impl/conversion.hpp
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impl/conversion.hpp
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| 1 | // | |
| 2 | // Copyright (c) 2020 Krystian Stasiowski (sdkrystian@gmail.com) | |
| 3 | // Copyright (c) 2022 Dmitry Arkhipov (grisumbras@yandex.ru) | |
| 4 | // | |
| 5 | // Distributed under the Boost Software License, Version 1.0. (See accompanying | |
| 6 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | |
| 7 | // | |
| 8 | // Official repository: https://github.com/boostorg/json | |
| 9 | // | |
| 10 | ||
| 11 | #ifndef BOOST_JSON_IMPL_CONVERSION_HPP | |
| 12 | #define BOOST_JSON_IMPL_CONVERSION_HPP | |
| 13 | ||
| 14 | #include <boost/json/fwd.hpp> | |
| 15 | #include <boost/json/value.hpp> | |
| 16 | #include <boost/json/string_view.hpp> | |
| 17 | #include <boost/describe/enumerators.hpp> | |
| 18 | #include <boost/describe/members.hpp> | |
| 19 | #include <boost/describe/bases.hpp> | |
| 20 | #include <boost/mp11/algorithm.hpp> | |
| 21 | #include <boost/mp11/utility.hpp> | |
| 22 | #include <boost/system/result.hpp> | |
| 23 | ||
| 24 | #include <iterator> | |
| 25 | #include <tuple> | |
| 26 | #include <utility> | |
| 27 | #ifndef BOOST_NO_CXX17_HDR_VARIANT | |
| 28 | # include <variant> | |
| 29 | #endif // BOOST_NO_CXX17_HDR_VARIANT | |
| 30 | ||
| 31 | namespace boost { | |
| 32 | namespace json { | |
| 33 | namespace detail { | |
| 34 | ||
| 35 | struct no_context | |
| 36 | {}; | |
| 37 | ||
| 38 | #ifdef __cpp_lib_nonmember_container_access | |
| 39 | using std::size; | |
| 40 | #endif | |
| 41 | ||
| 42 | template<std::size_t I, class T> | |
| 43 | using tuple_element_t = typename std::tuple_element<I, T>::type; | |
| 44 | ||
| 45 | template<class T> | |
| 46 | using iterator_type = decltype(std::begin(std::declval<T&>())); | |
| 47 | template<class T> | |
| 48 | using iterator_traits = std::iterator_traits< iterator_type<T> >; | |
| 49 | ||
| 50 | template<class T> | |
| 51 | using value_type = typename iterator_traits<T>::value_type; | |
| 52 | template<class T> | |
| 53 | using mapped_type = tuple_element_t< 1, value_type<T> >; | |
| 54 | ||
| 55 | // had to make the metafunction always succeeding in order to make it work | |
| 56 | // with msvc 14.0 | |
| 57 | template<class T> | |
| 58 | using key_type_helper = tuple_element_t< 0, value_type<T> >; | |
| 59 | template<class T> | |
| 60 | using key_type = mp11::mp_eval_or< | |
| 61 | void, | |
| 62 | key_type_helper, | |
| 63 | T>; | |
| 64 | ||
| 65 | template<class T> | |
| 66 | using are_begin_and_end_same = std::is_same< | |
| 67 | iterator_type<T>, | |
| 68 | decltype(std::end(std::declval<T&>()))>; | |
| 69 | ||
| 70 | // msvc 14.0 gets confused when std::is_same is used directly | |
| 71 | template<class A, class B> | |
| 72 | using is_same_msvc_140 = std::is_same<A, B>; | |
| 73 | template<class T> | |
| 74 | using is_its_own_value = is_same_msvc_140<value_type<T>, T>; | |
| 75 | ||
| 76 | template<class T> | |
| 77 | using not_its_own_value = mp11::mp_not< is_its_own_value<T> >; | |
| 78 | ||
| 79 | template<class T> | |
| 80 | using begin_iterator_category = typename std::iterator_traits< | |
| 81 | iterator_type<T>>::iterator_category; | |
| 82 | ||
| 83 | template<class T> | |
| 84 | using has_positive_tuple_size = mp11::mp_bool< | |
| 85 | (std::tuple_size<T>::value > 0) >; | |
| 86 | ||
| 87 | template<class T> | |
| 88 | using has_unique_keys = has_positive_tuple_size<decltype( | |
| 89 | std::declval<T&>().emplace( | |
| 90 | std::declval<value_type<T>>()))>; | |
| 91 | ||
| 92 | template<class T> | |
| 93 | using has_string_type = std::is_same< | |
| 94 | typename T::string_type, std::basic_string<typename T::value_type> >; | |
| 95 | ||
| 96 | template<class T> | |
| 97 | struct is_value_type_pair_helper : std::false_type | |
| 98 | { }; | |
| 99 | template<class T1, class T2> | |
| 100 | struct is_value_type_pair_helper<std::pair<T1, T2>> : std::true_type | |
| 101 | { }; | |
| 102 | template<class T> | |
| 103 | using is_value_type_pair = is_value_type_pair_helper<value_type<T>>; | |
| 104 | ||
| 105 | template<class T> | |
| 106 | using has_size_member_helper | |
| 107 | = std::is_convertible<decltype(std::declval<T&>().size()), std::size_t>; | |
| 108 | template<class T> | |
| 109 | using has_size_member = mp11::mp_valid_and_true<has_size_member_helper, T>; | |
| 110 | template<class T> | |
| 111 | using has_free_size_helper | |
| 112 | = std::is_convertible< | |
| 113 | decltype(size(std::declval<T const&>())), | |
| 114 | std::size_t>; | |
| 115 | template<class T> | |
| 116 | using has_free_size = mp11::mp_valid_and_true<has_free_size_helper, T>; | |
| 117 | template<class T> | |
| 118 | using size_implementation = mp11::mp_cond< | |
| 119 | has_size_member<T>, mp11::mp_int<3>, | |
| 120 | has_free_size<T>, mp11::mp_int<2>, | |
| 121 | std::is_array<T>, mp11::mp_int<1>, | |
| 122 | mp11::mp_true, mp11::mp_int<0>>; | |
| 123 | ||
| 124 | template<class T> | |
| 125 | std::size_t | |
| 126 | 155 | try_size(T&& cont, mp11::mp_int<3>) |
| 127 | { | |
| 128 | 155 | return cont.size(); |
| 129 | } | |
| 130 | ||
| 131 | template<class T> | |
| 132 | std::size_t | |
| 133 | 1 | try_size(T& cont, mp11::mp_int<2>) |
| 134 | { | |
| 135 | 1 | return size(cont); |
| 136 | } | |
| 137 | ||
| 138 | template<class T, std::size_t N> | |
| 139 | std::size_t | |
| 140 | 1 | try_size(T(&)[N], mp11::mp_int<1>) |
| 141 | { | |
| 142 | 1 | return N; |
| 143 | } | |
| 144 | ||
| 145 | template<class T> | |
| 146 | std::size_t | |
| 147 | 7 | try_size(T&, mp11::mp_int<0>) |
| 148 | { | |
| 149 | 7 | return 0; |
| 150 | } | |
| 151 | ||
| 152 | template<class T> | |
| 153 | using has_push_back_helper | |
| 154 | = decltype(std::declval<T&>().push_back(std::declval<value_type<T>>())); | |
| 155 | template<class T> | |
| 156 | using has_push_back = mp11::mp_valid<has_push_back_helper, T>; | |
| 157 | template<class T> | |
| 158 | using inserter_implementation = mp11::mp_cond< | |
| 159 | is_tuple_like<T>, mp11::mp_int<2>, | |
| 160 | has_push_back<T>, mp11::mp_int<1>, | |
| 161 | mp11::mp_true, mp11::mp_int<0>>; | |
| 162 | ||
| 163 | template<class T> | |
| 164 | iterator_type<T> | |
| 165 | 56 | inserter( |
| 166 | T& target, | |
| 167 | mp11::mp_int<2>) | |
| 168 | { | |
| 169 | 56 | return target.begin(); |
| 170 | } | |
| 171 | ||
| 172 | template<class T> | |
| 173 | std::back_insert_iterator<T> | |
| 174 | 590 | inserter( |
| 175 | T& target, | |
| 176 | mp11::mp_int<1>) | |
| 177 | { | |
| 178 | 590 | return std::back_inserter(target); |
| 179 | } | |
| 180 | ||
| 181 | template<class T> | |
| 182 | std::insert_iterator<T> | |
| 183 | 72 | inserter( |
| 184 | T& target, | |
| 185 | mp11::mp_int<0>) | |
| 186 | { | |
| 187 | 72 | return std::inserter( target, target.end() ); |
| 188 | } | |
| 189 | ||
| 190 | using value_from_conversion = mp11::mp_true; | |
| 191 | using value_to_conversion = mp11::mp_false; | |
| 192 | ||
| 193 | struct user_conversion_tag { }; | |
| 194 | struct context_conversion_tag : user_conversion_tag { }; | |
| 195 | struct full_context_conversion_tag : context_conversion_tag { }; | |
| 196 | struct native_conversion_tag { }; | |
| 197 | struct value_conversion_tag : native_conversion_tag { }; | |
| 198 | struct object_conversion_tag : native_conversion_tag { }; | |
| 199 | struct array_conversion_tag : native_conversion_tag { }; | |
| 200 | struct string_conversion_tag : native_conversion_tag { }; | |
| 201 | struct bool_conversion_tag : native_conversion_tag { }; | |
| 202 | struct number_conversion_tag : native_conversion_tag { }; | |
| 203 | struct integral_conversion_tag : number_conversion_tag { }; | |
| 204 | struct floating_point_conversion_tag : number_conversion_tag { }; | |
| 205 | struct null_like_conversion_tag { }; | |
| 206 | struct string_like_conversion_tag { }; | |
| 207 | struct map_like_conversion_tag { }; | |
| 208 | struct path_conversion_tag { }; | |
| 209 | struct sequence_conversion_tag { }; | |
| 210 | struct tuple_conversion_tag { }; | |
| 211 | struct described_class_conversion_tag { }; | |
| 212 | struct described_enum_conversion_tag { }; | |
| 213 | struct variant_conversion_tag { }; | |
| 214 | struct optional_conversion_tag { }; | |
| 215 | struct no_conversion_tag { }; | |
| 216 | ||
| 217 | template<class... Args> | |
| 218 | using supports_tag_invoke = decltype(tag_invoke( std::declval<Args>()... )); | |
| 219 | ||
| 220 | template<class T> | |
| 221 | using has_user_conversion_from_impl = supports_tag_invoke< | |
| 222 | value_from_tag, value&, T&& >; | |
| 223 | template<class T> | |
| 224 | using has_user_conversion_to_impl = supports_tag_invoke< | |
| 225 | value_to_tag<T>, value const& >; | |
| 226 | template<class T> | |
| 227 | using has_nonthrowing_user_conversion_to_impl = supports_tag_invoke< | |
| 228 | try_value_to_tag<T>, value const& >; | |
| 229 | template< class T, class Dir > | |
| 230 | using has_user_conversion1 = mp11::mp_if< | |
| 231 | std::is_same<Dir, value_from_conversion>, | |
| 232 | mp11::mp_valid<has_user_conversion_from_impl, T>, | |
| 233 | mp11::mp_or< | |
| 234 | mp11::mp_valid<has_user_conversion_to_impl, T>, | |
| 235 | mp11::mp_valid<has_nonthrowing_user_conversion_to_impl, T>>>; | |
| 236 | ||
| 237 | template< class Ctx, class T > | |
| 238 | using has_context_conversion_from_impl = supports_tag_invoke< | |
| 239 | value_from_tag, value&, T&&, Ctx const& >; | |
| 240 | template< class Ctx, class T > | |
| 241 | using has_context_conversion_to_impl = supports_tag_invoke< | |
| 242 | value_to_tag<T>, value const&, Ctx const& >; | |
| 243 | template< class Ctx, class T > | |
| 244 | using has_nonthrowing_context_conversion_to_impl = supports_tag_invoke< | |
| 245 | try_value_to_tag<T>, value const&, Ctx const& >; | |
| 246 | template< class Ctx, class T, class Dir > | |
| 247 | using has_user_conversion2 = mp11::mp_if< | |
| 248 | std::is_same<Dir, value_from_conversion>, | |
| 249 | mp11::mp_valid<has_context_conversion_from_impl, Ctx, T>, | |
| 250 | mp11::mp_or< | |
| 251 | mp11::mp_valid<has_context_conversion_to_impl, Ctx, T>, | |
| 252 | mp11::mp_valid<has_nonthrowing_context_conversion_to_impl, Ctx, T>>>; | |
| 253 | ||
| 254 | template< class Ctx, class T > | |
| 255 | using has_full_context_conversion_from_impl = supports_tag_invoke< | |
| 256 | value_from_tag, value&, T&&, Ctx const&, Ctx const& >; | |
| 257 | template< class Ctx, class T > | |
| 258 | using has_full_context_conversion_to_impl = supports_tag_invoke< | |
| 259 | value_to_tag<T>, value const&, Ctx const&, Ctx const& >; | |
| 260 | template< class Ctx, class T > | |
| 261 | using has_nonthrowing_full_context_conversion_to_impl = supports_tag_invoke< | |
| 262 | try_value_to_tag<T>, value const&, Ctx const&, Ctx const& >; | |
| 263 | template< class Ctx, class T, class Dir > | |
| 264 | using has_user_conversion3 = mp11::mp_if< | |
| 265 | std::is_same<Dir, value_from_conversion>, | |
| 266 | mp11::mp_valid<has_full_context_conversion_from_impl, Ctx, T>, | |
| 267 | mp11::mp_or< | |
| 268 | mp11::mp_valid<has_full_context_conversion_to_impl, Ctx, T>, | |
| 269 | mp11::mp_valid< | |
| 270 | has_nonthrowing_full_context_conversion_to_impl, Ctx, T>>>; | |
| 271 | ||
| 272 | template< class T > | |
| 273 | using described_non_public_members = describe::describe_members< | |
| 274 | T, describe::mod_private | describe::mod_protected>; | |
| 275 | template< class T > | |
| 276 | using described_bases = describe::describe_bases< | |
| 277 | T, describe::mod_any_access>; | |
| 278 | ||
| 279 | #if defined(BOOST_MSVC) && BOOST_MSVC < 1920 | |
| 280 | ||
| 281 | template< class T > | |
| 282 | struct described_member_t_impl; | |
| 283 | ||
| 284 | template< class T, class C > | |
| 285 | struct described_member_t_impl<T C::*> | |
| 286 | { | |
| 287 | using type = T; | |
| 288 | }; | |
| 289 | ||
| 290 | template< class T, class D > | |
| 291 | using described_member_t = remove_cvref< | |
| 292 | typename described_member_t_impl< | |
| 293 | remove_cvref<decltype(D::pointer)> >::type>; | |
| 294 | ||
| 295 | #else | |
| 296 | ||
| 297 | template< class T, class D > | |
| 298 | using described_member_t = remove_cvref<decltype( | |
| 299 | std::declval<T&>().* D::pointer )>; | |
| 300 | ||
| 301 | #endif | |
| 302 | ||
| 303 | template< class T > | |
| 304 | using described_members = describe::describe_members< | |
| 305 | T, describe::mod_any_access | describe::mod_inherited>; | |
| 306 | ||
| 307 | // user conversion (via tag_invoke) | |
| 308 | template< class Ctx, class T, class Dir > | |
| 309 | using user_conversion_category = mp11::mp_cond< | |
| 310 | has_user_conversion3<Ctx, T, Dir>, full_context_conversion_tag, | |
| 311 | has_user_conversion2<Ctx, T, Dir>, context_conversion_tag, | |
| 312 | has_user_conversion1<T, Dir>, user_conversion_tag>; | |
| 313 | ||
| 314 | // native conversions (constructors and member functions of value) | |
| 315 | template< class T > | |
| 316 | using native_conversion_category = mp11::mp_cond< | |
| 317 | std::is_same<T, value>, value_conversion_tag, | |
| 318 | std::is_same<T, array>, array_conversion_tag, | |
| 319 | std::is_same<T, object>, object_conversion_tag, | |
| 320 | std::is_same<T, string>, string_conversion_tag>; | |
| 321 | ||
| 322 | // generic conversions | |
| 323 | template< class T, class Ctx > | |
| 324 | using generic_conversion_category = mp11::mp_cond< | |
| 325 | std::is_same<T, bool>, bool_conversion_tag, | |
| 326 | std::is_integral<T>, integral_conversion_tag, | |
| 327 | std::is_floating_point<T>, floating_point_conversion_tag, | |
| 328 | is_null_like<T>, null_like_conversion_tag, | |
| 329 | is_string_like<T>, string_like_conversion_tag, | |
| 330 | is_map_like<T, Ctx>, map_like_conversion_tag, | |
| 331 | is_sequence_like<T>, sequence_conversion_tag, | |
| 332 | is_tuple_like<T>, tuple_conversion_tag, | |
| 333 | is_described_class<T>, described_class_conversion_tag, | |
| 334 | is_described_enum<T>, described_enum_conversion_tag, | |
| 335 | is_variant_like<T>, variant_conversion_tag, | |
| 336 | is_optional_like<T>, optional_conversion_tag, | |
| 337 | is_path_like<T>, path_conversion_tag, | |
| 338 | // failed to find a suitable implementation | |
| 339 | mp11::mp_true, no_conversion_tag>; | |
| 340 | ||
| 341 | template< class T > | |
| 342 | using nested_type = typename T::type; | |
| 343 | template< class T1, class T2 > | |
| 344 | using conversion_category_helper = mp11::mp_eval_if_not< | |
| 345 | std::is_same<detail::no_conversion_tag, T1>, | |
| 346 | T1, | |
| 347 | mp11::mp_eval_or_q, T1, mp11::mp_quote<nested_type>, T2>; | |
| 348 | ||
| 349 | template< class Ctx > | |
| 350 | using fix_context = mp11::mp_if< std::is_same<Ctx, no_context>, void, Ctx>; | |
| 351 | ||
| 352 | template<class T, class Ctx> | |
| 353 | using representation_or_void = mp11::mp_eval_or<void, represent_as_t, T, Ctx>; | |
| 354 | ||
| 355 | template< class U > | |
| 356 | using is_not_void = mp11::mp_bool< !std::is_same<void, U>::value >; | |
| 357 | ||
| 358 | template< class T, class Ctxs > | |
| 359 | struct representation_helper | |
| 360 | { | |
| 361 | using size = mp11::mp_size<Ctxs>; | |
| 362 | ||
| 363 | template< class I > | |
| 364 | using exists = mp11::mp_less<I, size>; | |
| 365 | ||
| 366 | template< class Ctx > | |
| 367 | using step = representation_or_void<T, Ctx>; | |
| 368 | using reps = mp11::mp_transform<step, Ctxs>; | |
| 369 | using r_index = mp11::mp_find_if< reps, is_not_void >; | |
| 370 | ||
| 371 | using type = mp11::mp_eval_if< | |
| 372 | mp11::mp_not< exists<r_index> >, | |
| 373 | T, | |
| 374 | mp11::mp_at, reps, r_index>; | |
| 375 | }; | |
| 376 | ||
| 377 | template< class T, class Ctx > | |
| 378 | struct conversion_representation_impl | |
| 379 | : representation_helper< T, mp11::mp_list<Ctx, void> > | |
| 380 | {}; | |
| 381 | ||
| 382 | template< class T > | |
| 383 | struct conversion_representation_impl<T, no_context> | |
| 384 | : representation_helper< T, mp11::mp_list<void> > | |
| 385 | {}; | |
| 386 | ||
| 387 | template< class T, class... Ctxs > | |
| 388 | struct conversion_representation_impl< T, std::tuple<Ctxs...> > | |
| 389 | : representation_helper< T, mp11::mp_list<remove_cvref<Ctxs>..., void> > | |
| 390 | {}; | |
| 391 | ||
| 392 | template< class T, class Ctx > | |
| 393 | using conversion_representation | |
| 394 | = typename conversion_representation_impl<remove_cvref<T>, Ctx>::type; | |
| 395 | ||
| 396 | template< class Ctx, class T, class Dir > | |
| 397 | struct conversion_attrs | |
| 398 | { | |
| 399 | using representation = conversion_representation<T, Ctx>; | |
| 400 | ||
| 401 | using category = mp11::mp_fold< | |
| 402 | mp11::mp_list< | |
| 403 | mp11::mp_defer<user_conversion_category, Ctx, representation, Dir>, | |
| 404 | mp11::mp_defer<native_conversion_category, representation>, | |
| 405 | mp11::mp_defer<generic_conversion_category, representation, Ctx>>, | |
| 406 | no_conversion_tag, | |
| 407 | conversion_category_helper>; | |
| 408 | }; | |
| 409 | ||
| 410 | template< class T > | |
| 411 | using any_conversion_tag = mp11::mp_not< | |
| 412 | std::is_same< T, no_conversion_tag > >; | |
| 413 | ||
| 414 | template< class Ctx, class T, class Dir > | |
| 415 | using conversion_category = typename conversion_attrs<Ctx, T, Dir>::category; | |
| 416 | ||
| 417 | template< class T, class Dir, class... Ctxs > | |
| 418 | struct conversion_attrs< std::tuple<Ctxs...>, T, Dir > | |
| 419 | { | |
| 420 | using size = mp11::mp_size_t< sizeof...(Ctxs) >; | |
| 421 | using ctxs = mp11::mp_list< remove_cvref<Ctxs>... >; | |
| 422 | ||
| 423 | template< class I > | |
| 424 | using exists = mp11::mp_less<I, size>; | |
| 425 | ||
| 426 | using representation = conversion_representation< T, std::tuple<Ctxs...> >; | |
| 427 | ||
| 428 | using cats = mp11::mp_list< | |
| 429 | conversion_category<remove_cvref<Ctxs>, representation, Dir>... >; | |
| 430 | ||
| 431 | using context2 = mp11::mp_find< cats, full_context_conversion_tag >; | |
| 432 | using context1 = mp11::mp_find< cats, context_conversion_tag >; | |
| 433 | using context0 = mp11::mp_find< cats, user_conversion_tag >; | |
| 434 | using index = mp11::mp_cond< | |
| 435 | exists<context2>, context2, | |
| 436 | exists<context1>, context1, | |
| 437 | exists<context0>, context0, | |
| 438 | mp11::mp_true, mp11::mp_find_if< cats, any_conversion_tag > >; | |
| 439 | using category = mp11::mp_eval_or< | |
| 440 | no_conversion_tag, | |
| 441 | mp11::mp_at, cats, index >; | |
| 442 | }; | |
| 443 | ||
| 444 | template <class T, class Dir> | |
| 445 | using can_convert = mp11::mp_not< | |
| 446 | std::is_same< | |
| 447 | detail::conversion_category<no_context, T, Dir>, | |
| 448 | detail::no_conversion_tag>>; | |
| 449 | ||
| 450 | template<class Impl1, class Impl2> | |
| 451 | using conversion_round_trips_helper = mp11::mp_or< | |
| 452 | std::is_same<Impl1, Impl2>, | |
| 453 | std::is_base_of<user_conversion_tag, Impl1>, | |
| 454 | std::is_base_of<user_conversion_tag, Impl2>>; | |
| 455 | template< class Ctx, class T, class Dir > | |
| 456 | using conversion_round_trips = conversion_round_trips_helper< | |
| 457 | conversion_category<Ctx, T, Dir>, | |
| 458 | conversion_category<Ctx, T, mp11::mp_not<Dir>>>; | |
| 459 | ||
| 460 | template< class T1, class T2 > | |
| 461 | struct copy_cref_helper | |
| 462 | { | |
| 463 | using type = remove_cvref<T2>; | |
| 464 | }; | |
| 465 | template< class T1, class T2 > | |
| 466 | using copy_cref = typename copy_cref_helper< T1, T2 >::type; | |
| 467 | ||
| 468 | template< class T1, class T2 > | |
| 469 | struct copy_cref_helper<T1 const, T2> | |
| 470 | { | |
| 471 | using type = remove_cvref<T2> const; | |
| 472 | }; | |
| 473 | template< class T1, class T2 > | |
| 474 | struct copy_cref_helper<T1&, T2> | |
| 475 | { | |
| 476 | using type = copy_cref<T1, T2>&; | |
| 477 | }; | |
| 478 | template< class T1, class T2 > | |
| 479 | struct copy_cref_helper<T1&&, T2> | |
| 480 | { | |
| 481 | using type = copy_cref<T1, T2>&&; | |
| 482 | }; | |
| 483 | ||
| 484 | template< class Rng, class Traits > | |
| 485 | using forwarded_value_helper = mp11::mp_if< | |
| 486 | std::is_convertible< | |
| 487 | typename Traits::reference, | |
| 488 | copy_cref<Rng, typename Traits::value_type> >, | |
| 489 | copy_cref<Rng, typename Traits::value_type>, | |
| 490 | typename Traits::value_type >; | |
| 491 | ||
| 492 | template< class Rng > | |
| 493 | using forwarded_value = forwarded_value_helper< | |
| 494 | Rng, iterator_traits< Rng > >; | |
| 495 | ||
| 496 | template< class Ctx, class T, class Dir > | |
| 497 | struct supported_context | |
| 498 | { | |
| 499 | using type = Ctx; | |
| 500 | ||
| 501 | static | |
| 502 | type const& | |
| 503 | 32 | get( Ctx const& ctx ) noexcept |
| 504 | { | |
| 505 | 32 | return ctx; |
| 506 | } | |
| 507 | }; | |
| 508 | ||
| 509 | template< class T, class Dir, class... Ctxs > | |
| 510 | struct supported_context< std::tuple<Ctxs...>, T, Dir > | |
| 511 | { | |
| 512 | using Ctx = std::tuple<Ctxs...>; | |
| 513 | using Attrs = conversion_attrs<Ctx, T, Dir>; | |
| 514 | using index = typename Attrs::index; | |
| 515 | using next_supported = supported_context< | |
| 516 | mp11::mp_at< typename Attrs::ctxs, index >, T, Dir >; | |
| 517 | using type = typename next_supported::type; | |
| 518 | ||
| 519 | static | |
| 520 | type const& | |
| 521 | 19 | get( Ctx const& ctx ) noexcept |
| 522 | { | |
| 523 | 19 | return next_supported::get( std::get<index::value>( ctx ) ); |
| 524 | } | |
| 525 | }; | |
| 526 | ||
| 527 | template< class T > | |
| 528 | using value_result_type = typename std::decay< | |
| 529 | decltype( std::declval<T&>().value() )>::type; | |
| 530 | ||
| 531 | template< class T > | |
| 532 | using can_reset = decltype( std::declval<T&>().reset() ); | |
| 533 | ||
| 534 | template< class T > | |
| 535 | using has_valueless_by_exception = | |
| 536 | decltype( std::declval<T const&>().valueless_by_exception() ); | |
| 537 | ||
| 538 | } // namespace detail | |
| 539 | ||
| 540 | template <class T> | |
| 541 | struct result_for<T, value> | |
| 542 | { | |
| 543 | using type = system::result< detail::remove_cvref<T> >; | |
| 544 | }; | |
| 545 | ||
| 546 | template<class T> | |
| 547 | struct is_string_like | |
| 548 | : std::is_convertible<T, string_view> | |
| 549 | { }; | |
| 550 | ||
| 551 | template<class T> | |
| 552 | struct is_path_like | |
| 553 | : mp11::mp_all< | |
| 554 | mp11::mp_valid_and_true<detail::is_its_own_value, T>, | |
| 555 | mp11::mp_valid_and_true<detail::has_string_type, T>> | |
| 556 | { }; | |
| 557 | template<class T> | |
| 558 | struct is_sequence_like | |
| 559 | : mp11::mp_all< | |
| 560 | mp11::mp_valid_and_true<detail::are_begin_and_end_same, T>, | |
| 561 | mp11::mp_valid_and_true<detail::not_its_own_value, T>, | |
| 562 | mp11::mp_valid<detail::begin_iterator_category, T>> | |
| 563 | { }; | |
| 564 | ||
| 565 | template<class T, class Ctx> | |
| 566 | struct is_map_like | |
| 567 | : mp11::mp_all< | |
| 568 | is_sequence_like<T>, | |
| 569 | mp11::mp_valid_and_true<detail::is_value_type_pair, T>, | |
| 570 | is_string_like< | |
| 571 | detail::conversion_representation< | |
| 572 | detail::remove_cvref< detail::key_type<T> >, Ctx>>, | |
| 573 | mp11::mp_valid_and_true<detail::has_unique_keys, T>> | |
| 574 | { }; | |
| 575 | ||
| 576 | template<class T> | |
| 577 | struct is_tuple_like | |
| 578 | : mp11::mp_valid_and_true<detail::has_positive_tuple_size, T> | |
| 579 | { }; | |
| 580 | ||
| 581 | template<> | |
| 582 | struct is_null_like<std::nullptr_t> | |
| 583 | : std::true_type | |
| 584 | { }; | |
| 585 | ||
| 586 | #ifndef BOOST_NO_CXX17_HDR_VARIANT | |
| 587 | template<> | |
| 588 | struct is_null_like<std::monostate> | |
| 589 | : std::true_type | |
| 590 | { }; | |
| 591 | #endif // BOOST_NO_CXX17_HDR_VARIANT | |
| 592 | ||
| 593 | template<class T> | |
| 594 | struct is_described_class | |
| 595 | : mp11::mp_and< | |
| 596 | describe::has_describe_members<T>, | |
| 597 | mp11::mp_not< std::is_union<T> >, | |
| 598 | mp11::mp_empty< | |
| 599 | mp11::mp_eval_or< | |
| 600 | mp11::mp_list<>, detail::described_non_public_members, T>>, | |
| 601 | mp11::mp_empty< | |
| 602 | mp11::mp_eval_or<mp11::mp_list<>, detail::described_bases, T>>> | |
| 603 | { }; | |
| 604 | ||
| 605 | template<class T> | |
| 606 | struct is_described_enum | |
| 607 | : describe::has_describe_enumerators<T> | |
| 608 | { }; | |
| 609 | ||
| 610 | template<class T> | |
| 611 | struct is_variant_like : mp11::mp_valid<detail::has_valueless_by_exception, T> | |
| 612 | { }; | |
| 613 | ||
| 614 | template<class T> | |
| 615 | struct is_optional_like | |
| 616 | : mp11::mp_and< | |
| 617 | mp11::mp_not<std::is_void< | |
| 618 | mp11::mp_eval_or<void, detail::value_result_type, T>>>, | |
| 619 | mp11::mp_valid<detail::can_reset, T>> | |
| 620 | { }; | |
| 621 | ||
| 622 | } // namespace json | |
| 623 | } // namespace boost | |
| 624 | ||
| 625 | #endif // BOOST_JSON_IMPL_CONVERSION_HPP | |
| 626 |