373 lines
14 KiB
C++
373 lines
14 KiB
C++
/*
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* Copyright Andrey Semashev 2007 - 2015.
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* Distributed under the Boost Software License, Version 1.0.
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* (See accompanying file LICENSE_1_0.txt or copy at
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* http://www.boost.org/LICENSE_1_0.txt)
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*/
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/*!
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* \file value_visitation.hpp
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* \author Andrey Semashev
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* \date 01.03.2008
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*
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* The header contains implementation of convenience tools to apply visitors to an attribute value
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* in the view.
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*/
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#ifndef BOOST_LOG_ATTRIBUTES_VALUE_VISITATION_HPP_INCLUDED_
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#define BOOST_LOG_ATTRIBUTES_VALUE_VISITATION_HPP_INCLUDED_
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#include <boost/log/detail/config.hpp>
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#include <boost/log/exceptions.hpp>
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#include <boost/log/core/record.hpp>
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#include <boost/log/attributes/attribute_name.hpp>
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#include <boost/log/attributes/attribute_value.hpp>
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#include <boost/log/attributes/attribute.hpp>
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#include <boost/log/attributes/attribute_value_set.hpp>
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#include <boost/log/attributes/value_visitation_fwd.hpp>
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#include <boost/log/attributes/fallback_policy.hpp>
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#include <boost/log/expressions/keyword_fwd.hpp>
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#include <boost/utility/explicit_operator_bool.hpp>
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#include <boost/log/utility/type_dispatch/static_type_dispatcher.hpp>
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#include <boost/log/detail/header.hpp>
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#ifdef BOOST_HAS_PRAGMA_ONCE
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#pragma once
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#endif
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namespace boost {
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BOOST_LOG_OPEN_NAMESPACE
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/*!
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* \brief The class represents attribute value visitation result
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*
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* The main purpose of this class is to provide a convenient interface for checking
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* whether the attribute value visitation succeeded or not. It also allows to discover
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* the actual cause of failure, should the operation fail.
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*/
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class visitation_result
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{
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public:
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//! Error codes for attribute value visitation
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enum error_code
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{
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ok, //!< The attribute value has been visited successfully
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value_not_found, //!< The attribute value is not present in the view
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value_has_invalid_type //!< The attribute value is present in the view, but has an unexpected type
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};
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private:
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error_code m_code;
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public:
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/*!
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* Initializing constructor. Creates the result that is equivalent to the
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* specified error code.
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*/
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BOOST_CONSTEXPR visitation_result(error_code code = ok) BOOST_NOEXCEPT : m_code(code) {}
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/*!
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* Checks if the visitation was successful.
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*
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* \return \c true if the value was visited successfully, \c false otherwise.
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*/
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BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT()
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/*!
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* Checks if the visitation was unsuccessful.
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*
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* \return \c false if the value was visited successfully, \c true otherwise.
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*/
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bool operator! () const BOOST_NOEXCEPT { return (m_code != ok); }
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/*!
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* \return The actual result code of value visitation
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*/
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error_code code() const BOOST_NOEXCEPT { return m_code; }
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};
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/*!
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* \brief Generic attribute value visitor invoker
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*
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* Attribute value invoker is a functional object that attempts to find and extract the stored
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* attribute value from the attribute value view or a log record. The extracted value is passed to
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* a unary function object (the visitor) provided by user.
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*
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* The invoker can be specialized on one or several attribute value types that should be
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* specified in the second template argument.
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*/
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template< typename T, typename FallbackPolicyT >
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class value_visitor_invoker :
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private FallbackPolicyT
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{
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typedef value_visitor_invoker< T, FallbackPolicyT > this_type;
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public:
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//! Attribute value types
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typedef T value_type;
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//! Fallback policy
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typedef FallbackPolicyT fallback_policy;
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//! Function object result type
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typedef visitation_result result_type;
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public:
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/*!
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* Default constructor
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*/
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BOOST_DEFAULTED_FUNCTION(value_visitor_invoker(), {})
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/*!
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* Copy constructor
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*/
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value_visitor_invoker(value_visitor_invoker const& that) : fallback_policy(static_cast< fallback_policy const& >(that))
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{
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}
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/*!
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* Initializing constructor
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*
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* \param arg Fallback policy argument
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*/
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template< typename U >
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explicit value_visitor_invoker(U const& arg) : fallback_policy(arg) {}
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/*!
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* Visitation operator. Attempts to acquire the stored value of one of the supported types. If acquisition succeeds,
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* the value is passed to \a visitor.
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*
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* \param attr An attribute value to apply the visitor to.
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* \param visitor A receiving function object to pass the attribute value to.
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* \return The result of visitation.
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*/
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template< typename VisitorT >
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result_type operator() (attribute_value const& attr, VisitorT visitor) const
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{
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if (!!attr)
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{
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static_type_dispatcher< value_type > disp(visitor);
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if (attr.dispatch(disp) || fallback_policy::apply_default(visitor))
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{
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return visitation_result::ok;
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}
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else
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{
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fallback_policy::on_invalid_type(attr.get_type());
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return visitation_result::value_has_invalid_type;
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}
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}
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if (fallback_policy::apply_default(visitor))
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return visitation_result::ok;
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fallback_policy::on_missing_value();
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return visitation_result::value_not_found;
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}
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/*!
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* Visitation operator. Looks for an attribute value with the specified name
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* and tries to acquire the stored value of one of the supported types. If acquisition succeeds,
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* the value is passed to \a visitor.
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*
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* \param name Attribute value name.
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* \param attrs A set of attribute values in which to look for the specified attribute value.
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* \param visitor A receiving function object to pass the attribute value to.
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* \return The result of visitation.
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*/
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template< typename VisitorT >
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result_type operator() (attribute_name const& name, attribute_value_set const& attrs, VisitorT visitor) const
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{
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try
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{
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attribute_value_set::const_iterator it = attrs.find(name);
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if (it != attrs.end())
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return operator() (it->second, visitor);
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else
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return operator() (attribute_value(), visitor);
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}
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catch (exception& e)
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{
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// Attach the attribute name to the exception
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boost::log::aux::attach_attribute_name_info(e, name);
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throw;
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}
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}
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/*!
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* Visitation operator. Looks for an attribute value with the specified name
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* and tries to acquire the stored value of one of the supported types. If acquisition succeeds,
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* the value is passed to \a visitor.
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*
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* \param name Attribute value name.
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* \param rec A log record. The attribute value will be sought among those associated with the record.
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* \param visitor A receiving function object to pass the attribute value to.
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* \return The result of visitation.
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*/
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template< typename VisitorT >
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result_type operator() (attribute_name const& name, record const& rec, VisitorT visitor) const
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{
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return operator() (name, rec.attribute_values(), visitor);
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}
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/*!
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* Visitation operator. Looks for an attribute value with the specified name
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* and tries to acquire the stored value of one of the supported types. If acquisition succeeds,
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* the value is passed to \a visitor.
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*
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* \param name Attribute value name.
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* \param rec A log record view. The attribute value will be sought among those associated with the record.
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* \param visitor A receiving function object to pass the attribute value to.
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* \return The result of visitation.
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*/
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template< typename VisitorT >
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result_type operator() (attribute_name const& name, record_view const& rec, VisitorT visitor) const
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{
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return operator() (name, rec.attribute_values(), visitor);
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}
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/*!
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* \returns Fallback policy
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*/
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fallback_policy const& get_fallback_policy() const
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{
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return *static_cast< fallback_policy const* >(this);
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}
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};
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/*!
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* The function applies a visitor to an attribute value from the view. The user has to explicitly specify the
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* type or set of possible types of the attribute value to be visited.
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*
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* \param name The name of the attribute value to visit.
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* \param attrs A set of attribute values in which to look for the specified attribute value.
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* \param visitor A receiving function object to pass the attribute value to.
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* \return The result of visitation.
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*/
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template< typename T, typename VisitorT >
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inline visitation_result
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visit(attribute_name const& name, attribute_value_set const& attrs, VisitorT visitor)
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{
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value_visitor_invoker< T > invoker;
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return invoker(name, attrs, visitor);
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}
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/*!
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* The function applies a visitor to an attribute value from the view. The user has to explicitly specify the
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* type or set of possible types of the attribute value to be visited.
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*
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* \param name The name of the attribute value to visit.
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* \param rec A log record. The attribute value will be sought among those associated with the record.
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* \param visitor A receiving function object to pass the attribute value to.
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* \return The result of visitation.
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*/
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template< typename T, typename VisitorT >
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inline visitation_result
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visit(attribute_name const& name, record const& rec, VisitorT visitor)
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{
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value_visitor_invoker< T > invoker;
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return invoker(name, rec, visitor);
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}
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/*!
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* The function applies a visitor to an attribute value from the view. The user has to explicitly specify the
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* type or set of possible types of the attribute value to be visited.
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*
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* \param name The name of the attribute value to visit.
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* \param rec A log record view. The attribute value will be sought among those associated with the record.
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* \param visitor A receiving function object to pass the attribute value to.
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* \return The result of visitation.
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*/
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template< typename T, typename VisitorT >
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inline visitation_result
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visit(attribute_name const& name, record_view const& rec, VisitorT visitor)
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{
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value_visitor_invoker< T > invoker;
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return invoker(name, rec, visitor);
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}
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/*!
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* The function applies a visitor to an attribute value. The user has to explicitly specify the
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* type or set of possible types of the attribute value to be visited.
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*
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* \param value The attribute value to visit.
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* \param visitor A receiving function object to pass the attribute value to.
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* \return The result of visitation.
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*/
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template< typename T, typename VisitorT >
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inline visitation_result
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visit(attribute_value const& value, VisitorT visitor)
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{
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value_visitor_invoker< T > invoker;
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return invoker(value, visitor);
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}
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/*!
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* The function applies a visitor to an attribute value from the view. The user has to explicitly specify the
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* type or set of possible types of the attribute value to be visited.
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*
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* \param keyword The keyword of the attribute value to visit.
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* \param attrs A set of attribute values in which to look for the specified attribute value.
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* \param visitor A receiving function object to pass the attribute value to.
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* \return The result of visitation.
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*/
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template< typename DescriptorT, template< typename > class ActorT, typename VisitorT >
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inline visitation_result
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visit(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, attribute_value_set const& attrs, VisitorT visitor)
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{
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value_visitor_invoker< typename DescriptorT::value_type > invoker;
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return invoker(keyword.get_name(), attrs, visitor);
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}
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/*!
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* The function applies a visitor to an attribute value from the view. The user has to explicitly specify the
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* type or set of possible types of the attribute value to be visited.
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*
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* \param keyword The keyword of the attribute value to visit.
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* \param rec A log record. The attribute value will be sought among those associated with the record.
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* \param visitor A receiving function object to pass the attribute value to.
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* \return The result of visitation.
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*/
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template< typename DescriptorT, template< typename > class ActorT, typename VisitorT >
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inline visitation_result
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visit(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, record const& rec, VisitorT visitor)
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{
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value_visitor_invoker< typename DescriptorT::value_type > invoker;
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return invoker(keyword.get_name(), rec, visitor);
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}
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/*!
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* The function applies a visitor to an attribute value from the view. The user has to explicitly specify the
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* type or set of possible types of the attribute value to be visited.
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*
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* \param keyword The keyword of the attribute value to visit.
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* \param rec A log record view. The attribute value will be sought among those associated with the record.
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* \param visitor A receiving function object to pass the attribute value to.
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* \return The result of visitation.
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*/
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template< typename DescriptorT, template< typename > class ActorT, typename VisitorT >
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inline visitation_result
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visit(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, record_view const& rec, VisitorT visitor)
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{
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value_visitor_invoker< typename DescriptorT::value_type > invoker;
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return invoker(keyword.get_name(), rec, visitor);
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}
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#if !defined(BOOST_LOG_DOXYGEN_PASS)
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template< typename T, typename VisitorT >
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inline visitation_result attribute_value::visit(VisitorT visitor) const
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{
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return boost::log::visit< T >(*this, visitor);
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}
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#endif // !defined(BOOST_LOG_DOXYGEN_PASS)
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BOOST_LOG_CLOSE_NAMESPACE // namespace log
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} // namespace boost
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#include <boost/log/detail/footer.hpp>
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#endif // BOOST_LOG_ATTRIBUTES_VALUE_VISITATION_HPP_INCLUDED_
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