ceph/src/boost/libs/hana/include/boost/hana/functional/id.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::id`.
   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_FUNCTIONAL_ID_HPP
  11 #define BOOST_HANA_FUNCTIONAL_ID_HPP
  12
  13 #include <boost/hana/config.hpp>
  14
  15
  16 BOOST_HANA_NAMESPACE_BEGIN
  17     //! @ingroup group-functional
  18     //! The identity function -- returns its argument unchanged.
  19     //!
  20     //! ### Example
  21     //! @include example/functional/id.cpp
  22 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  23     constexpr auto id = [](auto&& x) -> decltype(auto) {
  24         return forwarded(x);
  25     };
  26 #else
  27     struct id_t {
  28         template <typename T>
  29         constexpr T operator()(T&& t) const {
  30             return static_cast<T&&>(t);
  31         }
  32     };
  33
  34     constexpr id_t id{};
  35 #endif
  36 BOOST_HANA_NAMESPACE_END
  37
  38 #endif // !BOOST_HANA_FUNCTIONAL_ID_HPP