1/*
2 * Copyright Andrey Semashev 2007 - 2015.
3 * Distributed under the Boost Software License, Version 1.0.
4 * (See accompanying file LICENSE_1_0.txt or copy at
5 * http://www.boost.org/LICENSE_1_0.txt)
6 */
7/*!
8 * \file fallback_policy.hpp
9 * \author Andrey Semashev
10 * \date 18.08.2012
11 *
12 * The header contains definition of fallback policies when attribute value visitation or extraction fails.
13 */
14
15#ifndef BOOST_LOG_ATTRIBUTES_FALLBACK_POLICY_HPP_INCLUDED_
16#define BOOST_LOG_ATTRIBUTES_FALLBACK_POLICY_HPP_INCLUDED_
17
18#include <boost/type_index.hpp>
19#include <boost/type_traits/remove_cv.hpp>
20#include <boost/type_traits/remove_reference.hpp>
21#include <boost/log/detail/config.hpp>
22#include <boost/log/exceptions.hpp>
23#include <boost/log/attributes/fallback_policy_fwd.hpp>
24#include <boost/log/detail/header.hpp>
25
26#ifdef BOOST_HAS_PRAGMA_ONCE
27#pragma once
28#endif
29
30namespace boost {
31
32BOOST_LOG_OPEN_NAMESPACE
33
34/*!
35 * The \c fallback_to_none policy results in returning an empty value reference if the attribute value cannot be extracted.
36 */
37struct fallback_to_none
38{
39 enum { guaranteed_result = false };
40
41 /*!
42 * The method is called in order to apply a function object to the default value.
43 */
44 template< typename FunT >
45 static bool apply_default(FunT&)
46 {
47 return false;
48 }
49
50 /*!
51 * The method is called in order to apply a function object to the default value.
52 */
53 template< typename FunT >
54 static bool apply_default(FunT const&)
55 {
56 return false;
57 }
58
59 /*!
60 * The method is called when value extraction failed because the attribute value has different type than requested.
61 */
62 static void on_invalid_type(typeindex::type_index const&)
63 {
64 }
65
66 /*!
67 * The method is called when value extraction failed because the attribute value was not found.
68 */
69 static void on_missing_value()
70 {
71 }
72};
73
74/*!
75 * The \c fallback_to_throw policy results in throwing an exception if the attribute value cannot be extracted.
76 */
77struct fallback_to_throw
78{
79 enum { guaranteed_result = true };
80
81 /*!
82 * The method is called in order to apply a function object to the default value.
83 */
84 template< typename FunT >
85 static bool apply_default(FunT&)
86 {
87 return false;
88 }
89
90 /*!
91 * The method is called in order to apply a function object to the default value.
92 */
93 template< typename FunT >
94 static bool apply_default(FunT const&)
95 {
96 return false;
97 }
98
99 /*!
100 * The method is called when value extraction failed because the attribute value has different type than requested.
101 */
102 static void on_invalid_type(typeindex::type_index const& t)
103 {
104 BOOST_LOG_THROW_DESCR_PARAMS(invalid_type, "Attribute value has incompatible type", (t));
105 }
106
107 /*!
108 * The method is called when value extraction failed because the attribute value was not found.
109 */
110 static void on_missing_value()
111 {
112 BOOST_LOG_THROW_DESCR(missing_value, "Attribute value not found");
113 }
114};
115
116/*!
117 * The \c fallback_to_default policy results in a default value if the attribute value cannot be extracted.
118 */
119template< typename DefaultT >
120struct fallback_to_default
121{
122 enum { guaranteed_result = true };
123
124 //! Default value type
125 typedef typename remove_cv< typename remove_reference< DefaultT >::type >::type default_type;
126
127 /*!
128 * Default constructor.
129 */
130 fallback_to_default() : m_default()
131 {
132 }
133
134 /*!
135 * Initializing constructor.
136 */
137 explicit fallback_to_default(default_type const& def_val) : m_default(def_val)
138 {
139 }
140
141 /*!
142 * The method is called in order to apply a function object to the default value.
143 */
144 template< typename FunT >
145 bool apply_default(FunT& fun) const
146 {
147 fun(m_default);
148 return true;
149 }
150
151 /*!
152 * The method is called in order to apply a function object to the default value.
153 */
154 template< typename FunT >
155 bool apply_default(FunT const& fun) const
156 {
157 fun(m_default);
158 return true;
159 }
160
161 /*!
162 * The method is called when value extraction failed because the attribute value has different type than requested.
163 */
164 static void on_invalid_type(typeindex::type_index const&)
165 {
166 }
167
168 /*!
169 * The method is called when value extraction failed because the attribute value was not found.
170 */
171 static void on_missing_value()
172 {
173 }
174
175private:
176 //! Default value
177 DefaultT m_default;
178};
179
180BOOST_LOG_CLOSE_NAMESPACE // namespace log
181
182} // namespace boost
183
184#include <boost/log/detail/footer.hpp>
185
186#endif // BOOST_LOG_ATTRIBUTES_FALLBACK_POLICY_HPP_INCLUDED_
187

source code of boost/libs/log/include/boost/log/attributes/fallback_policy.hpp