ceph/src/boost/libs/hana/include/boost/hana/tap.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::tap`.
   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_TAP_HPP
  11 #define BOOST_HANA_TAP_HPP
  12
  13 #include <boost/hana/fwd/tap.hpp>
  14
  15 #include <boost/hana/concept/monad.hpp>
  16 #include <boost/hana/config.hpp>
  17 #include <boost/hana/core/dispatch.hpp>
  18 #include <boost/hana/functional/partial.hpp>
  19 #include <boost/hana/lift.hpp>
  20
  21
  22 BOOST_HANA_NAMESPACE_BEGIN
  23     template <typename M>
  24     struct tap_t {
  25     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
  26         static_assert(hana::Monad<M>::value,
  27         "hana::tap<M> requires 'M' to be a Monad");
  28     #endif
  29
  30         template <typename F>
  31         constexpr auto operator()(F&& f) const {
  32             using Tap = BOOST_HANA_DISPATCH_IF(tap_impl<M>,
  33                 hana::Monad<M>::value
  34             );
  35
  36             return Tap::apply(static_cast<F&&>(f));
  37         }
  38     };
  39
  40     namespace detail {
  41         template <typename M>
  42         struct tap_helper {
  43             template <typename F, typename X>
  44             constexpr auto operator()(F&& f, X&& x) const {
  45                 (void)static_cast<F&&>(f)(x);
  46                 return hana::lift<M>(static_cast<X&&>(x));
  47             }
  48         };
  49     }
  50
  51     template <typename M, bool condition>
  52     struct tap_impl<M, when<condition>> : default_ {
  53         template <typename F>
  54         static constexpr auto apply(F&& f)
  55         { return hana::partial(detail::tap_helper<M>{}, static_cast<F&&>(f)); }
  56     };
  57 BOOST_HANA_NAMESPACE_END
  58
  59 #endif // !BOOST_HANA_TAP_HPP