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

   1 /*!
   2 @file
   3 Forward declares `boost::hana::is_a` and `boost::hana::is_an`.
   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_IS_A_HPP
  11 #define BOOST_HANA_FWD_CORE_IS_A_HPP
  12
  13 #include <boost/hana/config.hpp>
  14
  15
  16 BOOST_HANA_NAMESPACE_BEGIN
  17     //! @ingroup group-core
  18     //! Returns whether the tag of an object matches a given tag.
  19     //!
  20     //! Given a tag `Tag` and a C++ type `T`, `is_a<Tag, T>` is a compile-time
  21     //! Logical representing whether the tag of `T` is exactly `Tag`. In other
  22     //! words, it is equivalent to
  23     //! @code
  24     //!     std::is_same<Tag, tag_of<T>::type>
  25     //! @endcode
  26     //!
  27     //! For convenience, an alternate syntax is provided for using `is_a`.
  28     //! Specifically, `is_a<Tag>` is a function object returning whether the
  29     //! argument it is passed has the given tag. In other words,
  30     //! @code
  31     //!     is_a<Tag>(x) == is_a<Tag, decltype(x)>
  32     //! @endcode
  33     //!
  34     //!
  35     //! Example
  36     //! -------
  37     //! @include example/core/is_a.cpp
  38 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  39     template <typename Tag, typename optional_T>
  40     constexpr auto is_a = see-documentation;
  41 #else
  42     template <typename Tag, typename ...T>
  43     struct is_a_t;
  44
  45     template <typename Tag, typename ...T>
  46     constexpr is_a_t<Tag, T...> is_a{};
  47 #endif
  48
  49     //! @ingroup group-core
  50     //! Equivalent to `is_a`; provided for consistency with the rules of the
  51     //! English language.
  52 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  53     template <typename Tag, typename ...T>
  54     constexpr auto is_an = is_a<Tag, T...>;
  55 #else
  56     template <typename Tag, typename ...T>
  57     constexpr is_a_t<Tag, T...> is_an{};
  58 #endif
  59 BOOST_HANA_NAMESPACE_END
  60
  61 #endif // !BOOST_HANA_FWD_CORE_IS_A_HPP