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