ceph/src/boost/boost/hana/functional/overload_linearly.hpp

   1 /*!
   2 @file
   3 Defines `boost::hana::overload_linearly`.
   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_FUNCTIONAL_OVERLOAD_LINEARLY_HPP
  11 #define BOOST_HANA_FUNCTIONAL_OVERLOAD_LINEARLY_HPP
  12
  13 #include <boost/hana/config.hpp>
  14 #include <boost/hana/detail/decay.hpp>
  15
  16 #include <utility>
  17
  18
  19 BOOST_HANA_NAMESPACE_BEGIN
  20     //! @ingroup group-functional
  21     //! Call the first function that produces a valid call expression.
  22     //!
  23     //! Given functions `f1, ..., fn`, `overload_linearly(f1, ..., fn)` is
  24     //! a new function that calls the first `fk` producing a valid call
  25     //! expression with the given arguments. Specifically,
  26     //! @code
  27     //!     overload_linearly(f1, ..., fn)(args...) == fk(args...)
  28     //! @endcode
  29     //!
  30     //! where `fk` is the _first_ function such that `fk(args...)` is a valid
  31     //! expression.
  32     //!
  33     //!
  34     //! Example
  35     //! -------
  36     //! @include example/functional/overload_linearly.cpp
  37 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  38     constexpr auto overload_linearly = [](auto&& f1, auto&& f2, ..., auto&& fn) {
  39         return [perfect-capture](auto&& ...x) -> decltype(auto) {
  40             return forwarded(fk)(forwarded(x)...);
  41         };
  42     };
  43 #else
  44     template <typename F, typename G>
  45     struct overload_linearly_t {
  46         F f;
  47         G g;
  48
  49     private:
  50         template <typename ...Args, typename =
  51             decltype(std::declval<F const&>()(std::declval<Args>()...))>
  52         constexpr F const& which(int) const& { return f; }
  53
  54         template <typename ...Args, typename =
  55             decltype(std::declval<F&>()(std::declval<Args>()...))>
  56         constexpr F& which(int) & { return f; }
  57
  58         template <typename ...Args, typename =
  59             decltype(std::declval<F&&>()(std::declval<Args>()...))>
  60         constexpr F which(int) && { return static_cast<F&&>(f); }
  61
  62         template <typename ...Args>
  63         constexpr G const& which(long) const& { return g; }
  64
  65         template <typename ...Args>
  66         constexpr G& which(long) & { return g; }
  67
  68         template <typename ...Args>
  69         constexpr G which(long) && { return static_cast<G&&>(g); }
  70
  71     public:
  72         template <typename ...Args>
  73         constexpr decltype(auto) operator()(Args&& ...args) const&
  74         { return which<Args...>(int{})(static_cast<Args&&>(args)...); }
  75
  76         template <typename ...Args>
  77         constexpr decltype(auto) operator()(Args&& ...args) &
  78         { return which<Args...>(int{})(static_cast<Args&&>(args)...); }
  79
  80         template <typename ...Args>
  81         constexpr decltype(auto) operator()(Args&& ...args) &&
  82         { return which<Args...>(int{})(static_cast<Args&&>(args)...); }
  83     };
  84
  85     struct make_overload_linearly_t {
  86         template <typename F, typename G>
  87         constexpr overload_linearly_t<
  88             typename detail::decay<F>::type,
  89             typename detail::decay<G>::type
  90         > operator()(F&& f, G&& g) const {
  91             return {static_cast<F&&>(f), static_cast<G&&>(g)};
  92         }
  93
  94         template <typename F, typename G, typename ...H>
  95         constexpr decltype(auto) operator()(F&& f, G&& g, H&& ...h) const {
  96             return (*this)(static_cast<F&&>(f),
  97                     (*this)(static_cast<G&&>(g), static_cast<H&&>(h)...));
  98         }
  99
 100         template <typename F>
 101         constexpr typename detail::decay<F>::type operator()(F&& f) const {
 102             return static_cast<F&&>(f);
 103         }
 104     };
 105
 106     constexpr make_overload_linearly_t overload_linearly{};
 107 #endif
 108 BOOST_HANA_NAMESPACE_END
 109
 110 #endif // !BOOST_HANA_FUNCTIONAL_OVERLOAD_LINEARLY_HPP