22     //! truth-value is negated. Specifically, `not_(x)` returns a false-valued
  23     //! `Logical` if `x` is a true-valued `Logical`, and a true-valued one
  24     //! otherwise.
  25     //!
  26     //!
  27     //! Example
  28     //! -------
  29     //! @include example/not.cpp
  30 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  31     constexpr auto not_ = [](auto&& x) -> decltype(auto) {
  32         return tag-dispatched;
  33     };
  34 #else
  35     template <typename L, typename = void>
  36     struct not_impl : not_impl<L, when<true>> { };
  37
  38     struct not_t {
  39         template <typename X>
  40         constexpr decltype(auto) operator()(X&& x) const;
  41     };
  42
  43     constexpr not_t not_{};
  44 #endif
  45 BOOST_HANA_NAMESPACE_END
  46
  47 #endif // !BOOST_HANA_FWD_NOT_HPP