boost/log/attributes/value_extraction.hpp
/* * Copyright Andrey Semashev 2007 - 2015. * Distributed under the Boost Software License, Version 1.0. * (See accompanying file LICENSE_1_0.txt or copy at * http://www.boost.org/LICENSE_1_0.txt) */ /*! * \file value_extraction.hpp * \author Andrey Semashev * \date 01.03.2008 * * The header contains implementation of tools for extracting an attribute value * from the view. */ #ifndef BOOST_LOG_ATTRIBUTES_VALUE_EXTRACTION_HPP_INCLUDED_ #define BOOST_LOG_ATTRIBUTES_VALUE_EXTRACTION_HPP_INCLUDED_ #include <boost/mpl/vector.hpp> #include <boost/mpl/joint_view.hpp> #include <boost/mpl/if.hpp> #include <boost/mpl/eval_if.hpp> #include <boost/mpl/identity.hpp> #include <boost/mpl/is_sequence.hpp> #include <boost/mpl/contains.hpp> #include <boost/mpl/push_back.hpp> #include <boost/type_traits/is_same.hpp> #include <boost/core/enable_if.hpp> #include <boost/log/detail/config.hpp> #include <boost/log/exceptions.hpp> #include <boost/log/core/record.hpp> #include <boost/log/attributes/attribute_name.hpp> #include <boost/log/attributes/attribute_value.hpp> #include <boost/log/attributes/attribute.hpp> #include <boost/log/attributes/attribute_value_set.hpp> #include <boost/log/attributes/value_extraction_fwd.hpp> #include <boost/log/attributes/fallback_policy.hpp> #include <boost/log/expressions/keyword_fwd.hpp> #include <boost/log/utility/value_ref.hpp> #include <boost/log/utility/type_dispatch/static_type_dispatcher.hpp> #include <boost/log/detail/header.hpp> #ifdef BOOST_HAS_PRAGMA_ONCE #pragma once #endif namespace boost { BOOST_LOG_OPEN_NAMESPACE namespace result_of { /*! * \brief A metafunction that allows to acquire the result of the value extraction * * The metafunction results in a type that is in form of <tt>T const&</tt>, if \c T is * not an MPL type sequence and <tt>DefaultT</tt> is the same as <tt>T</tt>, * or <tt>value_ref< TypesT, TagT ></tt> otherwise, with * \c TypesT being a type sequence comprising the types from sequence \c T and \c DefaultT, * if it is not present in \c T already. */ template< typename T, typename DefaultT, typename TagT > struct extract_or_default { typedef typename mpl::eval_if< mpl::is_sequence< T >, mpl::eval_if< mpl::contains< T, DefaultT >, mpl::identity< T >, mpl::push_back< T, DefaultT > >, mpl::if_< is_same< T, DefaultT >, T, mpl::vector2< T, DefaultT > > >::type extracted_type; typedef typename mpl::if_< mpl::is_sequence< extracted_type >, value_ref< extracted_type, TagT >, extracted_type const& >::type type; }; /*! * \brief A metafunction that allows to acquire the result of the value extraction * * The metafunction results in a type that is in form of <tt>T const&</tt>, if \c T is * not an MPL type sequence, or <tt>value_ref< T, TagT ></tt> otherwise. In the latter * case the value reference shall never be empty. */ template< typename T, typename TagT > struct extract_or_throw { typedef typename mpl::if_< mpl::is_sequence< T >, value_ref< T, TagT >, T const& >::type type; }; /*! * \brief A metafunction that allows to acquire the result of the value extraction * * The metafunction results in a type that is in form of <tt>value_ref< T, TagT ></tt>. */ template< typename T, typename TagT > struct extract { typedef value_ref< T, TagT > type; }; } // namespace result_of namespace aux { //! The function object initializes the value reference template< typename RefT > struct value_ref_initializer { typedef void result_type; value_ref_initializer(RefT& ref) : m_ref(ref) { } template< typename ArgT > result_type operator() (ArgT const& arg) const { m_ref = RefT(arg); } private: RefT& m_ref; }; //! The function unwraps \c value_ref, if possible template< typename T, typename TagT > BOOST_FORCEINLINE typename boost::enable_if_c< mpl::is_sequence< T >::value, value_ref< T, TagT > >::type unwrap_value_ref(value_ref< T, TagT > const& r) { return r; } template< typename T, typename TagT > BOOST_FORCEINLINE typename boost::disable_if_c< mpl::is_sequence< T >::value, T const& >::type unwrap_value_ref(value_ref< T, TagT > const& r) { return r.get(); } } // namespace aux /*! * \brief Generic attribute value extractor * * Attribute value extractor is a functional object that attempts to find and extract the stored * attribute value from the attribute values view or a log record. The extracted value is returned * from the extractor. */ template< typename T, typename FallbackPolicyT, typename TagT > class value_extractor : private FallbackPolicyT { public: //! Fallback policy typedef FallbackPolicyT fallback_policy; //! Attribute value types typedef T value_type; //! Function object result type typedef value_ref< value_type, TagT > result_type; public: /*! * Default constructor */ BOOST_DEFAULTED_FUNCTION(value_extractor(), {}) /*! * Copy constructor */ value_extractor(value_extractor const& that) : fallback_policy(static_cast< fallback_policy const& >(that)) { } /*! * Constructor * * \param arg Fallback policy constructor argument */ template< typename U > explicit value_extractor(U const& arg) : fallback_policy(arg) {} /*! * Extraction operator. Attempts to acquire the stored value of one of the supported types. If extraction succeeds, * the extracted value is returned. * * \param attr The attribute value to extract from. * \return The extracted value, if extraction succeeded, an empty value otherwise. */ result_type operator() (attribute_value const& attr) const { result_type res; aux::value_ref_initializer< result_type > initializer(res); if (!!attr) { static_type_dispatcher< value_type > disp(initializer); if (!attr.dispatch(disp) && !fallback_policy::apply_default(initializer)) fallback_policy::on_invalid_type(attr.get_type()); } else if (!fallback_policy::apply_default(initializer)) { fallback_policy::on_missing_value(); } return res; } /*! * Extraction operator. Looks for an attribute value with the specified name * and tries to acquire the stored value of one of the supported types. If extraction succeeds, * the extracted value is returned. * * \param name Attribute value name. * \param attrs A set of attribute values in which to look for the specified attribute value. * \return The extracted value, if extraction succeeded, an empty value otherwise. */ result_type operator() (attribute_name const& name, attribute_value_set const& attrs) const { try { attribute_value_set::const_iterator it = attrs.find(name); if (it != attrs.end()) return operator() (it->second); else return operator() (attribute_value()); } catch (exception& e) { // Attach the attribute name to the exception boost::log::aux::attach_attribute_name_info(e, name); throw; } } /*! * Extraction operator. Looks for an attribute value with the specified name * and tries to acquire the stored value of one of the supported types. If extraction succeeds, * the extracted value is returned. * * \param name Attribute value name. * \param rec A log record. The attribute value will be sought among those associated with the record. * \return The extracted value, if extraction succeeded, an empty value otherwise. */ result_type operator() (attribute_name const& name, record const& rec) const { return operator() (name, rec.attribute_values()); } /*! * Extraction operator. Looks for an attribute value with the specified name * and tries to acquire the stored value of one of the supported types. If extraction succeeds, * the extracted value is returned. * * \param name Attribute value name. * \param rec A log record view. The attribute value will be sought among those associated with the record. * \return The extracted value, if extraction succeeded, an empty value otherwise. */ result_type operator() (attribute_name const& name, record_view const& rec) const { return operator() (name, rec.attribute_values()); } /*! * \returns Fallback policy */ fallback_policy const& get_fallback_policy() const { return *static_cast< fallback_policy const* >(this); } }; #if !defined(BOOST_LOG_DOXYGEN_PASS) #if !defined(BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS) #define BOOST_LOG_AUX_VOID_DEFAULT = void #else #define BOOST_LOG_AUX_VOID_DEFAULT #endif #endif // !defined(BOOST_LOG_DOXYGEN_PASS) /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param name The name of the attribute value to extract. * \param attrs A set of attribute values in which to look for the specified attribute value. * \return A \c value_ref that refers to the extracted value, if found. An empty value otherwise. */ template< typename T, typename TagT BOOST_LOG_AUX_VOID_DEFAULT > inline typename result_of::extract< T, TagT >::type extract(attribute_name const& name, attribute_value_set const& attrs) { value_extractor< T, fallback_to_none, TagT > extractor; return extractor(name, attrs); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param name The name of the attribute value to extract. * \param rec A log record. The attribute value will be sought among those associated with the record. * \return A \c value_ref that refers to the extracted value, if found. An empty value otherwise. */ template< typename T, typename TagT BOOST_LOG_AUX_VOID_DEFAULT > inline typename result_of::extract< T, TagT >::type extract(attribute_name const& name, record const& rec) { value_extractor< T, fallback_to_none, TagT > extractor; return extractor(name, rec); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param name The name of the attribute value to extract. * \param rec A log record view. The attribute value will be sought among those associated with the record. * \return A \c value_ref that refers to the extracted value, if found. An empty value otherwise. */ template< typename T, typename TagT BOOST_LOG_AUX_VOID_DEFAULT > inline typename result_of::extract< T, TagT >::type extract(attribute_name const& name, record_view const& rec) { value_extractor< T, fallback_to_none, TagT > extractor; return extractor(name, rec); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param value Attribute value. * \return A \c value_ref that refers to the extracted value, if found. An empty value otherwise. */ template< typename T, typename TagT BOOST_LOG_AUX_VOID_DEFAULT > inline typename result_of::extract< T, TagT >::type extract(attribute_value const& value) { value_extractor< T, fallback_to_none, TagT > extractor; return extractor(value); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param name The name of the attribute value to extract. * \param attrs A set of attribute values in which to look for the specified attribute value. * \return The extracted value or a non-empty \c value_ref that refers to the value. * \throws An exception is thrown if the requested value cannot be extracted. */ template< typename T, typename TagT BOOST_LOG_AUX_VOID_DEFAULT > inline typename result_of::extract_or_throw< T, TagT >::type extract_or_throw(attribute_name const& name, attribute_value_set const& attrs) { value_extractor< T, fallback_to_throw, TagT > extractor; return aux::unwrap_value_ref(extractor(name, attrs)); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param name The name of the attribute value to extract. * \param rec A log record. The attribute value will be sought among those associated with the record. * \return The extracted value or a non-empty \c value_ref that refers to the value. * \throws An exception is thrown if the requested value cannot be extracted. */ template< typename T, typename TagT BOOST_LOG_AUX_VOID_DEFAULT > inline typename result_of::extract_or_throw< T, TagT >::type extract_or_throw(attribute_name const& name, record const& rec) { value_extractor< T, fallback_to_throw, TagT > extractor; return aux::unwrap_value_ref(extractor(name, rec)); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param name The name of the attribute value to extract. * \param rec A log record view. The attribute value will be sought among those associated with the record. * \return The extracted value or a non-empty \c value_ref that refers to the value. * \throws An exception is thrown if the requested value cannot be extracted. */ template< typename T, typename TagT BOOST_LOG_AUX_VOID_DEFAULT > inline typename result_of::extract_or_throw< T, TagT >::type extract_or_throw(attribute_name const& name, record_view const& rec) { value_extractor< T, fallback_to_throw, TagT > extractor; return aux::unwrap_value_ref(extractor(name, rec)); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param value Attribute value. * \return The extracted value or a non-empty \c value_ref that refers to the value. * \throws An exception is thrown if the requested value cannot be extracted. */ template< typename T, typename TagT BOOST_LOG_AUX_VOID_DEFAULT > inline typename result_of::extract_or_throw< T, TagT >::type extract_or_throw(attribute_value const& value) { value_extractor< T, fallback_to_throw, TagT > extractor; return aux::unwrap_value_ref(extractor(value)); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \note Caution must be exercised if the default value is a temporary object. Because the function returns * a reference, if the temporary object is destroyed, the reference may become dangling. * * \param name The name of the attribute value to extract. * \param attrs A set of attribute values in which to look for the specified attribute value. * \param def_val The default value * \return The extracted value, if found. The default value otherwise. */ template< typename T, typename TagT BOOST_LOG_AUX_VOID_DEFAULT, typename DefaultT > inline typename result_of::extract_or_default< T, DefaultT, TagT >::type extract_or_default(attribute_name const& name, attribute_value_set const& attrs, DefaultT const& def_val) { typedef typename result_of::extract_or_default< T, DefaultT, TagT >::extracted_type extracted_type; value_extractor< extracted_type, fallback_to_default< DefaultT const& >, TagT > extractor(def_val); return aux::unwrap_value_ref(extractor(name, attrs)); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be visited. * * \note Caution must be exercised if the default value is a temporary object. Because the function returns * a reference, if the temporary object is destroyed, the reference may become dangling. * * \param name The name of the attribute value to extract. * \param rec A log record. The attribute value will be sought among those associated with the record. * \param def_val The default value * \return The extracted value, if found. The default value otherwise. */ template< typename T, typename TagT BOOST_LOG_AUX_VOID_DEFAULT, typename DefaultT > inline typename result_of::extract_or_default< T, DefaultT, TagT >::type extract_or_default(attribute_name const& name, record const& rec, DefaultT const& def_val) { typedef typename result_of::extract_or_default< T, DefaultT, TagT >::extracted_type extracted_type; value_extractor< extracted_type, fallback_to_default< DefaultT const& >, TagT > extractor(def_val); return aux::unwrap_value_ref(extractor(name, rec)); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be visited. * * \note Caution must be exercised if the default value is a temporary object. Because the function returns * a reference, if the temporary object is destroyed, the reference may become dangling. * * \param name The name of the attribute value to extract. * \param rec A log record view. The attribute value will be sought among those associated with the record. * \param def_val The default value * \return The extracted value, if found. The default value otherwise. */ template< typename T, typename TagT BOOST_LOG_AUX_VOID_DEFAULT, typename DefaultT > inline typename result_of::extract_or_default< T, DefaultT, TagT >::type extract_or_default(attribute_name const& name, record_view const& rec, DefaultT const& def_val) { typedef typename result_of::extract_or_default< T, DefaultT, TagT >::extracted_type extracted_type; value_extractor< extracted_type, fallback_to_default< DefaultT const& >, TagT > extractor(def_val); return aux::unwrap_value_ref(extractor(name, rec)); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be visited. * * \note Caution must be exercised if the default value is a temporary object. Because the function returns * a reference, if the temporary object is destroyed, the reference may become dangling. * * \param value Attribute value. * \param def_val The default value * \return The extracted value, if found. The default value otherwise. */ template< typename T, typename TagT BOOST_LOG_AUX_VOID_DEFAULT, typename DefaultT > inline typename result_of::extract_or_default< T, DefaultT, TagT >::type extract_or_default(attribute_value const& value, DefaultT const& def_val) { typedef typename result_of::extract_or_default< T, DefaultT, TagT >::extracted_type extracted_type; value_extractor< extracted_type, fallback_to_default< DefaultT const& >, TagT > extractor(def_val); return aux::unwrap_value_ref(extractor(value)); } #if defined(BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS) template< typename T > inline typename result_of::extract< T >::type extract(attribute_name const& name, attribute_value_set const& attrs) { value_extractor< T, fallback_to_none > extractor; return extractor(name, attrs); } template< typename T > inline typename result_of::extract< T >::type extract(attribute_name const& name, record const& rec) { value_extractor< T, fallback_to_none > extractor; return extractor(name, rec); } template< typename T > inline typename result_of::extract< T >::type extract(attribute_name const& name, record_view const& rec) { value_extractor< T, fallback_to_none > extractor; return extractor(name, rec); } template< typename T > inline typename result_of::extract< T >::type extract(attribute_value const& value) { value_extractor< T, fallback_to_none > extractor; return extractor(value); } template< typename T > inline typename result_of::extract_or_throw< T >::type extract_or_throw(attribute_name const& name, attribute_value_set const& attrs) { value_extractor< T, fallback_to_throw > extractor; return aux::unwrap_value_ref(extractor(name, attrs)); } template< typename T > inline typename result_of::extract_or_throw< T >::type extract_or_throw(attribute_name const& name, record const& rec) { value_extractor< T, fallback_to_throw > extractor; return aux::unwrap_value_ref(extractor(name, rec)); } template< typename T > inline typename result_of::extract_or_throw< T >::type extract_or_throw(attribute_name const& name, record_view const& rec) { value_extractor< T, fallback_to_throw > extractor; return aux::unwrap_value_ref(extractor(name, rec)); } template< typename T > inline typename result_of::extract_or_throw< T >::type extract_or_throw(attribute_value const& value) { value_extractor< T, fallback_to_throw > extractor; return aux::unwrap_value_ref(extractor(value)); } template< typename T, typename DefaultT > inline typename result_of::extract_or_default< T, DefaultT >::type extract_or_default( attribute_name const& name, attribute_value_set const& attrs, DefaultT const& def_val) { typedef typename result_of::extract_or_default< T, DefaultT >::extracted_type extracted_type; value_extractor< extracted_type, fallback_to_default< DefaultT const& > > extractor(def_val); return aux::unwrap_value_ref(extractor(name, attrs)); } template< typename T, typename DefaultT > inline typename result_of::extract_or_default< T, DefaultT >::type extract_or_default( attribute_name const& name, record const& rec, DefaultT const& def_val) { typedef typename result_of::extract_or_default< T, DefaultT >::extracted_type extracted_type; value_extractor< extracted_type, fallback_to_default< DefaultT const& > > extractor(def_val); return aux::unwrap_value_ref(extractor(name, rec)); } template< typename T, typename DefaultT > inline typename result_of::extract_or_default< T, DefaultT >::type extract_or_default( attribute_name const& name, record_view const& rec, DefaultT const& def_val) { typedef typename result_of::extract_or_default< T, DefaultT >::extracted_type extracted_type; value_extractor< extracted_type, fallback_to_default< DefaultT const& > > extractor(def_val); return aux::unwrap_value_ref(extractor(name, rec)); } template< typename T, typename DefaultT > inline typename result_of::extract_or_default< T, DefaultT >::type extract_or_default(attribute_value const& value, DefaultT const& def_val) { typedef typename result_of::extract_or_default< T, DefaultT >::extracted_type extracted_type; value_extractor< extracted_type, fallback_to_default< DefaultT const& > > extractor(def_val); return aux::unwrap_value_ref(extractor(value)); } #endif // defined(BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS) /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param keyword The keyword of the attribute value to extract. * \param attrs A set of attribute values in which to look for the specified attribute value. * \return A \c value_ref that refers to the extracted value, if found. An empty value otherwise. */ template< typename DescriptorT, template< typename > class ActorT > inline typename result_of::extract< typename DescriptorT::value_type, DescriptorT >::type extract(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, attribute_value_set const& attrs) { value_extractor< typename DescriptorT::value_type, fallback_to_none, DescriptorT > extractor; return extractor(keyword.get_name(), attrs); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param keyword The keyword of the attribute value to extract. * \param rec A log record. The attribute value will be sought among those associated with the record. * \return A \c value_ref that refers to the extracted value, if found. An empty value otherwise. */ template< typename DescriptorT, template< typename > class ActorT > inline typename result_of::extract< typename DescriptorT::value_type, DescriptorT >::type extract(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, record const& rec) { value_extractor< typename DescriptorT::value_type, fallback_to_none, DescriptorT > extractor; return extractor(keyword.get_name(), rec); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param keyword The keyword of the attribute value to extract. * \param rec A log record view. The attribute value will be sought among those associated with the record. * \return A \c value_ref that refers to the extracted value, if found. An empty value otherwise. */ template< typename DescriptorT, template< typename > class ActorT > inline typename result_of::extract< typename DescriptorT::value_type, DescriptorT >::type extract(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, record_view const& rec) { value_extractor< typename DescriptorT::value_type, fallback_to_none, DescriptorT > extractor; return extractor(keyword.get_name(), rec); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param keyword The keyword of the attribute value to extract. * \param attrs A set of attribute values in which to look for the specified attribute value. * \return The extracted value or a non-empty \c value_ref that refers to the value. * \throws An exception is thrown if the requested value cannot be extracted. */ template< typename DescriptorT, template< typename > class ActorT > inline typename result_of::extract_or_throw< typename DescriptorT::value_type, DescriptorT >::type extract_or_throw(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, attribute_value_set const& attrs) { value_extractor< typename DescriptorT::value_type, fallback_to_throw, DescriptorT > extractor; return aux::unwrap_value_ref(extractor(keyword.get_name(), attrs)); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param keyword The keyword of the attribute value to extract. * \param rec A log record. The attribute value will be sought among those associated with the record. * \return The extracted value or a non-empty \c value_ref that refers to the value. * \throws An exception is thrown if the requested value cannot be extracted. */ template< typename DescriptorT, template< typename > class ActorT > inline typename result_of::extract_or_throw< typename DescriptorT::value_type, DescriptorT >::type extract_or_throw(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, record const& rec) { value_extractor< typename DescriptorT::value_type, fallback_to_throw, DescriptorT > extractor; return aux::unwrap_value_ref(extractor(keyword.get_name(), rec)); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \param keyword The keyword of the attribute value to extract. * \param rec A log record view. The attribute value will be sought among those associated with the record. * \return The extracted value or a non-empty \c value_ref that refers to the value. * \throws An exception is thrown if the requested value cannot be extracted. */ template< typename DescriptorT, template< typename > class ActorT > inline typename result_of::extract_or_throw< typename DescriptorT::value_type, DescriptorT >::type extract_or_throw(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, record_view const& rec) { value_extractor< typename DescriptorT::value_type, fallback_to_throw, DescriptorT > extractor; return aux::unwrap_value_ref(extractor(keyword.get_name(), rec)); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be extracted. * * \note Caution must be exercised if the default value is a temporary object. Because the function returns * a reference, if the temporary object is destroyed, the reference may become dangling. * * \param keyword The keyword of the attribute value to extract. * \param attrs A set of attribute values in which to look for the specified attribute value. * \param def_val The default value * \return The extracted value, if found. The default value otherwise. */ template< typename DescriptorT, template< typename > class ActorT, typename DefaultT > inline typename result_of::extract_or_default< typename DescriptorT::value_type, DefaultT, DescriptorT >::type extract_or_default(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, attribute_value_set const& attrs, DefaultT const& def_val) { typedef typename result_of::extract_or_default< typename DescriptorT::value_type, DefaultT, DescriptorT >::extracted_type extracted_type; value_extractor< extracted_type, fallback_to_default< DefaultT const& >, DescriptorT > extractor(def_val); return aux::unwrap_value_ref(extractor(keyword.get_name(), attrs)); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be visited. * * \note Caution must be exercised if the default value is a temporary object. Because the function returns * a reference, if the temporary object is destroyed, the reference may become dangling. * * \param keyword The keyword of the attribute value to extract. * \param rec A log record. The attribute value will be sought among those associated with the record. * \param def_val The default value * \return The extracted value, if found. The default value otherwise. */ template< typename DescriptorT, template< typename > class ActorT, typename DefaultT > inline typename result_of::extract_or_default< typename DescriptorT::value_type, DefaultT, DescriptorT >::type extract_or_default(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, record const& rec, DefaultT const& def_val) { typedef typename result_of::extract_or_default< typename DescriptorT::value_type, DefaultT, DescriptorT >::extracted_type extracted_type; value_extractor< extracted_type, fallback_to_default< DefaultT const& >, DescriptorT > extractor(def_val); return aux::unwrap_value_ref(extractor(keyword.get_name(), rec)); } /*! * The function extracts an attribute value from the view. The user has to explicitly specify the * type or set of possible types of the attribute value to be visited. * * \note Caution must be exercised if the default value is a temporary object. Because the function returns * a reference, if the temporary object is destroyed, the reference may become dangling. * * \param keyword The keyword of the attribute value to extract. * \param rec A log record view. The attribute value will be sought among those associated with the record. * \param def_val The default value * \return The extracted value, if found. The default value otherwise. */ template< typename DescriptorT, template< typename > class ActorT, typename DefaultT > inline typename result_of::extract_or_default< typename DescriptorT::value_type, DefaultT, DescriptorT >::type extract_or_default(expressions::attribute_keyword< DescriptorT, ActorT > const& keyword, record_view const& rec, DefaultT const& def_val) { typedef typename result_of::extract_or_default< typename DescriptorT::value_type, DefaultT, DescriptorT >::extracted_type extracted_type; value_extractor< extracted_type, fallback_to_default< DefaultT const& >, DescriptorT > extractor(def_val); return aux::unwrap_value_ref(extractor(keyword.get_name(), rec)); } #if !defined(BOOST_LOG_DOXYGEN_PASS) template< typename T, typename TagT > inline typename result_of::extract< T, TagT >::type attribute_value::extract() const { return boost::log::extract< T, TagT >(*this); } template< typename T, typename TagT > inline typename result_of::extract_or_throw< T, TagT >::type attribute_value::extract_or_throw() const { return boost::log::extract_or_throw< T, TagT >(*this); } template< typename T, typename TagT > inline typename result_of::extract_or_default< T, T, TagT >::type attribute_value::extract_or_default(T const& def_value) const { return boost::log::extract_or_default< T, TagT >(*this, def_value); } template< typename T, typename TagT, typename DefaultT > inline typename result_of::extract_or_default< T, DefaultT, TagT >::type attribute_value::extract_or_default(DefaultT const& def_value) const { return boost::log::extract_or_default< T, TagT >(*this, def_value); } #if defined(BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS) template< typename T > inline typename result_of::extract< T >::type attribute_value::extract() const { return boost::log::extract< T >(*this); } template< typename T > inline typename result_of::extract_or_throw< T >::type attribute_value::extract_or_throw() const { return boost::log::extract_or_throw< T >(*this); } template< typename T > inline typename result_of::extract_or_default< T, T >::type attribute_value::extract_or_default(T const& def_value) const { return boost::log::extract_or_default< T >(*this, def_value); } template< typename T, typename DefaultT > inline typename result_of::extract_or_default< T, DefaultT >::type attribute_value::extract_or_default(DefaultT const& def_value) const { return boost::log::extract_or_default< T >(*this, def_value); } #endif // defined(BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS) #endif // !defined(BOOST_LOG_DOXYGEN_PASS) #undef BOOST_LOG_AUX_VOID_DEFAULT BOOST_LOG_CLOSE_NAMESPACE // namespace log } // namespace boost #include <boost/log/detail/footer.hpp> #endif // BOOST_LOG_ATTRIBUTES_VALUE_EXTRACTION_HPP_INCLUDED_