value_from.hpp

92.3% Lines (12/13) 98.6% Functions (426/432) 100.0% Branches (4/4)

Covered Uncovered

value_from.hpp

12 covered 1 uncovered

Line	Branch	Hits	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		6970	value_from(
88			T&& t,
89			Context const& ctx,
90			value& jv)
91			{
92			using bare_T = detail::remove_cvref<T>;
93			BOOST_CORE_STATIC_ASSERT((
94			detail::conversion_round_trips<
95			Context, bare_T, detail::value_from_conversion>::value));
96			using cat = detail::value_from_category<Context, bare_T>;
97	1/1 ✓ Branch 2 taken 24 times.	6970	detail::value_from_impl( cat(), jv, std::forward<T>(t), ctx );
98		6970	}
99
100			/** Overload
101			@param t
102			@param ctx
103			@param sp A storage pointer referring to the memory resource to use for the
104			returned @ref value.
105
106			@return Overloads **(2)** and **(4)** return `t` converted to @ref value.
107			Overloads **(1)** and **3** return `void` instead and pass their result via
108			the out parameter `jv`.
109			*/
110			template< class T, class Context >
111			#ifndef BOOST_JSON_DOCS
112			typename std::enable_if<
113			!std::is_same< detail::remove_cvref<Context>, storage_ptr >::value &&
114			!std::is_same< detail::remove_cvref<Context>, value >::value,
115			value >::type
116			#else
117			value
118			#endif
119		6951	value_from(
120			T&& t,
121			Context const& ctx,
122			storage_ptr sp = {})
123			{
124		6951	value jv(std::move(sp));
125	1/1 ✓ Branch 1 taken 6951 times.	6951	value_from( static_cast<T&&>(t), ctx, jv );
126		6951	return jv;
127		✗	}
128
129			/// Overload
130			template<class T>
131			void
132		19	value_from(
133			T&& t,
134			value& jv)
135			{
136	1/1 ✓ Branch 1 taken 19 times.	19	value_from( static_cast<T&&>(t), detail::no_context(), jv );
137		19	}
138
139			/// Overload
140			template<class T>
141			value
142		222	value_from(
143			T&& t,
144			storage_ptr sp = {})
145			{
146			return value_from(
147	1/1 ✓ Branch 3 taken 1 time.	222	static_cast<T&&>(t), detail::no_context(), std::move(sp) );
148			}
149			/// @}
150
151			/** Determine if `T` can be converted to @ref value.
152
153			If `T` can be converted to @ref value via a call to @ref value_from, the
154			static data member `value` is defined as `true`. Otherwise, `value` is
155			defined as `false`.
156
157			@see @ref value_from.
158			*/
159			#ifdef BOOST_JSON_DOCS
160			template<class T>
161			using has_value_from = __see_below__;
162			#else
163			template<class T>
164			using has_value_from = detail::can_convert<
165			detail::remove_cvref<T>, detail::value_from_conversion>;
166			#endif
167
168			} // namespace json
169			} // namespace boost
170
171			#endif
172