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

   1 /*!
   2 @file
   3 Forward declares `boost::hana::concat`.
   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_CONCAT_HPP
  11 #define BOOST_HANA_FWD_CONCAT_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/core/when.hpp>
  15
  16
  17 BOOST_HANA_NAMESPACE_BEGIN
  18     //! Combine two monadic structures together.
  19     //! @ingroup group-MonadPlus
  20     //!
  21     //! Given two monadic structures, `concat` combines them together and
  22     //! returns a new monadic structure. The exact definition of `concat`
  23     //! will depend on the exact model of MonadPlus at hand, but for
  24     //! sequences it corresponds intuitively to simple concatenation.
  25     //!
  26     //! Also note that combination is not required to be commutative.
  27     //! In other words, there is no requirement that
  28     //! @code
  29     //!     concat(xs, ys) == concat(ys, xs)
  30     //! @endcode
  31     //! and indeed it does not hold in general.
  32     //!
  33     //!
  34     //! Signature
  35     //! ---------
  36     //! Given a `MonadPlus` `M`, the signature of `concat` is
  37     //! @f$ \mathtt{concat} : M(T) \times M(T) \to M(T) @f$.
  38     //!
  39     //! @param xs, ys
  40     //! Two monadic structures to combine together.
  41     //!
  42     //!
  43     //! Example
  44     //! -------
  45     //! @include example/concat.cpp
  46 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  47     constexpr auto concat = [](auto&& xs, auto&& ys) {
  48         return tag-dispatched;
  49     };
  50 #else
  51     template <typename M, typename = void>
  52     struct concat_impl : concat_impl<M, when<true>> { };
  53
  54     struct concat_t {
  55         template <typename Xs, typename Ys>
  56         constexpr auto operator()(Xs&& xs, Ys&& ys) const;
  57     };
  58
  59     constexpr concat_t concat{};
  60 #endif
  61 BOOST_HANA_NAMESPACE_END
  62
  63 #endif // !BOOST_HANA_FWD_CONCAT_HPP