ceph/src/boost/boost/hana/fwd/core/default.hpp

   1 /*!
   2 @file
   3 Forward declares `boost::hana::default_` and `boost::hana::is_default`.
   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_CORE_DEFAULT_HPP
  11 #define BOOST_HANA_FWD_CORE_DEFAULT_HPP
  12
  13 #include <boost/hana/config.hpp>
  14
  15
  16 BOOST_HANA_NAMESPACE_BEGIN
  17     //! @ingroup group-core
  18     //! Mark a tag-dispatched method implementation as a default implementation.
  19     //!
  20     //! When defining a new concept with tag-dispatched methods, it is
  21     //! sometimes possible to provide a default implementation for some
  22     //! method(s). Making `default_` a base class of such a default
  23     //! implementation makes it possible to detect whether the method
  24     //! was dispatched to the default implementation afterwards.
  25     //!
  26     //!
  27     //! Example
  28     //! -------
  29     //! @include example/core/default.cpp
  30     struct default_ { };
  31
  32     //! @ingroup group-core
  33     //! Returns whether a tag-dispatched method implementation is a default
  34     //! implementation.
  35     //!
  36     //! Given a tag-dispatched method implementation `method_impl<T...>`,
  37     //! `is_default<method_impl<T...>>` returns whether `method_impl<T...>`
  38     //! is a default implementation. Note that if there is no default
  39     //! implementation for the method, then `is_default` should not be
  40     //! used unless a static assertion saying that "the method is not
  41     //! implemented" is acceptable.
  42     //!
  43     //!
  44     //! Example
  45     //! -------
  46     //! @include example/core/default.cpp
  47 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  48     template <typename Method>
  49     struct is_default { see documentation };
  50 #else
  51     template <typename T, typename = void>
  52     struct is_default;
  53 #endif
  54 BOOST_HANA_NAMESPACE_END
  55
  56 #endif // !BOOST_HANA_FWD_CORE_DEFAULT_HPP