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 | #ifdef __cpp_lib_nonmember_container_access | |
| 36 | using std::size; | |
| 37 | #endif | |
| 38 | ||
| 39 | template<std::size_t I, class T> | |
| 40 | using tuple_element_t = typename std::tuple_element<I, T>::type; | |
| 41 | ||
| 42 | template<class T> | |
| 43 | using iterator_type = decltype(std::begin(std::declval<T&>())); | |
| 44 | template<class T> | |
| 45 | using iterator_traits = std::iterator_traits< iterator_type<T> >; | |
| 46 | ||
| 47 | template<class T> | |
| 48 | using value_type = typename iterator_traits<T>::value_type; | |
| 49 | template<class T> | |
| 50 | using mapped_type = tuple_element_t< 1, value_type<T> >; | |
| 51 | ||
| 52 | // had to make the metafunction always succeeding in order to make it work | |
| 53 | // with msvc 14.0 | |
| 54 | template<class T> | |
| 55 | using key_type_helper = tuple_element_t< 0, value_type<T> >; | |
| 56 | template<class T> | |
| 57 | using key_type = mp11::mp_eval_or< | |
| 58 | void, | |
| 59 | key_type_helper, | |
| 60 | T>; | |
| 61 | ||
| 62 | template<class T> | |
| 63 | using are_begin_and_end_same = std::is_same< | |
| 64 | iterator_type<T>, | |
| 65 | decltype(std::end(std::declval<T&>()))>; | |
| 66 | ||
| 67 | // msvc 14.0 gets confused when std::is_same is used directly | |
| 68 | template<class A, class B> | |
| 69 | using is_same_msvc_140 = std::is_same<A, B>; | |
| 70 | template<class T> | |
| 71 | using is_its_own_value = is_same_msvc_140<value_type<T>, T>; | |
| 72 | ||
| 73 | template<class T> | |
| 74 | using not_its_own_value = mp11::mp_not< is_its_own_value<T> >; | |
| 75 | ||
| 76 | template<class T> | |
| 77 | using begin_iterator_category = typename std::iterator_traits< | |
| 78 | iterator_type<T>>::iterator_category; | |
| 79 | ||
| 80 | template<class T> | |
| 81 | using has_positive_tuple_size = mp11::mp_bool< | |
| 82 | (std::tuple_size<T>::value > 0) >; | |
| 83 | ||
| 84 | template<class T> | |
| 85 | using has_unique_keys = has_positive_tuple_size<decltype( | |
| 86 | std::declval<T&>().emplace( | |
| 87 | std::declval<value_type<T>>()))>; | |
| 88 | ||
| 89 | template<class T> | |
| 90 | using has_string_type = std::is_same< | |
| 91 | typename T::string_type, std::basic_string<typename T::value_type> >; | |
| 92 | ||
| 93 | template<class T> | |
| 94 | struct is_value_type_pair_helper : std::false_type | |
| 95 | { }; | |
| 96 | template<class T1, class T2> | |
| 97 | struct is_value_type_pair_helper<std::pair<T1, T2>> : std::true_type | |
| 98 | { }; | |
| 99 | template<class T> | |
| 100 | using is_value_type_pair = is_value_type_pair_helper<value_type<T>>; | |
| 101 | ||
| 102 | template<class T> | |
| 103 | using has_size_member_helper | |
| 104 | = std::is_convertible<decltype(std::declval<T&>().size()), std::size_t>; | |
| 105 | template<class T> | |
| 106 | using has_size_member = mp11::mp_valid_and_true<has_size_member_helper, T>; | |
| 107 | template<class T> | |
| 108 | using has_free_size_helper | |
| 109 | = std::is_convertible< | |
| 110 | decltype(size(std::declval<T const&>())), | |
| 111 | std::size_t>; | |
| 112 | template<class T> | |
| 113 | using has_free_size = mp11::mp_valid_and_true<has_free_size_helper, T>; | |
| 114 | template<class T> | |
| 115 | using size_implementation = mp11::mp_cond< | |
| 116 | has_size_member<T>, mp11::mp_int<3>, | |
| 117 | has_free_size<T>, mp11::mp_int<2>, | |
| 118 | std::is_array<T>, mp11::mp_int<1>, | |
| 119 | mp11::mp_true, mp11::mp_int<0>>; | |
| 120 | ||
| 121 | template<class T> | |
| 122 | std::size_t | |
| 123 | 138 | try_size(T&& cont, mp11::mp_int<3>) |
| 124 | { | |
| 125 | 138 | return cont.size(); |
| 126 | } | |
| 127 | ||
| 128 | template<class T> | |
| 129 | std::size_t | |
| 130 | 1 | try_size(T& cont, mp11::mp_int<2>) |
| 131 | { | |
| 132 | 1 | return size(cont); |
| 133 | } | |
| 134 | ||
| 135 | template<class T, std::size_t N> | |
| 136 | std::size_t | |
| 137 | 1 | try_size(T(&)[N], mp11::mp_int<1>) |
| 138 | { | |
| 139 | 1 | return N; |
| 140 | } | |
| 141 | ||
| 142 | template<class T> | |
| 143 | std::size_t | |
| 144 | 7 | try_size(T&, mp11::mp_int<0>) |
| 145 | { | |
| 146 | 7 | return 0; |
| 147 | } | |
| 148 | ||
| 149 | template<class T> | |
| 150 | using has_push_back_helper | |
| 151 | = decltype(std::declval<T&>().push_back(std::declval<value_type<T>>())); | |
| 152 | template<class T> | |
| 153 | using has_push_back = mp11::mp_valid<has_push_back_helper, T>; | |
| 154 | template<class T> | |
| 155 | using inserter_implementation = mp11::mp_cond< | |
| 156 | is_tuple_like<T>, mp11::mp_int<2>, | |
| 157 | has_push_back<T>, mp11::mp_int<1>, | |
| 158 | mp11::mp_true, mp11::mp_int<0>>; | |
| 159 | ||
| 160 | template<class T> | |
| 161 | iterator_type<T> | |
| 162 | 56 | inserter( |
| 163 | T& target, | |
| 164 | mp11::mp_int<2>) | |
| 165 | { | |
| 166 | 56 | return target.begin(); |
| 167 | } | |
| 168 | ||
| 169 | template<class T> | |
| 170 | std::back_insert_iterator<T> | |
| 171 | 569 | inserter( |
| 172 | T& target, | |
| 173 | mp11::mp_int<1>) | |
| 174 | { | |
| 175 | 569 | return std::back_inserter(target); |
| 176 | } | |
| 177 | ||
| 178 | template<class T> | |
| 179 | std::insert_iterator<T> | |
| 180 | 62 | inserter( |
| 181 | T& target, | |
| 182 | mp11::mp_int<0>) | |
| 183 | { | |
| 184 | 62 | return std::inserter( target, target.end() ); |
| 185 | } | |
| 186 | ||
| 187 | using value_from_conversion = mp11::mp_true; | |
| 188 | using value_to_conversion = mp11::mp_false; | |
| 189 | ||
| 190 | struct user_conversion_tag { }; | |
| 191 | struct context_conversion_tag : user_conversion_tag { }; | |
| 192 | struct full_context_conversion_tag : context_conversion_tag { }; | |
| 193 | struct native_conversion_tag { }; | |
| 194 | struct value_conversion_tag : native_conversion_tag { }; | |
| 195 | struct object_conversion_tag : native_conversion_tag { }; | |
| 196 | struct array_conversion_tag : native_conversion_tag { }; | |
| 197 | struct string_conversion_tag : native_conversion_tag { }; | |
| 198 | struct bool_conversion_tag : native_conversion_tag { }; | |
| 199 | struct number_conversion_tag : native_conversion_tag { }; | |
| 200 | struct integral_conversion_tag : number_conversion_tag { }; | |
| 201 | struct floating_point_conversion_tag : number_conversion_tag { }; | |
| 202 | struct null_like_conversion_tag { }; | |
| 203 | struct string_like_conversion_tag { }; | |
| 204 | struct map_like_conversion_tag { }; | |
| 205 | struct path_conversion_tag { }; | |
| 206 | struct sequence_conversion_tag { }; | |
| 207 | struct tuple_conversion_tag { }; | |
| 208 | struct described_class_conversion_tag { }; | |
| 209 | struct described_enum_conversion_tag { }; | |
| 210 | struct variant_conversion_tag { }; | |
| 211 | struct optional_conversion_tag { }; | |
| 212 | struct no_conversion_tag { }; | |
| 213 | ||
| 214 | template<class... Args> | |
| 215 | using supports_tag_invoke = decltype(tag_invoke( std::declval<Args>()... )); | |
| 216 | ||
| 217 | template<class T> | |
| 218 | using has_user_conversion_from_impl = supports_tag_invoke< | |
| 219 | value_from_tag, value&, T&& >; | |
| 220 | template<class T> | |
| 221 | using has_user_conversion_to_impl = supports_tag_invoke< | |
| 222 | value_to_tag<T>, value const& >; | |
| 223 | template<class T> | |
| 224 | using has_nonthrowing_user_conversion_to_impl = supports_tag_invoke< | |
| 225 | try_value_to_tag<T>, value const& >; | |
| 226 | template< class T, class Dir > | |
| 227 | using has_user_conversion1 = mp11::mp_if< | |
| 228 | std::is_same<Dir, value_from_conversion>, | |
| 229 | mp11::mp_valid<has_user_conversion_from_impl, T>, | |
| 230 | mp11::mp_or< | |
| 231 | mp11::mp_valid<has_user_conversion_to_impl, T>, | |
| 232 | mp11::mp_valid<has_nonthrowing_user_conversion_to_impl, T>>>; | |
| 233 | ||
| 234 | template< class Ctx, class T > | |
| 235 | using has_context_conversion_from_impl = supports_tag_invoke< | |
| 236 | value_from_tag, value&, T&&, Ctx const& >; | |
| 237 | template< class Ctx, class T > | |
| 238 | using has_context_conversion_to_impl = supports_tag_invoke< | |
| 239 | value_to_tag<T>, value const&, Ctx const& >; | |
| 240 | template< class Ctx, class T > | |
| 241 | using has_nonthrowing_context_conversion_to_impl = supports_tag_invoke< | |
| 242 | try_value_to_tag<T>, value const&, Ctx const& >; | |
| 243 | template< class Ctx, class T, class Dir > | |
| 244 | using has_user_conversion2 = mp11::mp_if< | |
| 245 | std::is_same<Dir, value_from_conversion>, | |
| 246 | mp11::mp_valid<has_context_conversion_from_impl, Ctx, T>, | |
| 247 | mp11::mp_or< | |
| 248 | mp11::mp_valid<has_context_conversion_to_impl, Ctx, T>, | |
| 249 | mp11::mp_valid<has_nonthrowing_context_conversion_to_impl, Ctx, T>>>; | |
| 250 | ||
| 251 | template< class Ctx, class T > | |
| 252 | using has_full_context_conversion_from_impl = supports_tag_invoke< | |
| 253 | value_from_tag, value&, T&&, Ctx const&, Ctx const& >; | |
| 254 | template< class Ctx, class T > | |
| 255 | using has_full_context_conversion_to_impl = supports_tag_invoke< | |
| 256 | value_to_tag<T>, value const&, Ctx const&, Ctx const& >; | |
| 257 | template< class Ctx, class T > | |
| 258 | using has_nonthrowing_full_context_conversion_to_impl = supports_tag_invoke< | |
| 259 | try_value_to_tag<T>, value const&, Ctx const&, Ctx const& >; | |
| 260 | template< class Ctx, class T, class Dir > | |
| 261 | using has_user_conversion3 = mp11::mp_if< | |
| 262 | std::is_same<Dir, value_from_conversion>, | |
| 263 | mp11::mp_valid<has_full_context_conversion_from_impl, Ctx, T>, | |
| 264 | mp11::mp_or< | |
| 265 | mp11::mp_valid<has_full_context_conversion_to_impl, Ctx, T>, | |
| 266 | mp11::mp_valid< | |
| 267 | has_nonthrowing_full_context_conversion_to_impl, Ctx, T>>>; | |
| 268 | ||
| 269 | template< class T > | |
| 270 | using described_non_public_members = describe::describe_members< | |
| 271 | T, | |
| 272 | describe::mod_private | |
| 273 | | describe::mod_protected | |
| 274 | | boost::describe::mod_inherited>; | |
| 275 | ||
| 276 | #if defined(BOOST_MSVC) && BOOST_MSVC < 1920 | |
| 277 | ||
| 278 | template< class T > | |
| 279 | struct described_member_t_impl; | |
| 280 | ||
| 281 | template< class T, class C > | |
| 282 | struct described_member_t_impl<T C::*> | |
| 283 | { | |
| 284 | using type = T; | |
| 285 | }; | |
| 286 | ||
| 287 | template< class T, class D > | |
| 288 | using described_member_t = remove_cvref< | |
| 289 | typename described_member_t_impl< | |
| 290 | remove_cvref<decltype(D::pointer)> >::type>; | |
| 291 | ||
| 292 | #else | |
| 293 | ||
| 294 | template< class T, class D > | |
| 295 | using described_member_t = remove_cvref<decltype( | |
| 296 | std::declval<T&>().* D::pointer )>; | |
| 297 | ||
| 298 | #endif | |
| 299 | ||
| 300 | template< class T > | |
| 301 | using described_members = describe::describe_members< | |
| 302 | T, describe::mod_any_access | describe::mod_inherited>; | |
| 303 | ||
| 304 | #ifdef BOOST_DESCRIBE_CXX14 | |
| 305 | ||
| 306 | constexpr | |
| 307 | bool | |
| 308 | compare_strings(char const* l, char const* r) | |
| 309 | { | |
| 310 | #if defined(_MSC_VER) && (_MSC_VER <= 1900) && !defined(__clang__) | |
| 311 | return *l == *r && ( (*l == 0) | compare_strings(l + 1, r + 1) ); | |
| 312 | #else | |
| 313 | do | |
| 314 | { | |
| 315 | if( *l != *r ) | |
| 316 | return false; | |
| 317 | if( *l == 0 ) | |
| 318 | return true; | |
| 319 | ++l; | |
| 320 | ++r; | |
| 321 | } while(true); | |
| 322 | #endif | |
| 323 | } | |
| 324 | ||
| 325 | template< class L, class R > | |
| 326 | struct equal_member_names | |
| 327 | : mp11::mp_bool< compare_strings(L::name, R::name) > | |
| 328 | {}; | |
| 329 | ||
| 330 | template< class T > | |
| 331 | using uniquely_named_members = mp11::mp_same< | |
| 332 | mp11::mp_unique_if< described_members<T>, equal_member_names >, | |
| 333 | described_members<T> >; | |
| 334 | ||
| 335 | #else | |
| 336 | ||
| 337 | // we only check this in C++14, but the template should exist nevertheless | |
| 338 | template< class T > | |
| 339 | using uniquely_named_members = std::true_type; | |
| 340 | ||
| 341 | #endif // BOOST_DESCRIBE_CXX14 | |
| 342 | ||
| 343 | // user conversion (via tag_invoke) | |
| 344 | template< class Ctx, class T, class Dir > | |
| 345 | using user_conversion_category = mp11::mp_cond< | |
| 346 | has_user_conversion3<Ctx, T, Dir>, full_context_conversion_tag, | |
| 347 | has_user_conversion2<Ctx, T, Dir>, context_conversion_tag, | |
| 348 | has_user_conversion1<T, Dir>, user_conversion_tag>; | |
| 349 | ||
| 350 | // native conversions (constructors and member functions of value) | |
| 351 | template< class T > | |
| 352 | using native_conversion_category = mp11::mp_cond< | |
| 353 | std::is_same<T, value>, value_conversion_tag, | |
| 354 | std::is_same<T, array>, array_conversion_tag, | |
| 355 | std::is_same<T, object>, object_conversion_tag, | |
| 356 | std::is_same<T, string>, string_conversion_tag>; | |
| 357 | ||
| 358 | // generic conversions | |
| 359 | template< class T > | |
| 360 | using generic_conversion_category = mp11::mp_cond< | |
| 361 | std::is_same<T, bool>, bool_conversion_tag, | |
| 362 | std::is_integral<T>, integral_conversion_tag, | |
| 363 | std::is_floating_point<T>, floating_point_conversion_tag, | |
| 364 | is_null_like<T>, null_like_conversion_tag, | |
| 365 | is_string_like<T>, string_like_conversion_tag, | |
| 366 | is_variant_like<T>, variant_conversion_tag, | |
| 367 | is_optional_like<T>, optional_conversion_tag, | |
| 368 | is_map_like<T>, map_like_conversion_tag, | |
| 369 | is_sequence_like<T>, sequence_conversion_tag, | |
| 370 | is_tuple_like<T>, tuple_conversion_tag, | |
| 371 | is_described_class<T>, described_class_conversion_tag, | |
| 372 | is_described_enum<T>, described_enum_conversion_tag, | |
| 373 | is_path_like<T>, path_conversion_tag, | |
| 374 | // failed to find a suitable implementation | |
| 375 | mp11::mp_true, no_conversion_tag>; | |
| 376 | ||
| 377 | template< class T > | |
| 378 | using nested_type = typename T::type; | |
| 379 | template< class T1, class T2 > | |
| 380 | using conversion_category_impl_helper = mp11::mp_eval_if_not< | |
| 381 | std::is_same<detail::no_conversion_tag, T1>, | |
| 382 | T1, | |
| 383 | mp11::mp_eval_or_q, T1, mp11::mp_quote<nested_type>, T2>; | |
| 384 | template< class Ctx, class T, class Dir > | |
| 385 | struct conversion_category_impl | |
| 386 | { | |
| 387 | using type = mp11::mp_fold< | |
| 388 | mp11::mp_list< | |
| 389 | mp11::mp_defer<user_conversion_category, Ctx, T, Dir>, | |
| 390 | mp11::mp_defer<native_conversion_category, T>, | |
| 391 | mp11::mp_defer<generic_conversion_category, T>>, | |
| 392 | no_conversion_tag, | |
| 393 | conversion_category_impl_helper>; | |
| 394 | }; | |
| 395 | template< class Ctx, class T, class Dir > | |
| 396 | using conversion_category = | |
| 397 | typename conversion_category_impl< Ctx, T, Dir >::type; | |
| 398 | ||
| 399 | template< class T > | |
| 400 | using any_conversion_tag = mp11::mp_not< | |
| 401 | std::is_same< T, no_conversion_tag > >; | |
| 402 | ||
| 403 | template< class T, class Dir, class... Ctxs > | |
| 404 | struct conversion_category_impl< std::tuple<Ctxs...>, T, Dir > | |
| 405 | { | |
| 406 | using ctxs = mp11::mp_list< remove_cvref<Ctxs>... >; | |
| 407 | using cats = mp11::mp_list< | |
| 408 | conversion_category<remove_cvref<Ctxs>, T, Dir>... >; | |
| 409 | ||
| 410 | template< class I > | |
| 411 | using exists = mp11::mp_less< I, mp11::mp_size<cats> >; | |
| 412 | ||
| 413 | using context2 = mp11::mp_find< cats, full_context_conversion_tag >; | |
| 414 | using context1 = mp11::mp_find< cats, context_conversion_tag >; | |
| 415 | using context0 = mp11::mp_find< cats, user_conversion_tag >; | |
| 416 | using index = mp11::mp_cond< | |
| 417 | exists<context2>, context2, | |
| 418 | exists<context1>, context1, | |
| 419 | exists<context0>, context0, | |
| 420 | mp11::mp_true, mp11::mp_find_if< cats, any_conversion_tag > >; | |
| 421 | using type = mp11::mp_eval_or< | |
| 422 | no_conversion_tag, | |
| 423 | mp11::mp_at, cats, index >; | |
| 424 | }; | |
| 425 | ||
| 426 | struct no_context | |
| 427 | {}; | |
| 428 | ||
| 429 | template <class T, class Dir> | |
| 430 | using can_convert = mp11::mp_not< | |
| 431 | std::is_same< | |
| 432 | detail::conversion_category<no_context, T, Dir>, | |
| 433 | detail::no_conversion_tag>>; | |
| 434 | ||
| 435 | template<class Impl1, class Impl2> | |
| 436 | using conversion_round_trips_helper = mp11::mp_or< | |
| 437 | std::is_same<Impl1, Impl2>, | |
| 438 | std::is_base_of<user_conversion_tag, Impl1>, | |
| 439 | std::is_base_of<user_conversion_tag, Impl2>>; | |
| 440 | template< class Ctx, class T, class Dir > | |
| 441 | using conversion_round_trips = conversion_round_trips_helper< | |
| 442 | conversion_category<Ctx, T, Dir>, | |
| 443 | conversion_category<Ctx, T, mp11::mp_not<Dir>>>; | |
| 444 | ||
| 445 | template< class T1, class T2 > | |
| 446 | struct copy_cref_helper | |
| 447 | { | |
| 448 | using type = remove_cvref<T2>; | |
| 449 | }; | |
| 450 | template< class T1, class T2 > | |
| 451 | using copy_cref = typename copy_cref_helper< T1, T2 >::type; | |
| 452 | ||
| 453 | template< class T1, class T2 > | |
| 454 | struct copy_cref_helper<T1 const, T2> | |
| 455 | { | |
| 456 | using type = remove_cvref<T2> const; | |
| 457 | }; | |
| 458 | template< class T1, class T2 > | |
| 459 | struct copy_cref_helper<T1&, T2> | |
| 460 | { | |
| 461 | using type = copy_cref<T1, T2>&; | |
| 462 | }; | |
| 463 | template< class T1, class T2 > | |
| 464 | struct copy_cref_helper<T1&&, T2> | |
| 465 | { | |
| 466 | using type = copy_cref<T1, T2>&&; | |
| 467 | }; | |
| 468 | ||
| 469 | template< class Rng, class Traits > | |
| 470 | using forwarded_value_helper = mp11::mp_if< | |
| 471 | std::is_convertible< | |
| 472 | typename Traits::reference, | |
| 473 | copy_cref<Rng, typename Traits::value_type> >, | |
| 474 | copy_cref<Rng, typename Traits::value_type>, | |
| 475 | typename Traits::value_type >; | |
| 476 | ||
| 477 | template< class Rng > | |
| 478 | using forwarded_value = forwarded_value_helper< | |
| 479 | Rng, iterator_traits< Rng > >; | |
| 480 | ||
| 481 | template< class Ctx, class T, class Dir > | |
| 482 | struct supported_context | |
| 483 | { | |
| 484 | using type = Ctx; | |
| 485 | ||
| 486 | static | |
| 487 | type const& | |
| 488 | 32 | get( Ctx const& ctx ) noexcept |
| 489 | { | |
| 490 | 32 | return ctx; |
| 491 | } | |
| 492 | }; | |
| 493 | ||
| 494 | template< class T, class Dir, class... Ctxs > | |
| 495 | struct supported_context< std::tuple<Ctxs...>, T, Dir > | |
| 496 | { | |
| 497 | using Ctx = std::tuple<Ctxs...>; | |
| 498 | using impl = conversion_category_impl<Ctx, T, Dir>; | |
| 499 | using index = typename impl::index; | |
| 500 | using next_supported = supported_context< | |
| 501 | mp11::mp_at< typename impl::ctxs, index >, T, Dir >; | |
| 502 | using type = typename next_supported::type; | |
| 503 | ||
| 504 | static | |
| 505 | type const& | |
| 506 | 19 | get( Ctx const& ctx ) noexcept |
| 507 | { | |
| 508 | 19 | return next_supported::get( std::get<index::value>( ctx ) ); |
| 509 | } | |
| 510 | }; | |
| 511 | ||
| 512 | template< class T > | |
| 513 | using value_result_type = typename std::decay< | |
| 514 | decltype( std::declval<T&>().value() )>::type; | |
| 515 | ||
| 516 | template< class T > | |
| 517 | using can_reset = decltype( std::declval<T&>().reset() ); | |
| 518 | ||
| 519 | template< class T > | |
| 520 | using has_valueless_by_exception = | |
| 521 | decltype( std::declval<T const&>().valueless_by_exception() ); | |
| 522 | ||
| 523 | } // namespace detail | |
| 524 | ||
| 525 | template <class T> | |
| 526 | struct result_for<T, value> | |
| 527 | { | |
| 528 | using type = system::result< detail::remove_cvref<T> >; | |
| 529 | }; | |
| 530 | ||
| 531 | template<class T> | |
| 532 | struct is_string_like | |
| 533 | : std::is_convertible<T, string_view> | |
| 534 | { }; | |
| 535 | ||
| 536 | template<class T> | |
| 537 | struct is_path_like | |
| 538 | : mp11::mp_all< | |
| 539 | mp11::mp_valid_and_true<detail::is_its_own_value, T>, | |
| 540 | mp11::mp_valid_and_true<detail::has_string_type, T>> | |
| 541 | { }; | |
| 542 | template<class T> | |
| 543 | struct is_sequence_like | |
| 544 | : mp11::mp_all< | |
| 545 | mp11::mp_valid_and_true<detail::are_begin_and_end_same, T>, | |
| 546 | mp11::mp_valid_and_true<detail::not_its_own_value, T>, | |
| 547 | mp11::mp_valid<detail::begin_iterator_category, T>> | |
| 548 | { }; | |
| 549 | ||
| 550 | template<class T> | |
| 551 | struct is_map_like | |
| 552 | : mp11::mp_all< | |
| 553 | is_sequence_like<T>, | |
| 554 | mp11::mp_valid_and_true<detail::is_value_type_pair, T>, | |
| 555 | is_string_like<detail::key_type<T>>, | |
| 556 | mp11::mp_valid_and_true<detail::has_unique_keys, T>> | |
| 557 | { }; | |
| 558 | ||
| 559 | template<class T> | |
| 560 | struct is_tuple_like | |
| 561 | : mp11::mp_valid_and_true<detail::has_positive_tuple_size, T> | |
| 562 | { }; | |
| 563 | ||
| 564 | template<> | |
| 565 | struct is_null_like<std::nullptr_t> | |
| 566 | : std::true_type | |
| 567 | { }; | |
| 568 | ||
| 569 | #ifndef BOOST_NO_CXX17_HDR_VARIANT | |
| 570 | template<> | |
| 571 | struct is_null_like<std::monostate> | |
| 572 | : std::true_type | |
| 573 | { }; | |
| 574 | #endif // BOOST_NO_CXX17_HDR_VARIANT | |
| 575 | ||
| 576 | template<class T> | |
| 577 | struct is_described_class | |
| 578 | : mp11::mp_and< | |
| 579 | describe::has_describe_members<T>, | |
| 580 | mp11::mp_not< std::is_union<T> >, | |
| 581 | mp11::mp_empty< | |
| 582 | mp11::mp_eval_or< | |
| 583 | mp11::mp_list<>, detail::described_non_public_members, T>>> | |
| 584 | { }; | |
| 585 | ||
| 586 | template<class T> | |
| 587 | struct is_described_enum | |
| 588 | : describe::has_describe_enumerators<T> | |
| 589 | { }; | |
| 590 | ||
| 591 | template<class T> | |
| 592 | struct is_variant_like : mp11::mp_valid<detail::has_valueless_by_exception, T> | |
| 593 | { }; | |
| 594 | ||
| 595 | template<class T> | |
| 596 | struct is_optional_like | |
| 597 | : mp11::mp_and< | |
| 598 | mp11::mp_not<std::is_void< | |
| 599 | mp11::mp_eval_or<void, detail::value_result_type, T>>>, | |
| 600 | mp11::mp_valid<detail::can_reset, T>> | |
| 601 | { }; | |
| 602 | ||
| 603 | } // namespace json | |
| 604 | } // namespace boost | |
| 605 | ||
| 606 | #endif // BOOST_JSON_IMPL_CONVERSION_HPP | |
| 607 |