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 value_visitation.hpp
9 * \author Andrey Semashev
10 * \date 01.03.2008
11 *
12 * The header contains implementation of convenience tools to apply visitors to an attribute value
13 * in the view.
14 */
15
16#ifndef BOOST_LOG_ATTRIBUTES_VALUE_VISITATION_HPP_INCLUDED_
17#define BOOST_LOG_ATTRIBUTES_VALUE_VISITATION_HPP_INCLUDED_
18
19#include <boost/core/explicit_operator_bool.hpp>
20#include <boost/log/detail/config.hpp>
21#include <boost/log/exceptions.hpp>
22#include <boost/log/core/record.hpp>
23#include <boost/log/attributes/attribute_name.hpp>
24#include <boost/log/attributes/attribute_value.hpp>
25#include <boost/log/attributes/attribute.hpp>
26#include <boost/log/attributes/attribute_value_set.hpp>
27#include <boost/log/attributes/value_visitation_fwd.hpp>
28#include <boost/log/attributes/fallback_policy.hpp>
29#include <boost/log/expressions/keyword_fwd.hpp>
30#include <boost/log/utility/type_dispatch/static_type_dispatcher.hpp>
31#include <boost/log/detail/header.hpp>
32
33#ifdef BOOST_HAS_PRAGMA_ONCE
34#pragma once
35#endif
36
37namespace boost {
38
39BOOST_LOG_OPEN_NAMESPACE
40
41/*!
42 * \brief The class represents attribute value visitation result
43 *
44 * The main purpose of this class is to provide a convenient interface for checking
45 * whether the attribute value visitation succeeded or not. It also allows to discover
46 * the actual cause of failure, should the operation fail.
47 */
48class visitation_result
49{
50public:
51 //! Error codes for attribute value visitation
52 enum error_code
53 {
54 ok, //!< The attribute value has been visited successfully
55 value_not_found, //!< The attribute value is not present in the view
56 value_has_invalid_type //!< The attribute value is present in the view, but has an unexpected type
57 };
58
59private:
60 error_code m_code;
61
62public:
63 /*!
64 * Initializing constructor. Creates the result that is equivalent to the
65 * specified error code.
66 */
67 BOOST_CONSTEXPR visitation_result(error_code code = ok) BOOST_NOEXCEPT : m_code(code) {}
68
69 /*!
70 * Checks if the visitation was successful.
71 *
72 * \return \c true if the value was visited successfully, \c false otherwise.
73 */
74 BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT()
75 /*!
76 * Checks if the visitation was unsuccessful.
77 *
78 * \return \c false if the value was visited successfully, \c true otherwise.
79 */
80 bool operator! () const BOOST_NOEXCEPT { return (m_code != ok); }
81
82 /*!
83 * \return The actual result code of value visitation
84 */
85 error_code code() const BOOST_NOEXCEPT { return m_code; }
86};
87
88/*!
89 * \brief Generic attribute value visitor invoker
90 *
91 * Attribute value invoker is a functional object that attempts to find and extract the stored
92 * attribute value from the attribute value view or a log record. The extracted value is passed to
93 * a unary function object (the visitor) provided by user.
94 *
95 * The invoker can be specialized on one or several attribute value types that should be
96 * specified in the second template argument.
97 */
98template< typename T, typename FallbackPolicyT >
99class value_visitor_invoker :
100 private FallbackPolicyT
101{
102 typedef value_visitor_invoker< T, FallbackPolicyT > this_type;
103
104public:
105 //! Attribute value types
106 typedef T value_type;
107
108 //! Fallback policy
109 typedef FallbackPolicyT fallback_policy;
110
111 //! Function object result type
112 typedef visitation_result result_type;
113
114public:
115 /*!
116 * Default constructor
117 */
118 BOOST_DEFAULTED_FUNCTION(value_visitor_invoker(), {})
119
120 /*!
121 * Copy constructor
122 */
123 value_visitor_invoker(value_visitor_invoker const& that) : fallback_policy(static_cast< fallback_policy const& >(that))
124 {
125 }
126
127 /*!
128 * Initializing constructor
129 *
130 * \param arg Fallback policy argument
131 */
132 template< typename U >
133 explicit value_visitor_invoker(U const& arg) : fallback_policy(arg) {}
134
135 /*!
136 * Visitation operator. Attempts to acquire the stored value of one of the supported types. If acquisition succeeds,
137 * the value is passed to \a visitor.
138 *
139 * \param attr An attribute value to apply the visitor to.
140 * \param visitor A receiving function object to pass the attribute value to.
141 * \return The result of visitation.
142 */
143 template< typename VisitorT >
144 result_type operator() (attribute_value const& attr, VisitorT visitor) const
145 {
146 if (!!attr)
147 {
148 static_type_dispatcher< value_type > disp(visitor);
149 if (attr.dispatch(dispatcher&: disp) || fallback_policy::apply_default(visitor))
150 {
151 return visitation_result::ok;
152 }
153 else
154 {
155 fallback_policy::on_invalid_type(attr.get_type());
156 return visitation_result::value_has_invalid_type;
157 }
158 }
159
160 if (fallback_policy::apply_default(visitor))
161 return visitation_result::ok;
162
163 fallback_policy::on_missing_value();
164 return visitation_result::value_not_found;
165 }
166
167 /*!
168 * Visitation operator. Looks for an attribute value with the specified name
169 * and tries to acquire the stored value of one of the supported types. If acquisition succeeds,
170 * the value is passed to \a visitor.
171 *
172 * \param name Attribute value name.
173 * \param attrs A set of attribute values in which to look for the specified attribute value.
174 * \param visitor A receiving function object to pass the attribute value to.
175 * \return The result of visitation.
176 */
177 template< typename VisitorT >
178 result_type operator() (attribute_name const& name, attribute_value_set const& attrs, VisitorT visitor) const
179 {
180 try
181 {
182 attribute_value_set::const_iterator it = attrs.find(key: name);
183 if (it != attrs.end())
184 return operator() (it->second, visitor);
185 else
186 return operator() (attribute_value(), visitor);
187 }
188 catch (exception& e)
189 {
190 // Attach the attribute name to the exception
191 boost::log::aux::attach_attribute_name_info(e, name);
192 throw;
193 }
194 }
195
196 /*!
197 * Visitation operator. Looks for an attribute value with the specified name
198 * and tries to acquire the stored value of one of the supported types. If acquisition succeeds,
199 * the value is passed to \a visitor.
200 *
201 * \param name Attribute value name.
202 * \param rec A log record. The attribute value will be sought among those associated with the record.
203 * \param visitor A receiving function object to pass the attribute value to.
204 * \return The result of visitation.
205 */
206 template< typename VisitorT >
207 result_type operator() (attribute_name const& name, record const& rec, VisitorT visitor) const
208 {
209 return operator() (name, rec.attribute_values(), visitor);
210 }
211
212 /*!
213 * Visitation operator. Looks for an attribute value with the specified name
214 * and tries to acquire the stored value of one of the supported types. If acquisition succeeds,
215 * the value is passed to \a visitor.
216 *
217 * \param name Attribute value name.
218 * \param rec A log record view. The attribute value will be sought among those associated with the record.
219 * \param visitor A receiving function object to pass the attribute value to.
220 * \return The result of visitation.
221 */
222 template< typename VisitorT >
223 result_type operator() (attribute_name const& name, record_view const& rec, VisitorT visitor) const
224 {
225 return operator() (name, rec.attribute_values(), visitor);
226 }
227
228 /*!
229 * \returns Fallback policy
230 */
231 fallback_policy const& get_fallback_policy() const
232 {
233 return *static_cast< fallback_policy const* >(this);
234 }
235};
236
237/*!
238 * The function applies a visitor to an attribute value from the view. The user has to explicitly specify the
239 * type or set of possible types of the attribute value to be visited.
240 *
241 * \param name The name of the attribute value to visit.
242 * \param attrs A set of attribute values in which to look for the specified attribute value.
243 * \param visitor A receiving function object to pass the attribute value to.
244 * \return The result of visitation.
245 */
246template< typename T, typename VisitorT >
247inline visitation_result
248visit(attribute_name const& name, attribute_value_set const& attrs, VisitorT visitor)
249{
250 value_visitor_invoker< T > invoker;
251 return invoker(name, attrs, visitor);
252}
253
254/*!
255 * The function applies a visitor to an attribute value from the view. The user has to explicitly specify the
256 * type or set of possible types of the attribute value to be visited.
257 *
258 * \param name The name of the attribute value to visit.
259 * \param rec A log record. The attribute value will be sought among those associated with the record.
260 * \param visitor A receiving function object to pass the attribute value to.
261 * \return The result of visitation.
262 */
263template< typename T, typename VisitorT >
264inline visitation_result
265visit(attribute_name const& name, record const& rec, VisitorT visitor)
266{
267 value_visitor_invoker< T > invoker;
268 return invoker(name, rec, visitor);
269}
270
271/*!
272 * The function applies a visitor to an attribute value from the view. The user has to explicitly specify the
273 * type or set of possible types of the attribute value to be visited.
274 *
275 * \param name The name of the attribute value to visit.
276 * \param rec A log record view. The attribute value will be sought among those associated with the record.
277 * \param visitor A receiving function object to pass the attribute value to.
278 * \return The result of visitation.
279 */
280template< typename T, typename VisitorT >
281inline visitation_result
282visit(attribute_name const& name, record_view const& rec, VisitorT visitor)
283{
284 value_visitor_invoker< T > invoker;
285 return invoker(name, rec, visitor);
286}
287
288/*!
289 * The function applies a visitor to an attribute value. The user has to explicitly specify the
290 * type or set of possible types of the attribute value to be visited.
291 *
292 * \param value The attribute value to visit.
293 * \param visitor A receiving function object to pass the attribute value to.
294 * \return The result of visitation.
295 */
296template< typename T, typename VisitorT >
297inline visitation_result
298visit(attribute_value const& value, VisitorT visitor)
299{
300 value_visitor_invoker< T > invoker;
301 return invoker(value, visitor);
302}
303
304/*!
305 * The function applies a visitor to an attribute value from the view. The user has to explicitly specify the
306 * type or set of possible types of the attribute value to be visited.
307 *
308 * \param keyword The keyword of the attribute value to visit.
309 * \param attrs A set of attribute values in which to look for the specified attribute value.
310 * \param visitor A receiving function object to pass the attribute value to.
311 * \return The result of visitation.
312 */
313template< typename DescriptorT, template< typename > class ActorT, typename VisitorT >
314inline visitation_result
315visit(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, attribute_value_set const& attrs, VisitorT visitor)
316{
317 value_visitor_invoker< typename DescriptorT::value_type > invoker;
318 return invoker(keyword.get_name(), attrs, visitor);
319}
320
321/*!
322 * The function applies a visitor to an attribute value from the view. The user has to explicitly specify the
323 * type or set of possible types of the attribute value to be visited.
324 *
325 * \param keyword The keyword of the attribute value to visit.
326 * \param rec A log record. The attribute value will be sought among those associated with the record.
327 * \param visitor A receiving function object to pass the attribute value to.
328 * \return The result of visitation.
329 */
330template< typename DescriptorT, template< typename > class ActorT, typename VisitorT >
331inline visitation_result
332visit(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, record const& rec, VisitorT visitor)
333{
334 value_visitor_invoker< typename DescriptorT::value_type > invoker;
335 return invoker(keyword.get_name(), rec, visitor);
336}
337
338/*!
339 * The function applies a visitor to an attribute value from the view. The user has to explicitly specify the
340 * type or set of possible types of the attribute value to be visited.
341 *
342 * \param keyword The keyword of the attribute value to visit.
343 * \param rec A log record view. The attribute value will be sought among those associated with the record.
344 * \param visitor A receiving function object to pass the attribute value to.
345 * \return The result of visitation.
346 */
347template< typename DescriptorT, template< typename > class ActorT, typename VisitorT >
348inline visitation_result
349visit(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, record_view const& rec, VisitorT visitor)
350{
351 value_visitor_invoker< typename DescriptorT::value_type > invoker;
352 return invoker(keyword.get_name(), rec, visitor);
353}
354
355
356#if !defined(BOOST_LOG_DOXYGEN_PASS)
357
358template< typename T, typename VisitorT >
359inline visitation_result attribute_value::visit(VisitorT visitor) const
360{
361 return boost::log::visit< T >(*this, visitor);
362}
363
364#endif // !defined(BOOST_LOG_DOXYGEN_PASS)
365
366BOOST_LOG_CLOSE_NAMESPACE // namespace log
367
368} // namespace boost
369
370#include <boost/log/detail/footer.hpp>
371
372#endif // BOOST_LOG_ATTRIBUTES_VALUE_VISITATION_HPP_INCLUDED_
373

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