TLA Line data Source code
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_FROM_HPP
13 : #define BOOST_JSON_VALUE_FROM_HPP
14 :
15 : #include <boost/core/detail/static_assert.hpp>
16 : #include <boost/json/detail/value_from.hpp>
17 :
18 : namespace boost {
19 : namespace json {
20 :
21 : /** Convert an object of type `T` to @ref value.
22 :
23 : This function attempts to convert an object
24 : of type `T` to @ref value using
25 :
26 : @li one of @ref value's constructors,
27 :
28 : @li a library-provided generic conversion, or
29 :
30 : @li a user-provided overload of `tag_invoke`.
31 :
32 : Out of the function supports default constructible types satisfying
33 : {req_SequenceContainer}, arrays, arithmetic types, `bool`, `std::tuple`,
34 : `std::pair`, `std::optional`, `std::variant`, `std::nullptr_t`, and structs
35 : and enums described using Boost.Describe.
36 :
37 : Conversion of other types is done by calling an overload of `tag_invoke`
38 : found by argument-dependent lookup. Its signature should be similar to:
39 :
40 : @code
41 : template< class FullContext >
42 : void tag_invoke( value_from_tag, value&, T, const Context&, const FullContext& );
43 : @endcode
44 :
45 : or
46 :
47 : @code
48 : void tag_invoke( value_from_tag, value&, T, const Context& );
49 : @endcode
50 :
51 : or
52 :
53 : @code
54 : void tag_invoke( value_from_tag, value&, T );
55 : @endcode
56 :
57 : The overloads are checked for existence in that order and the first that
58 : matches will be selected. <br>
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 : Overloads **(2)** and **(4)** construct their return value using the
64 : @ref storage_ptr `sp`, which ensures that the memory resource is correctly
65 : propagated.
66 :
67 : @par Exception Safety
68 : Strong guarantee.
69 :
70 : @tparam T The type of the object to convert.
71 :
72 : @tparam Context The type of context passed to the conversion function.
73 :
74 : @param t The object to convert.
75 :
76 : @param ctx Context passed to the conversion function.
77 :
78 : @param jv @ref value out parameter.
79 :
80 : @see @ref value_from_tag, @ref value_to,
81 : <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1895r0.pdf">
82 : tag_invoke: A general pattern for supporting customisable functions</a>
83 : */
84 : /// @{
85 : template< class T, class Context >
86 : void
87 HIT 7056 : value_from(
88 : T&& t,
89 : Context const& ctx,
90 : value& jv)
91 : {
92 : using bare_T = detail::remove_cvref<T>;
93 : using cat = detail::value_from_category<Context, bare_T>;
94 7056 : detail::value_from_impl( cat(), jv, std::forward<T>(t), ctx );
95 7056 : }
96 :
97 : /** Overload
98 : @param t
99 : @param ctx
100 : @param sp A storage pointer referring to the memory resource to use for the
101 : returned @ref value.
102 :
103 : @return Overloads **(2)** and **(4)** return `t` converted to @ref value.
104 : Overloads **(1)** and **3** return `void` instead and pass their result via
105 : the out parameter `jv`.
106 : */
107 : template< class T, class Context >
108 : #ifndef BOOST_JSON_DOCS
109 : typename std::enable_if<
110 : !std::is_same< detail::remove_cvref<Context>, storage_ptr >::value &&
111 : !std::is_same< detail::remove_cvref<Context>, value >::value,
112 : value >::type
113 : #else
114 : value
115 : #endif
116 7037 : value_from(
117 : T&& t,
118 : Context const& ctx,
119 : storage_ptr sp = {})
120 : {
121 7037 : value jv(std::move(sp));
122 7037 : value_from( static_cast<T&&>(t), ctx, jv );
123 7037 : return jv;
124 MIS 0 : }
125 :
126 : /// Overload
127 : template<class T>
128 : void
129 HIT 19 : value_from(
130 : T&& t,
131 : value& jv)
132 : {
133 19 : value_from( static_cast<T&&>(t), detail::no_context(), jv );
134 19 : }
135 :
136 : /// Overload
137 : template<class T>
138 : value
139 297 : value_from(
140 : T&& t,
141 : storage_ptr sp = {})
142 : {
143 : return value_from(
144 297 : static_cast<T&&>(t), detail::no_context(), std::move(sp) );
145 : }
146 : /// @}
147 :
148 : /** Determine if `T` can be converted to @ref value.
149 :
150 : If `T` can be converted to @ref value via a call to @ref value_from, the
151 : static data member `value` is defined as `true`. Otherwise, `value` is
152 : defined as `false`.
153 :
154 : @see @ref value_from.
155 : */
156 : #ifdef BOOST_JSON_DOCS
157 : template<class T>
158 : using has_value_from = __see_below__;
159 : #else
160 : template<class T>
161 : using has_value_from = detail::can_convert<
162 : detail::remove_cvref<T>, detail::value_from_conversion>;
163 : #endif
164 :
165 : } // namespace json
166 : } // namespace boost
167 :
168 : #endif
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