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

   1 /*!
   2 @file
   3 Defines `boost::hana::reverse_partial`.
   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_REVERSE_PARTIAL_HPP
  11 #define BOOST_HANA_FUNCTIONAL_REVERSE_PARTIAL_HPP
  12
  13 #include <boost/hana/basic_tuple.hpp>
  14 #include <boost/hana/config.hpp>
  15 #include <boost/hana/detail/decay.hpp>
  16
  17 #include <cstddef>
  18 #include <utility>
  19
  20
  21 BOOST_HANA_NAMESPACE_BEGIN
  22     //! @ingroup group-functional
  23     //! Partially apply a function to some arguments.
  24     //!
  25     //! Given a function `f` and some arguments, `reverse_partial` returns a
  26     //! new function corresponding to `f` whose last arguments are partially
  27     //! applied. Specifically, `reverse_partial(f, x...)` is a function such
  28     //! that
  29     //! @code
  30     //!     reverse_partial(f, x...)(y...) == f(y..., x...)
  31     //! @endcode
  32     //!
  33     //! @note
  34     //! The arity of `f` must match the total number of arguments passed to
  35     //! it, i.e. `sizeof...(x) + sizeof...(y)`.
  36     //!
  37     //!
  38     //! Example
  39     //! -------
  40     //! @include example/functional/reverse_partial.cpp
  41 #ifdef BOOST_HANA_DOXYGEN_INVOKED
  42     constexpr auto reverse_partial = [](auto&& f, auto&& ...x) {
  43         return [perfect-capture](auto&& ...y) -> decltype(auto) {
  44             return forwarded(f)(forwarded(y)..., forwarded(x)...);
  45         };
  46     };
  47 #else
  48     template <typename Indices, typename F, typename ...X>
  49     struct reverse_partial_t;
  50
  51     struct make_reverse_partial_t {
  52         struct secret { };
  53         template <typename F, typename ...X>
  54         constexpr reverse_partial_t<
  55             std::make_index_sequence<sizeof...(X)>,
  56             typename detail::decay<F>::type,
  57             typename detail::decay<X>::type...
  58         > operator()(F&& f, X&& ...x) const {
  59             return {secret{}, static_cast<F&&>(f), static_cast<X&&>(x)...};
  60         }
  61     };
  62
  63     template <std::size_t ...n, typename F, typename ...X>
  64     struct reverse_partial_t<std::index_sequence<n...>, F, X...> {
  65         reverse_partial_t() = default;
  66
  67         template <typename ...T>
  68         constexpr reverse_partial_t(make_reverse_partial_t::secret, T&& ...t)
  69             : storage_{static_cast<T&&>(t)...}
  70         { }
  71
  72         basic_tuple<F, X...> storage_;
  73
  74         template <typename ...Y>
  75         constexpr decltype(auto) operator()(Y&& ...y) const& {
  76             return hana::at_c<0>(storage_)(
  77                 static_cast<Y&&>(y)...,
  78                 hana::at_c<n+1>(storage_)...
  79             );
  80         }
  81
  82         template <typename ...Y>
  83         constexpr decltype(auto) operator()(Y&& ...y) & {
  84             return hana::at_c<0>(storage_)(
  85                 static_cast<Y&&>(y)...,
  86                 hana::at_c<n+1>(storage_)...
  87             );
  88         }
  89
  90         template <typename ...Y>
  91         constexpr decltype(auto) operator()(Y&& ...y) && {
  92             return static_cast<F&&>(hana::at_c<0>(storage_))(
  93                 static_cast<Y&&>(y)...,
  94                 static_cast<X&&>(hana::at_c<n+1>(storage_))...
  95             );
  96         }
  97     };
  98
  99     constexpr make_reverse_partial_t reverse_partial{};
 100 #endif
 101 BOOST_HANA_NAMESPACE_END
 102
 103 #endif // !BOOST_HANA_FUNCTIONAL_REVERSE_PARTIAL_HPP