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

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