GCC Code Coverage Report

Line	Branch	Exec	Source
1			//
2			// Copyright (c) 2019 Vinnie Falco (vinnie.falco@gmail.com)
3			// Copyright (c) 2024 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_RESULT_FOR_HPP
12			#define BOOST_JSON_RESULT_FOR_HPP
13
14			#include <boost/json/detail/config.hpp>
15			#include <boost/json/fwd.hpp>
16			#include <boost/assert/source_location.hpp>
17			#include <boost/system/result.hpp>
18
19			namespace boost {
20			namespace json {
21
22			/**
23			Helper trait that returns @ref boost::system::result.
24
25			The primary template is an incomplete type. The library provides a partial
26			specialisation `result_for<T1, value>`, that has nested type alias `type`
27			that aliases the type `result<T1>`.
28
29			The purpose of this trait is to let users provide non-throwing conversions
30			for their types without creating a physical dependency on Boost.Json. For
31			example:
32
33			@code
34			namespace boost {
35			namespace json {
36
37			template<class T>
38			struct value_to_tag;
39
40			template<class T1, class T2>
41			struct result_for;
42			}
43			}
44
45			namespace mine
46			{
47			class my_class;
48			...
49			template<class JsonValue>
50			boost::json::result_for<my_class, JsonValue>
51			tag_invoke(boost::json::try_value_to_tag<my_class>, const JsonValue& jv)
52			{ ... }
53			}
54			@endcode
55
56			@see @ref try_value_to, @ref try_value_to_tag
57			*/
58			template <class T1, class T2>
59			struct result_for;
60
61			/** Create @ref boost::system::result containing a portable error code.
62
63			This function constructs a `boost::system::result<T>` that stores
64			`error_code` with `value()` equal to `e` and `category()` equal to
65			@ref boost::system::generic_category().
66
67			The main use for this function is in implementation of functions returning
68			`boost::system::result`, without including `boost/json/system_error.hpp` or
69			even `<system_error>`. In particular, it may be useful for customizations
70			of @ref try_value_to without creating a physical dependency on Boost.JSON.
71			For example:
72
73			@code
74			#include <cerrno>
75			#include <boost/assert/source_location.hpp>
76
77			namespace boost {
78			namespace json {
79
80			class value;
81
82			template<class T>
83			struct try_value_to_tag;
84
85			template<class T1, class T2>
86			struct result_for;
87
88			template <class T>
89			typename result_for<T, value>::type
90			result_from_errno(int e, boost::source_location const* loc) noexcept
91
92			}
93			}
94
95			namespace mine {
96
97			class my_class;
98			...
99			template<class JsonValue>
100			boost::json::result_for<my_class, JsonValue>
101			tag_invoke(boost::json::try_value_to_tag<my_class>, const JsonValue& jv)
102			{
103			BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION;
104			if( !jv.is_null() )
105			return boost::json::result_from_errno<my_class>(EINVAL, &loc);
106			return my_class();
107			}
108
109			}
110			@endcode
111
112			@par Exception Safety
113			Does not throw exceptions.
114
115			@tparam T The value type of returned `result`.
116			@param e The error value.
117			@param loc The error location.
118
119			@returns A @ref boost::system::result containing an error.
120
121			@see @ref try_value_to_tag, @ref try_value_to, @ref result_for.
122			*/
123			template <class T>
124			typename result_for<T, value>::type
125		56	result_from_errno(int e, boost::source_location const* loc) noexcept
126			{
127		56	system::error_code ec(e, system::generic_category(), loc);
128		56	return {system::in_place_error, ec};
129			}
130
131			} // namespace json
132			} // namespace boost
133
134			#endif // BOOST_JSON_RESULT_FOR_HPP
135