ceph/src/boost/boost/hana/core/make.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::make`.
   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_CORE_MAKE_HPP
  11 #define BOOST_HANA_CORE_MAKE_HPP
  12
  13 #include <boost/hana/fwd/core/make.hpp>
  14
  15 #include <boost/hana/config.hpp>
  16 #include <boost/hana/core/default.hpp>
  17 #include <boost/hana/core/when.hpp>
  18
  19
  20 BOOST_HANA_NAMESPACE_BEGIN
  21     //! @cond
  22     template <typename Datatype, typename>
  23     struct make_impl : make_impl<Datatype, when<true>> { };
  24     //! @endcond
  25
  26     template <typename Datatype, bool condition>
  27     struct make_impl<Datatype, when<condition>> : default_ {
  28         template <typename ...X>
  29         static constexpr auto make_helper(int, X&& ...x)
  30             -> decltype(Datatype(static_cast<X&&>(x)...))
  31         { return Datatype(static_cast<X&&>(x)...); }
  32
  33         template <typename ...X>
  34         static constexpr auto make_helper(long, X&& ...) {
  35             static_assert((sizeof...(X), false),
  36             "there exists no constructor for the given data type");
  37         }
  38
  39         template <typename ...X>
  40         static constexpr decltype(auto) apply(X&& ...x)
  41         { return make_helper(int{}, static_cast<X&&>(x)...); }
  42     };
  43 BOOST_HANA_NAMESPACE_END
  44
  45 #endif // !BOOST_HANA_CORE_MAKE_HPP