ceph/src/boost/boost/hana/fwd/lift.hpp

   1 /*!
   2 @file
   3 Forward declares `boost::hana::lift`.
   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_LIFT_HPP
  11 #define BOOST_HANA_FWD_LIFT_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/core/when.hpp>
  15
  16
  17 namespace boost { namespace hana {
  18     //! Lift a value into an `Applicative` structure.
  19     //! @ingroup group-Applicative
  20     //!
  21     //! `lift<A>` takes a normal value and embeds it into a structure whose
  22     //! shape is represented by the `A` `Applicative`. Note that the value
  23     //! may be a function, in which case the created structure may be
  24     //! `ap`plied to another `Applicative` structure containing values.
  25     //!
  26     //!
  27     //! Signature
  28     //! ---------
  29     //! Given an Applicative `A`, the signature is
  30     //! @f$ \mathtt{lift}_A : T \to A(T) @f$.
  31     //!
  32     //! @tparam A
  33     //! A tag representing the `Applicative` into which the value is lifted.
  34     //!
  35     //! @param x
  36     //! The value to lift into the applicative.
  37     //!
  38     //!
  39     //! Example
  40     //! -------
  41     //! @include example/lift.cpp
  42 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  43     template <typename A>
  44     constexpr auto lift = [](auto&& x) {
  45         return tag-dispatched;
  46     };
  47 #else
  48     template <typename A, typename = void>
  49     struct lift_impl : lift_impl<A, when<true>> { };
  50
  51     template <typename A>
  52     struct lift_t {
  53         template <typename X>
  54         constexpr auto operator()(X&& x) const;
  55     };
  56
  57     template <typename A>
  58     BOOST_HANA_INLINE_VARIABLE constexpr lift_t<A> lift{};
  59 #endif
  60 }} // end namespace boost::hana
  61
  62 #endif // !BOOST_HANA_FWD_LIFT_HPP