ceph/src/boost/libs/hana/include/boost/hana/fwd/union.hpp

   1 /*!
   2 @file
   3 Forward declares `boost::hana::union_`.
   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_FWD_UNION_HPP
  11 #define BOOST_HANA_FWD_UNION_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/core/when.hpp>
  15
  16
  17 BOOST_HANA_NAMESPACE_BEGIN
  18     //! Returns the union of two sets.
  19     //! @relates hana::set
  20     //!
  21     //! Given two sets `xs` and `ys`, `union_(xs, ys)` is a new set containing
  22     //! all the elements of `xs` and all the elements of `ys`, without
  23     //! duplicates. For any object `x`, the following holds:
  24     //! @code
  25     //!     x ^in^ union_(xs, ys) if and only if x ^in^ xs || x ^in^ ys
  26     //! @endcode
  27     //!
  28     //!
  29     //! @param xs, ys
  30     //! Two sets to compute the union of.
  31     //!
  32     //!
  33     //! Example
  34     //! -------
  35     //! @include example/union.cpp
  36 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  37     constexpr auto union_ = [](auto&& xs, auto&& ys) {
  38         return tag-dispatched;
  39     };
  40 #else
  41     template <typename S, typename = void>
  42     struct union_impl : union_impl<S, when<true>> { };
  43
  44     struct union_t {
  45         template <typename Xs, typename Ys>
  46         constexpr auto operator()(Xs&& xs, Ys&& ys) const;
  47     };
  48
  49     constexpr union_t union_{};
  50 #endif
  51 BOOST_HANA_NAMESPACE_END
  52
  53 #endif // !BOOST_HANA_FWD_UNION_HPP