ceph/src/boost/libs/hana/include/boost/hana/duplicate.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::duplicate`.
   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_DUPLICATE_HPP
  11 #define BOOST_HANA_DUPLICATE_HPP
  12
  13 #include <boost/hana/fwd/duplicate.hpp>
  14
  15 #include <boost/hana/concept/comonad.hpp>
  16 #include <boost/hana/config.hpp>
  17 #include <boost/hana/core/dispatch.hpp>
  18 #include <boost/hana/extend.hpp>
  19 #include <boost/hana/functional/id.hpp>
  20
  21
  22 BOOST_HANA_NAMESPACE_BEGIN
  23     //! @cond
  24     template <typename W_>
  25     constexpr decltype(auto) duplicate_t::operator()(W_&& w) const {
  26         using W = typename hana::tag_of<W_>::type;
  27         using Duplicate = BOOST_HANA_DISPATCH_IF(duplicate_impl<W>,
  28             hana::Comonad<W>::value
  29         );
  30
  31     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  32         static_assert(hana::Comonad<W>::value,
  33         "hana::duplicate(w) requires 'w' to be a Comonad");
  34     #endif
  35
  36         return Duplicate::apply(static_cast<W_&&>(w));
  37     }
  38     //! @endcond
  39
  40     template <typename W, bool condition>
  41     struct duplicate_impl<W, when<condition>> : default_ {
  42         template <typename X>
  43         static constexpr decltype(auto) apply(X&& x)
  44         { return hana::extend(static_cast<X&&>(x), hana::id); }
  45     };
  46 BOOST_HANA_NAMESPACE_END
  47
  48 #endif // !BOOST_HANA_DUPLICATE_HPP