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+/*
+ *          Copyright Andrey Semashev 2007 - 2014.
+ * 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   has_attr.hpp
+ * \author Andrey Semashev
+ * \date   23.07.2012
+ *
+ * The header contains implementation of a generic attribute presence checker in template expressions.
+ */
+
+#ifndef BOOST_LOG_EXPRESSIONS_PREDICATES_HAS_ATTR_HPP_INCLUDED_
+#define BOOST_LOG_EXPRESSIONS_PREDICATES_HAS_ATTR_HPP_INCLUDED_
+
+#include <boost/phoenix/core/actor.hpp>
+#include <boost/log/detail/config.hpp>
+#include <boost/log/core/record_view.hpp>
+#include <boost/log/attributes/attribute_name.hpp>
+#include <boost/log/attributes/attribute_value_set.hpp>
+#include <boost/log/attributes/value_visitation.hpp>
+#include <boost/log/expressions/keyword_fwd.hpp>
+#include <boost/log/detail/unary_function_terminal.hpp>
+#include <boost/log/utility/functional/nop.hpp>
+#include <boost/log/detail/header.hpp>
+
+#ifdef BOOST_HAS_PRAGMA_ONCE
+#pragma once
+#endif
+
+namespace boost {
+
+BOOST_LOG_OPEN_NAMESPACE
+
+namespace expressions {
+
+/*!
+ * An attribute value presence checker.
+ */
+template< typename T >
+class has_attribute
+{
+public:
+    //! Function result_type
+    typedef bool result_type;
+    //! Expected attribute value type
+    typedef T value_type;
+
+private:
+    //! Attribute value name
+    const attribute_name m_name;
+    //! Visitor invoker
+    value_visitor_invoker< value_type > m_visitor_invoker;
+
+public:
+    /*!
+     * Initializing constructor
+     *
+     * \param name Attribute name
+     */
+    explicit has_attribute(attribute_name const& name) : m_name(name)
+    {
+    }
+
+    /*!
+     * Checking operator
+     *
+     * \param arg A set of attribute values or a log record
+     * \return \c true if the log record contains the sought attribute value, \c false otherwise
+     */
+    template< typename ArgT >
+    result_type operator() (ArgT const& arg) const
+    {
+        return m_visitor_invoker(m_name, arg, nop()).code() == visitation_result::ok;
+    }
+};
+
+/*!
+ * An attribute value presence checker. This specialization does not check the type of the attribute value.
+ */
+template< >
+class has_attribute< void >
+{
+public:
+    //! Function result_type
+    typedef bool result_type;
+    //! Expected attribute value type
+    typedef void value_type;
+
+private:
+    //! Attribute name
+    const attribute_name m_name;
+
+public:
+    /*!
+     * Initializing constructor
+     *
+     * \param name Attribute name
+     */
+    explicit has_attribute(attribute_name const& name) : m_name(name)
+    {
+    }
+
+    /*!
+     * Checking operator
+     *
+     * \param attrs A set of attribute values
+     * \return \c true if the log record contains the sought attribute value, \c false otherwise
+     */
+    result_type operator() (attribute_value_set const& attrs) const
+    {
+        return attrs.find(m_name) != attrs.end();
+    }
+
+    /*!
+     * Checking operator
+     *
+     * \param rec A log record
+     * \return \c true if the log record contains the sought attribute value, \c false otherwise
+     */
+    result_type operator() (boost::log::record_view const& rec) const
+    {
+        return operator()(rec.attribute_values());
+    }
+};
+
+/*!
+ * The function generates a terminal node in a template expression. The node will check for the attribute value
+ * presence in a log record. The node will also check that the attribute value has the specified type, if present.
+ */
+template< typename AttributeValueT >
+BOOST_FORCEINLINE phoenix::actor< aux::unary_function_terminal< has_attribute< AttributeValueT > > > has_attr(attribute_name const& name)
+{
+    typedef aux::unary_function_terminal< has_attribute< AttributeValueT > > terminal_type;
+    phoenix::actor< terminal_type > act = {{ terminal_type(name) }};
+    return act;
+}
+
+/*!
+ * The function generates a terminal node in a template expression. The node will check for the attribute value
+ * presence in a log record.
+ */
+BOOST_FORCEINLINE phoenix::actor< aux::unary_function_terminal< has_attribute< void > > > has_attr(attribute_name const& name)
+{
+    typedef aux::unary_function_terminal< has_attribute< void > > terminal_type;
+    phoenix::actor< terminal_type > act = {{ terminal_type(name) }};
+    return act;
+}
+
+/*!
+ * The function generates a terminal node in a template expression. The node will check for the attribute value
+ * presence in a log record. The node will also check that the attribute value has the specified type, if present.
+ */
+template< typename DescriptorT, template< typename > class ActorT >
+BOOST_FORCEINLINE ActorT< aux::unary_function_terminal< has_attribute< typename DescriptorT::value_type > > > has_attr(attribute_keyword< DescriptorT, ActorT > const&)
+{
+    typedef aux::unary_function_terminal< has_attribute< typename DescriptorT::value_type > > terminal_type;
+    ActorT< terminal_type > act = {{ terminal_type(DescriptorT::get_name()) }};
+    return act;
+}
+
+} // namespace expressions
+
+BOOST_LOG_CLOSE_NAMESPACE // namespace log
+
+} // namespace boost
+
+#include <boost/log/detail/footer.hpp>
+
+#endif // BOOST_LOG_EXPRESSIONS_PREDICATES_HAS_ATTR_HPP_INCLUDED_