ceph/src/boost/boost/outcome/detail/basic_result_storage.hpp

   1 /* Storage for a very simple basic_result type
   2 (C) 2017-2020 Niall Douglas <http://www.nedproductions.biz/> (6 commits)
   3 File Created: Oct 2017
   4
   5
   6 Boost Software License - Version 1.0 - August 17th, 2003
   7
   8 Permission is hereby granted, free of charge, to any person or organization
   9 obtaining a copy of the software and accompanying documentation covered by
  10 this license (the "Software") to use, reproduce, display, distribute,
  11 execute, and transmit the Software, and to prepare derivative works of the
  12 Software, and to permit third-parties to whom the Software is furnished to
  13 do so, all subject to the following:
  14
  15 The copyright notices in the Software and this entire statement, including
  16 the above license grant, this restriction and the following disclaimer,
  17 must be included in all copies of the Software, in whole or in part, and
  18 all derivative works of the Software, unless such copies or derivative
  19 works are solely in the form of machine-executable object code generated by
  20 a source language processor.
  21
  22 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  23 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  24 FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
  25 SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
  26 FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
  27 ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  28 DEALINGS IN THE SOFTWARE.
  29 */
  30
  31 #ifndef BOOST_OUTCOME_BASIC_RESULT_STORAGE_HPP
  32 #define BOOST_OUTCOME_BASIC_RESULT_STORAGE_HPP
  33
  34 #include "../success_failure.hpp"
  35 #include "../trait.hpp"
  36 #include "value_storage.hpp"
  37
  38 BOOST_OUTCOME_V2_NAMESPACE_EXPORT_BEGIN
  39
  40 namespace detail
  41 {
  42   template <class State, class E> constexpr inline void _set_error_is_errno(State & /*unused*/, const E & /*unused*/) {}
  43   template <class R, class EC, class NoValuePolicy> class basic_result_storage;
  44 }  // namespace detail
  45
  46 namespace hooks
  47 {
  48   template <class R, class S, class NoValuePolicy> constexpr inline uint16_t spare_storage(const detail::basic_result_storage<R, S, NoValuePolicy> *r) noexcept;
  49   template <class R, class S, class NoValuePolicy>
  50   constexpr inline void set_spare_storage(detail::basic_result_storage<R, S, NoValuePolicy> *r, uint16_t v) noexcept;
  51 }  // namespace hooks
  52
  53 namespace policy
  54 {
  55   struct base;
  56 }  // namespace policy
  57
  58 namespace detail
  59 {
  60   template <bool value_throws, bool error_throws> struct basic_result_storage_swap;
  61   template <class R, class EC, class NoValuePolicy>  //
  62   class basic_result_storage
  63   {
  64     static_assert(trait::type_can_be_used_in_basic_result<R>, "The type R cannot be used in a basic_result");
  65     static_assert(trait::type_can_be_used_in_basic_result<EC>, "The type S cannot be used in a basic_result");
  66     static_assert(std::is_void<EC>::value || std::is_default_constructible<EC>::value, "The type S must be void or default constructible");
  67
  68     friend struct policy::base;
  69     template <class T, class U, class V>  //
  70     friend class basic_result_storage;
  71     template <class T, class U, class V> friend class basic_result_final;
  72     template <class T, class U, class V>
  73     friend constexpr inline uint16_t hooks::spare_storage(const detail::basic_result_storage<T, U, V> *r) noexcept;  // NOLINT
  74     template <class T, class U, class V>
  75     friend constexpr inline void hooks::set_spare_storage(detail::basic_result_storage<T, U, V> *r, uint16_t v) noexcept;  // NOLINT
  76     template <bool value_throws, bool error_throws> struct basic_result_storage_swap;
  77
  78     struct disable_in_place_value_type
  79     {
  80     };
  81     struct disable_in_place_error_type
  82     {
  83     };
  84
  85   protected:
  86     using _value_type = std::conditional_t<std::is_same<R, EC>::value, disable_in_place_value_type, R>;
  87     using _error_type = std::conditional_t<std::is_same<R, EC>::value, disable_in_place_error_type, EC>;
  88
  89     using _state_type = value_storage_select_impl<_value_type>;
  90
  91 #ifdef BOOST_OUTCOME_STANDARDESE_IS_IN_THE_HOUSE
  92     detail::value_storage_trivial<_value_type> _state;
  93 #else
  94     _state_type _state;
  95 #endif
  96     devoid<_error_type> _error;
  97
  98   public:
  99     // Used by iostream support to access state
 100     _state_type &_iostreams_state() { return _state; }
 101     const _state_type &_iostreams_state() const { return _state; }
 102
 103     // Hack to work around MSVC bug in /permissive-
 104     _state_type &_msvc_nonpermissive_state() { return _state; }
 105     devoid<_error_type> &_msvc_nonpermissive_error() { return _error; }
 106
 107   protected:
 108     basic_result_storage() = default;
 109     basic_result_storage(const basic_result_storage &) = default;             // NOLINT
 110     basic_result_storage(basic_result_storage &&) = default;                  // NOLINT
 111     basic_result_storage &operator=(const basic_result_storage &) = default;  // NOLINT
 112     basic_result_storage &operator=(basic_result_storage &&) = default;       // NOLINT
 113     ~basic_result_storage() = default;
 114
 115     template <class... Args>
 116     constexpr explicit basic_result_storage(in_place_type_t<_value_type> _,
 117                                             Args &&... args) noexcept(detail::is_nothrow_constructible<_value_type, Args...>)
 118         : _state{_, static_cast<Args &&>(args)...}
 119         , _error()
 120     {
 121     }
 122     template <class U, class... Args>
 123     constexpr basic_result_storage(in_place_type_t<_value_type> _, std::initializer_list<U> il,
 124                                    Args &&... args) noexcept(detail::is_nothrow_constructible<_value_type, std::initializer_list<U>, Args...>)
 125         : _state{_, il, static_cast<Args &&>(args)...}
 126         , _error()
 127     {
 128     }
 129     template <class... Args>
 130     constexpr explicit basic_result_storage(in_place_type_t<_error_type> /*unused*/, Args &&... args) noexcept(detail::is_nothrow_constructible<_error_type, Args...>)
 131         : _state{detail::status::have_error}
 132         , _error(static_cast<Args &&>(args)...)
 133     {
 134       _set_error_is_errno(_state, _error);
 135     }
 136     template <class U, class... Args>
 137     constexpr basic_result_storage(in_place_type_t<_error_type> /*unused*/, std::initializer_list<U> il, Args &&... args) noexcept(detail::is_nothrow_constructible<_error_type, std::initializer_list<U>, Args...>)
 138         : _state{detail::status::have_error}
 139         , _error{il, static_cast<Args &&>(args)...}
 140     {
 141       _set_error_is_errno(_state, _error);
 142     }
 143     struct compatible_conversion_tag
 144     {
 145     };
 146     template <class T, class U, class V>
 147     constexpr basic_result_storage(compatible_conversion_tag /*unused*/, const basic_result_storage<T, U, V> &o) noexcept(detail::is_nothrow_constructible<_value_type, T> &&detail::is_nothrow_constructible<_error_type, U>)
 148         : _state(o._state)
 149         , _error(o._error)
 150     {
 151     }
 152     template <class T, class V>
 153     constexpr basic_result_storage(compatible_conversion_tag /*unused*/, const basic_result_storage<T, void, V> &o) noexcept(detail::is_nothrow_constructible<_value_type, T>)
 154         : _state(o._state)
 155         , _error(_error_type{})
 156     {
 157     }
 158     template <class T, class U, class V>
 159     constexpr basic_result_storage(compatible_conversion_tag /*unused*/, basic_result_storage<T, U, V> &&o) noexcept(detail::is_nothrow_constructible<_value_type, T> &&detail::is_nothrow_constructible<_error_type, U>)
 160         : _state(static_cast<decltype(o._state) &&>(o._state))
 161         , _error(static_cast<U &&>(o._error))
 162     {
 163     }
 164     template <class T, class V>
 165     constexpr basic_result_storage(compatible_conversion_tag /*unused*/, basic_result_storage<T, void, V> &&o) noexcept(detail::is_nothrow_constructible<_value_type, T>)
 166         : _state(static_cast<decltype(o._state) &&>(o._state))
 167         , _error(_error_type{})
 168     {
 169     }
 170
 171     struct make_error_code_compatible_conversion_tag
 172     {
 173     };
 174     template <class T, class U, class V>
 175     constexpr basic_result_storage(make_error_code_compatible_conversion_tag /*unused*/, const basic_result_storage<T, U, V> &o) noexcept(detail::is_nothrow_constructible<_value_type, T> &&noexcept(make_error_code(std::declval<U>())))
 176         : _state(o._state)
 177         , _error(make_error_code(o._error))
 178     {
 179     }
 180     template <class T, class U, class V>
 181     constexpr basic_result_storage(make_error_code_compatible_conversion_tag /*unused*/, basic_result_storage<T, U, V> &&o) noexcept(detail::is_nothrow_constructible<_value_type, T> &&noexcept(make_error_code(std::declval<U>())))
 182         : _state(static_cast<decltype(o._state) &&>(o._state))
 183         , _error(make_error_code(static_cast<U &&>(o._error)))
 184     {
 185     }
 186
 187     struct make_exception_ptr_compatible_conversion_tag
 188     {
 189     };
 190     template <class T, class U, class V>
 191     constexpr basic_result_storage(make_exception_ptr_compatible_conversion_tag /*unused*/, const basic_result_storage<T, U, V> &o) noexcept(detail::is_nothrow_constructible<_value_type, T> &&noexcept(make_exception_ptr(std::declval<U>())))
 192         : _state(o._state)
 193         , _error(make_exception_ptr(o._error))
 194     {
 195     }
 196     template <class T, class U, class V>
 197     constexpr basic_result_storage(make_exception_ptr_compatible_conversion_tag /*unused*/, basic_result_storage<T, U, V> &&o) noexcept(detail::is_nothrow_constructible<_value_type, T> &&noexcept(make_exception_ptr(std::declval<U>())))
 198         : _state(static_cast<decltype(o._state) &&>(o._state))
 199         , _error(make_exception_ptr(static_cast<U &&>(o._error)))
 200     {
 201     }
 202   };
 203
 204 // Neither value nor error type can throw during swap
 205 #ifndef BOOST_NO_EXCEPTIONS
 206   template <> struct basic_result_storage_swap<false, false>
 207 #else
 208   template <bool value_throws, bool error_throws> struct basic_result_storage_swap
 209 #endif
 210   {
 211     template <class R, class EC, class NoValuePolicy> constexpr basic_result_storage_swap(basic_result_storage<R, EC, NoValuePolicy> &a, basic_result_storage<R, EC, NoValuePolicy> &b)
 212     {
 213       using std::swap;
 214       a._msvc_nonpermissive_state().swap(b._msvc_nonpermissive_state());
 215       swap(a._msvc_nonpermissive_error(), b._msvc_nonpermissive_error());
 216     }
 217   };
 218 #ifndef BOOST_NO_EXCEPTIONS
 219   // Swap potentially throwing value first
 220   template <> struct basic_result_storage_swap<true, false>
 221   {
 222     template <class R, class EC, class NoValuePolicy> constexpr basic_result_storage_swap(basic_result_storage<R, EC, NoValuePolicy> &a, basic_result_storage<R, EC, NoValuePolicy> &b)
 223     {
 224       using std::swap;
 225       a._msvc_nonpermissive_state().swap(b._msvc_nonpermissive_state());
 226       swap(a._msvc_nonpermissive_error(), b._msvc_nonpermissive_error());
 227     }
 228   };
 229   // Swap potentially throwing error first
 230   template <> struct basic_result_storage_swap<false, true>
 231   {
 232     template <class R, class EC, class NoValuePolicy> constexpr basic_result_storage_swap(basic_result_storage<R, EC, NoValuePolicy> &a, basic_result_storage<R, EC, NoValuePolicy> &b)
 233     {
 234       struct _
 235       {
 236         status_bitfield_type &a, &b;
 237         bool all_good{false};
 238         ~_()
 239         {
 240           if(!all_good)
 241           {
 242             // We lost one of the values
 243             a.set_have_lost_consistency(true);
 244             b.set_have_lost_consistency(true);
 245           }
 246         }
 247       } _{a._msvc_nonpermissive_state()._status, b._msvc_nonpermissive_state()._status};
 248       strong_swap(_.all_good, a._msvc_nonpermissive_error(), b._msvc_nonpermissive_error());
 249       a._msvc_nonpermissive_state().swap(b._msvc_nonpermissive_state());
 250     }
 251   };
 252   // Both could throw
 253   template <> struct basic_result_storage_swap<true, true>
 254   {
 255     template <class R, class EC, class NoValuePolicy> basic_result_storage_swap(basic_result_storage<R, EC, NoValuePolicy> &a, basic_result_storage<R, EC, NoValuePolicy> &b)
 256     {
 257       using std::swap;
 258       // Swap value and status first, if it throws, status will remain unchanged
 259       a._msvc_nonpermissive_state().swap(b._msvc_nonpermissive_state());
 260       bool all_good = false;
 261       try
 262       {
 263         strong_swap(all_good, a._msvc_nonpermissive_error(), b._msvc_nonpermissive_error());
 264       }
 265       catch(...)
 266       {
 267         if(!all_good)
 268         {
 269           a._msvc_nonpermissive_state()._status.set_have_lost_consistency(true);
 270           b._msvc_nonpermissive_state()._status.set_have_lost_consistency(true);
 271         }
 272         else
 273         {
 274           // We may still be able to rescue tis
 275           // First try to put the value and status back
 276           try
 277           {
 278             a._msvc_nonpermissive_state().swap(b._msvc_nonpermissive_state());
 279             // If that succeeded, continue by rethrowing the exception
 280           }
 281           catch(...)
 282           {
 283             all_good = false;
 284           }
 285         }
 286         if(!all_good)
 287         {
 288           // We are now trapped. The value swapped, the error did not,
 289           // trying to restore the value failed. We now have
 290           // inconsistent result objects. Best we can do is fix up the
 291           // status bits to prevent has_value() == has_error().
 292           auto check = [](basic_result_storage<R, EC, NoValuePolicy> &x) {
 293             bool has_value = x._state._status.have_value();
 294             bool has_error = x._state._status.have_error();
 295             bool has_exception = x._state._status.have_exception();
 296             x._state._status.set_have_lost_consistency(true);
 297             if(has_value == (has_error || has_exception))
 298             {
 299               if(has_value)
 300               {
 301                 // We know the value swapped and is now set, so clear error and exception
 302                 x._state._status.set_have_error(false).set_have_exception(false);
 303               }
 304               else
 305               {
 306                 // We know the value swapped and is now unset, so set error
 307                 x._state._status.set_have_error(true);
 308                 // TODO: Should I default construct reset _error? It's guaranteed default constructible.
 309               }
 310             }
 311           };
 312           check(a);
 313           check(b);
 314         }
 315         throw;
 316       }
 317     }
 318   };
 319 #endif
 320
 321 }  // namespace detail
 322 BOOST_OUTCOME_V2_NAMESPACE_END
 323
 324 #endif