ceph/src/boost/boost/hana/fwd/one.hpp

   1 /*!
   2 @file
   3 Forward declares `boost::hana::one`.
   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_ONE_HPP
  11 #define BOOST_HANA_FWD_ONE_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/core/when.hpp>
  15
  16
  17 BOOST_HANA_NAMESPACE_BEGIN
  18     //! Identity of the `Ring` multiplication.
  19     //! @ingroup group-Ring
  20     //!
  21     //! @tparam R
  22     //! The tag (must be a model of `Ring`) of the returned identity.
  23     //!
  24     //!
  25     //! Example
  26     //! -------
  27     //! @include example/one.cpp
  28 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  29     template <typename R>
  30     constexpr auto one = []() -> decltype(auto) {
  31         return tag-dispatched;
  32     };
  33 #else
  34     template <typename R, typename = void>
  35     struct one_impl : one_impl<R, when<true>> { };
  36
  37     template <typename R>
  38     struct one_t;
  39
  40     template <typename R>
  41     constexpr one_t<R> one{};
  42 #endif
  43 BOOST_HANA_NAMESPACE_END
  44
  45 #endif // !BOOST_HANA_FWD_ONE_HPP