| Line | Branch | Exec | Source |
|---|---|---|---|
| 1 | // | ||
| 2 | // Copyright (c) 2019 Vinnie Falco (vinnie.falco@gmail.com) | ||
| 3 | // Copyright (c) 2020 Krystian Stasiowski (sdkrystian@gmail.com) | ||
| 4 | // Copyright (c) 2022 Dmitry Arkhipov (grisumbras@gmail.com) | ||
| 5 | // | ||
| 6 | // Distributed under the Boost Software License, Version 1.0. (See accompanying | ||
| 7 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | ||
| 8 | // | ||
| 9 | // Official repository: https://github.com/boostorg/json | ||
| 10 | // | ||
| 11 | |||
| 12 | #ifndef BOOST_JSON_VALUE_TO_HPP | ||
| 13 | #define BOOST_JSON_VALUE_TO_HPP | ||
| 14 | |||
| 15 | #include <boost/json/detail/value_to.hpp> | ||
| 16 | |||
| 17 | namespace boost { | ||
| 18 | namespace json { | ||
| 19 | |||
| 20 | /** Convert a @ref value to an object of type `T`. | ||
| 21 | |||
| 22 | This function attempts to convert a @ref value | ||
| 23 | to `T` using | ||
| 24 | |||
| 25 | @li one of @ref value's accessors, or | ||
| 26 | @li a library-provided generic conversion, or | ||
| 27 | @li a user-provided overload of `tag_invoke`. | ||
| 28 | |||
| 29 | Out of the box the function supports default constructible types satisfying | ||
| 30 | {req_SequenceContainer}, arrays, arithmetic types, `bool`, `std::tuple`, | ||
| 31 | `std::pair`, `std::optional`, `std::variant`, `std::nullptr_t`, and structs | ||
| 32 | and enums described using Boost.Describe. | ||
| 33 | |||
| 34 | Conversion of other types is done by calling an overload of `tag_invoke` | ||
| 35 | found by argument-dependent lookup. Its signature should be similar to: | ||
| 36 | |||
| 37 | @code | ||
| 38 | template< class FullContext > | ||
| 39 | T tag_invoke( value_to_tag<T>, const value&, const Context& , const FullContext& ); | ||
| 40 | @endcode | ||
| 41 | |||
| 42 | or | ||
| 43 | |||
| 44 | @code | ||
| 45 | T tag_invoke( value_to_tag<T>, const value&, const Context& ); | ||
| 46 | @endcode | ||
| 47 | |||
| 48 | or | ||
| 49 | |||
| 50 | @code | ||
| 51 | result<T> tag_invoke( value_to_tag<T>, const value& ); | ||
| 52 | @endcode | ||
| 53 | |||
| 54 | The overloads are checked for existence in that order and the first that | ||
| 55 | matches will be selected. | ||
| 56 | |||
| 57 | The object returned by the function call is returned by @ref value_to as | ||
| 58 | the result of the conversion. | ||
| 59 | |||
| 60 | The `ctx` argument can be used either as a tag type to provide conversions | ||
| 61 | for third-party types, or to pass extra data to the conversion function. | ||
| 62 | |||
| 63 | Overload **(3)** is **deleted** and participates in overload resolution | ||
| 64 | only when `U` is not @ref value. The overload exists to prevent unintented | ||
| 65 | creation of temporary @ref value instances, e.g. | ||
| 66 | |||
| 67 | @code | ||
| 68 | auto flag = value_to<bool>(true); | ||
| 69 | @endcode | ||
| 70 | |||
| 71 | @par Constraints | ||
| 72 | @code | ||
| 73 | ! std::is_reference< T >::value | ||
| 74 | @endcode | ||
| 75 | |||
| 76 | @par Exception Safety | ||
| 77 | Strong guarantee. | ||
| 78 | |||
| 79 | @tparam T The type to convert to. | ||
| 80 | |||
| 81 | @tparam Context The type of context passed to the conversion function. | ||
| 82 | |||
| 83 | @returns `jv` converted to `result<T>`. | ||
| 84 | |||
| 85 | @param jv The @ref value to convert. | ||
| 86 | |||
| 87 | @param ctx Context passed to the conversion function. | ||
| 88 | |||
| 89 | @see @ref value_to_tag, @ref value_from, | ||
| 90 | <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf"> | ||
| 91 | tag_invoke: A general pattern for supporting customisable functions</a> | ||
| 92 | |||
| 93 | @{ | ||
| 94 | */ | ||
| 95 | template< class T, class Context > | ||
| 96 | T | ||
| 97 | 808 | value_to( value const& jv, Context const& ctx ) | |
| 98 | { | ||
| 99 | BOOST_STATIC_ASSERT(! std::is_reference<T>::value); | ||
| 100 | using bare_T = detail::remove_cvref<T>; | ||
| 101 | BOOST_STATIC_ASSERT(detail::conversion_round_trips< | ||
| 102 | Context, bare_T, detail::value_to_conversion>::value); | ||
| 103 | using cat = detail::value_to_category<Context, bare_T>; | ||
| 104 | 808 | return detail::value_to_impl( cat(), value_to_tag<bare_T>(), jv, ctx ); | |
| 105 | } | ||
| 106 | |||
| 107 | /// Overload | ||
| 108 | template<class T> | ||
| 109 | T | ||
| 110 | 249 | value_to(const value& jv) | |
| 111 | { | ||
| 112 |
1/1✓ Branch 1 taken 103 times.
|
371 | return value_to<T>( jv, detail::no_context() ); |
| 113 | } | ||
| 114 | |||
| 115 | /// Overload | ||
| 116 | template<class T, class U | ||
| 117 | #ifndef BOOST_JSON_DOCS | ||
| 118 | , class = typename std::enable_if<!std::is_same<U, value>::value>::type | ||
| 119 | #endif | ||
| 120 | > | ||
| 121 | T | ||
| 122 | value_to(U const& jv) = delete; | ||
| 123 | /// @} | ||
| 124 | |||
| 125 | /** Convert a @ref value to a @ref boost::system::result. | ||
| 126 | |||
| 127 | This function attempts to convert a @ref value to `result<T>` using | ||
| 128 | |||
| 129 | @li one of @ref value's accessors, or | ||
| 130 | @li a library-provided generic conversion, or | ||
| 131 | @li a user-provided overload of `tag_invoke`. | ||
| 132 | |||
| 133 | Out of the box the function supports default constructible types satisfying | ||
| 134 | {req_SequenceContainer}, arrays, arithmetic types, `bool`, `std::tuple`, | ||
| 135 | `std::pair`, `std::optional`, `std::variant`, `std::nullptr_t`, and structs | ||
| 136 | and enums described using Boost.Describe. | ||
| 137 | |||
| 138 | Conversion of other types is done by calling an overload of `tag_invoke` | ||
| 139 | found by argument-dependent lookup. Its signature should be similar to: | ||
| 140 | |||
| 141 | @code | ||
| 142 | template< class FullContext > | ||
| 143 | result<T> tag_invoke( try_value_to_tag<T>, const value&, const Context& , const FullContext& ); | ||
| 144 | @endcode | ||
| 145 | |||
| 146 | or | ||
| 147 | |||
| 148 | @code | ||
| 149 | result<T> tag_invoke( try_value_to_tag<T>, const value&, const Context& ); | ||
| 150 | @endcode | ||
| 151 | |||
| 152 | or | ||
| 153 | |||
| 154 | @code | ||
| 155 | result<T> tag_invoke( try_value_to_tag<T>, const value& ); | ||
| 156 | @endcode | ||
| 157 | |||
| 158 | The overloads are checked for existence in that order and the first that | ||
| 159 | matches will be selected. | ||
| 160 | |||
| 161 | If an error occurs during conversion, the result will store the error code | ||
| 162 | associated with the error. If an exception is thrown, the function will | ||
| 163 | attempt to retrieve the associated error code and return it, otherwise it | ||
| 164 | will return `error::exception`, unless the exception type is | ||
| 165 | @ref std::bad_alloc, which will be allowed to propagate. | ||
| 166 | |||
| 167 | The `ctx` argument can be used either as a tag type to provide conversions | ||
| 168 | for third-party types, or to pass extra data to the conversion function. | ||
| 169 | |||
| 170 | @par Constraints | ||
| 171 | @code | ||
| 172 | ! std::is_reference< T >::value | ||
| 173 | @endcode | ||
| 174 | |||
| 175 | @par Exception Safety | ||
| 176 | Strong guarantee. | ||
| 177 | |||
| 178 | @tparam T The type to convert to. | ||
| 179 | @tparam Context The type of context passed to the conversion function. | ||
| 180 | |||
| 181 | @param jv The @ref value to convert. | ||
| 182 | @param ctx Context passed to the conversion function. | ||
| 183 | |||
| 184 | @returns `jv` converted to `result<T>`. | ||
| 185 | |||
| 186 | @see @ref value_to_tag, @ref value_to, @ref value_from, | ||
| 187 | [tag_invoke: A general pattern for supporting customisable functions](http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf). | ||
| 188 | |||
| 189 | @{ | ||
| 190 | */ | ||
| 191 | template< class T, class Context > | ||
| 192 | typename result_for<T, value>::type | ||
| 193 | 7486 | try_value_to( value const& jv, Context const& ctx ) | |
| 194 | { | ||
| 195 | BOOST_STATIC_ASSERT(! std::is_reference<T>::value); | ||
| 196 | using bare_T = detail::remove_cvref<T>; | ||
| 197 | BOOST_STATIC_ASSERT(detail::conversion_round_trips< | ||
| 198 | Context, bare_T, detail::value_to_conversion>::value); | ||
| 199 | using cat = detail::value_to_category<Context, bare_T>; | ||
| 200 | 7106 | return detail::value_to_impl( | |
| 201 | 7474 | cat(), try_value_to_tag<bare_T>(), jv, ctx ); | |
| 202 | } | ||
| 203 | |||
| 204 | /// Overload | ||
| 205 | template<class T> | ||
| 206 | typename result_for<T, value>::type | ||
| 207 | 130 | try_value_to(const value& jv) | |
| 208 | { | ||
| 209 |
1/1✓ Branch 1 taken 4 times.
|
163 | return try_value_to<T>( jv, detail::no_context() ); |
| 210 | } | ||
| 211 | /// @} | ||
| 212 | |||
| 213 | /** Determine if a @ref value can be converted to `T`. | ||
| 214 | |||
| 215 | If @ref value can be converted to `T` via a | ||
| 216 | call to @ref value_to, the static data member `value` | ||
| 217 | is defined as `true`. Otherwise, `value` is | ||
| 218 | defined as `false`. | ||
| 219 | |||
| 220 | @see @ref value_to | ||
| 221 | */ | ||
| 222 | #ifdef BOOST_JSON_DOCS | ||
| 223 | template<class T> | ||
| 224 | using has_value_to = __see_below__; | ||
| 225 | #else | ||
| 226 | template<class T> | ||
| 227 | using has_value_to = detail::can_convert< | ||
| 228 | detail::remove_cvref<T>, detail::value_to_conversion>; | ||
| 229 | #endif | ||
| 230 | |||
| 231 | } // namespace json | ||
| 232 | } // namespace boost | ||
| 233 | |||
| 234 | #endif | ||
| 235 |