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

   1 /*!
   2 @file
   3 Defines `boost::hana::lazy`.
   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_LAZY_HPP
  11 #define BOOST_HANA_LAZY_HPP
  12
  13 #include <boost/hana/fwd/lazy.hpp>
  14
  15 #include <boost/hana/basic_tuple.hpp>
  16 #include <boost/hana/config.hpp>
  17 #include <boost/hana/core/make.hpp>
  18 #include <boost/hana/detail/decay.hpp>
  19 #include <boost/hana/detail/operators/adl.hpp>
  20 #include <boost/hana/detail/operators/monad.hpp>
  21 #include <boost/hana/functional/apply.hpp>
  22 #include <boost/hana/functional/compose.hpp>
  23 #include <boost/hana/functional/on.hpp>
  24 #include <boost/hana/fwd/ap.hpp>
  25 #include <boost/hana/fwd/duplicate.hpp>
  26 #include <boost/hana/fwd/eval.hpp>
  27 #include <boost/hana/fwd/extend.hpp>
  28 #include <boost/hana/fwd/extract.hpp>
  29 #include <boost/hana/fwd/flatten.hpp>
  30 #include <boost/hana/fwd/lift.hpp>
  31 #include <boost/hana/fwd/transform.hpp>
  32
  33 #include <cstddef>
  34 #include <type_traits>
  35 #include <utility>
  36
  37
  38 BOOST_HANA_NAMESPACE_BEGIN
  39     //////////////////////////////////////////////////////////////////////////
  40     // lazy
  41     //////////////////////////////////////////////////////////////////////////
  42     template <typename Indices, typename F, typename ...Args>
  43     struct lazy_apply_t;
  44
  45     namespace detail { struct lazy_secret { }; }
  46
  47     template <std::size_t ...n, typename F, typename ...Args>
  48     struct lazy_apply_t<std::index_sequence<n...>, F, Args...>
  49         : detail::operators::adl<>
  50     {
  51         template <typename ...T>
  52         constexpr lazy_apply_t(detail::lazy_secret, T&& ...t)
  53             : storage_{static_cast<T&&>(t)...}
  54         { }
  55
  56         basic_tuple<F, Args...> storage_;
  57         using hana_tag = lazy_tag;
  58     };
  59
  60     template <typename X>
  61     struct lazy_value_t : detail::operators::adl<> {
  62         template <typename Y>
  63         constexpr lazy_value_t(detail::lazy_secret, Y&& y)
  64             : storage_{static_cast<Y&&>(y)}
  65         { }
  66
  67         basic_tuple<X> storage_;
  68         using hana_tag = lazy_tag;
  69
  70         // If this is called, we assume that `X` is in fact a function.
  71         template <typename ...Args>
  72         constexpr lazy_apply_t<
  73             std::make_index_sequence<sizeof...(Args)>,
  74             X, typename detail::decay<Args>::type...
  75         > operator()(Args&& ...args) const& {
  76             return {detail::lazy_secret{},
  77                     hana::get_impl<0>(storage_), static_cast<Args&&>(args)...};
  78         }
  79
  80         template <typename ...Args>
  81         constexpr lazy_apply_t<
  82             std::make_index_sequence<sizeof...(Args)>,
  83             X, typename detail::decay<Args>::type...
  84         > operator()(Args&& ...args) && {
  85             return {detail::lazy_secret{},
  86                 static_cast<X&&>(hana::get_impl<0>(storage_)),
  87                 static_cast<Args&&>(args)...
  88             };
  89         }
  90     };
  91
  92     //////////////////////////////////////////////////////////////////////////
  93     // make<lazy_tag>
  94     //////////////////////////////////////////////////////////////////////////
  95     template <>
  96     struct make_impl<lazy_tag> {
  97         template <typename X>
  98         static constexpr lazy_value_t<typename detail::decay<X>::type> apply(X&& x) {
  99             return {detail::lazy_secret{}, static_cast<X&&>(x)};
 100         }
 101     };
 102
 103     //////////////////////////////////////////////////////////////////////////
 104     // Operators
 105     //////////////////////////////////////////////////////////////////////////
 106     namespace detail {
 107         template <>
 108         struct monad_operators<lazy_tag> { static constexpr bool value = true; };
 109     }
 110
 111     //////////////////////////////////////////////////////////////////////////
 112     // eval for lazy_tag
 113     //////////////////////////////////////////////////////////////////////////
 114     template <>
 115     struct eval_impl<lazy_tag> {
 116         // lazy_apply_t
 117         template <std::size_t ...n, typename F, typename ...Args>
 118         static constexpr decltype(auto)
 119         apply(lazy_apply_t<std::index_sequence<n...>, F, Args...> const& expr) {
 120             return hana::get_impl<0>(expr.storage_)(
 121                 hana::get_impl<n+1>(expr.storage_)...
 122             );
 123         }
 124
 125         template <std::size_t ...n, typename F, typename ...Args>
 126         static constexpr decltype(auto)
 127         apply(lazy_apply_t<std::index_sequence<n...>, F, Args...>& expr) {
 128             return hana::get_impl<0>(expr.storage_)(
 129                 hana::get_impl<n+1>(expr.storage_)...
 130             );
 131         }
 132
 133         template <std::size_t ...n, typename F, typename ...Args>
 134         static constexpr decltype(auto)
 135         apply(lazy_apply_t<std::index_sequence<n...>, F, Args...>&& expr) {
 136             return static_cast<F&&>(hana::get_impl<0>(expr.storage_))(
 137                 static_cast<Args&&>(hana::get_impl<n+1>(expr.storage_))...
 138             );
 139         }
 140
 141         // lazy_value_t
 142         template <typename X>
 143         static constexpr X const& apply(lazy_value_t<X> const& expr)
 144         { return hana::get_impl<0>(expr.storage_); }
 145
 146         template <typename X>
 147         static constexpr X& apply(lazy_value_t<X>& expr)
 148         { return hana::get_impl<0>(expr.storage_); }
 149
 150         template <typename X>
 151         static constexpr X apply(lazy_value_t<X>&& expr)
 152         { return static_cast<X&&>(hana::get_impl<0>(expr.storage_)); }
 153     };
 154
 155     //////////////////////////////////////////////////////////////////////////
 156     // Functor
 157     //////////////////////////////////////////////////////////////////////////
 158     template <>
 159     struct transform_impl<lazy_tag> {
 160         template <typename Expr, typename F>
 161         static constexpr auto apply(Expr&& expr, F&& f) {
 162             return hana::make_lazy(hana::compose(static_cast<F&&>(f), hana::eval))(
 163                 static_cast<Expr&&>(expr)
 164             );
 165         }
 166     };
 167
 168     //////////////////////////////////////////////////////////////////////////
 169     // Applicative
 170     //////////////////////////////////////////////////////////////////////////
 171     template <>
 172     struct lift_impl<lazy_tag> {
 173         template <typename X>
 174         static constexpr lazy_value_t<typename detail::decay<X>::type>
 175         apply(X&& x) {
 176             return {detail::lazy_secret{}, static_cast<X&&>(x)};
 177         }
 178     };
 179
 180     template <>
 181     struct ap_impl<lazy_tag> {
 182         template <typename F, typename X>
 183         static constexpr decltype(auto) apply(F&& f, X&& x) {
 184             return hana::make_lazy(hana::on(hana::apply, hana::eval))(
 185                 static_cast<F&&>(f), static_cast<X&&>(x)
 186             );
 187         }
 188     };
 189
 190     //////////////////////////////////////////////////////////////////////////
 191     // Monad
 192     //////////////////////////////////////////////////////////////////////////
 193     template <>
 194     struct flatten_impl<lazy_tag> {
 195         template <typename Expr>
 196         static constexpr decltype(auto) apply(Expr&& expr) {
 197             return hana::make_lazy(hana::compose(hana::eval, hana::eval))(
 198                 static_cast<Expr&&>(expr)
 199             );
 200         }
 201     };
 202
 203     //////////////////////////////////////////////////////////////////////////
 204     // Comonad
 205     //////////////////////////////////////////////////////////////////////////
 206     template <>
 207     struct extract_impl<lazy_tag> {
 208         template <typename Expr>
 209         static constexpr decltype(auto) apply(Expr&& expr)
 210         { return hana::eval(static_cast<Expr&&>(expr)); }
 211     };
 212
 213     template <>
 214     struct duplicate_impl<lazy_tag> {
 215         template <typename Expr>
 216         static constexpr decltype(auto) apply(Expr&& expr)
 217         { return hana::make_lazy(static_cast<Expr&&>(expr)); }
 218     };
 219
 220     template <>
 221     struct extend_impl<lazy_tag> {
 222         template <typename Expr, typename F>
 223         static constexpr decltype(auto) apply(Expr&& expr, F&& f) {
 224             return hana::make_lazy(static_cast<F&&>(f))(static_cast<Expr&&>(expr));
 225         }
 226     };
 227 BOOST_HANA_NAMESPACE_END
 228
 229 #endif // !BOOST_HANA_LAZY_HPP