Chris@16: /*
Chris@101:  *          Copyright Andrey Semashev 2007 - 2015.
Chris@16:  * Distributed under the Boost Software License, Version 1.0.
Chris@16:  *    (See accompanying file LICENSE_1_0.txt or copy at
Chris@16:  *          http://www.boost.org/LICENSE_1_0.txt)
Chris@16:  */
Chris@16: /*!
Chris@16:  * \file   fallback_policy.hpp
Chris@16:  * \author Andrey Semashev
Chris@16:  * \date   18.08.2012
Chris@16:  *
Chris@16:  * The header contains definition of fallback policies when attribute value visitation or extraction fails.
Chris@16:  */
Chris@16: 
Chris@16: #ifndef BOOST_LOG_ATTRIBUTES_FALLBACK_POLICY_HPP_INCLUDED_
Chris@16: #define BOOST_LOG_ATTRIBUTES_FALLBACK_POLICY_HPP_INCLUDED_
Chris@16: 
Chris@16: #include <boost/type_traits/remove_cv.hpp>
Chris@16: #include <boost/type_traits/remove_reference.hpp>
Chris@16: #include <boost/log/detail/config.hpp>
Chris@16: #include <boost/log/exceptions.hpp>
Chris@16: #include <boost/log/utility/type_info_wrapper.hpp>
Chris@16: #include <boost/log/attributes/fallback_policy_fwd.hpp>
Chris@16: #include <boost/log/detail/header.hpp>
Chris@16: 
Chris@16: #ifdef BOOST_HAS_PRAGMA_ONCE
Chris@16: #pragma once
Chris@16: #endif
Chris@16: 
Chris@16: namespace boost {
Chris@16: 
Chris@16: BOOST_LOG_OPEN_NAMESPACE
Chris@16: 
Chris@16: /*!
Chris@16:  * The \c fallback_to_none policy results in returning an empty value reference if the attribute value cannot be extracted.
Chris@16:  */
Chris@16: struct fallback_to_none
Chris@16: {
Chris@16:     enum { guaranteed_result = false };
Chris@16: 
Chris@16:     /*!
Chris@16:      * The method is called in order to apply a function object to the default value.
Chris@16:      */
Chris@16:     template< typename FunT >
Chris@16:     static bool apply_default(FunT&)
Chris@16:     {
Chris@16:         return false;
Chris@16:     }
Chris@16: 
Chris@16:     /*!
Chris@16:      * The method is called in order to apply a function object to the default value.
Chris@16:      */
Chris@16:     template< typename FunT >
Chris@16:     static bool apply_default(FunT const&)
Chris@16:     {
Chris@16:         return false;
Chris@16:     }
Chris@16: 
Chris@16:     /*!
Chris@16:      * The method is called when value extraction failed because the attribute value has different type than requested.
Chris@16:      */
Chris@16:     static void on_invalid_type(type_info_wrapper const&)
Chris@16:     {
Chris@16:     }
Chris@16: 
Chris@16:     /*!
Chris@16:      * The method is called when value extraction failed because the attribute value was not found.
Chris@16:      */
Chris@16:     static void on_missing_value()
Chris@16:     {
Chris@16:     }
Chris@16: };
Chris@16: 
Chris@16: /*!
Chris@16:  * The \c fallback_to_throw policy results in throwing an exception if the attribute value cannot be extracted.
Chris@16:  */
Chris@16: struct fallback_to_throw
Chris@16: {
Chris@16:     enum { guaranteed_result = true };
Chris@16: 
Chris@16:     /*!
Chris@16:      * The method is called in order to apply a function object to the default value.
Chris@16:      */
Chris@16:     template< typename FunT >
Chris@16:     static bool apply_default(FunT&)
Chris@16:     {
Chris@16:         return false;
Chris@16:     }
Chris@16: 
Chris@16:     /*!
Chris@16:      * The method is called in order to apply a function object to the default value.
Chris@16:      */
Chris@16:     template< typename FunT >
Chris@16:     static bool apply_default(FunT const&)
Chris@16:     {
Chris@16:         return false;
Chris@16:     }
Chris@16: 
Chris@16:     /*!
Chris@16:      * The method is called when value extraction failed because the attribute value has different type than requested.
Chris@16:      */
Chris@16:     static void on_invalid_type(type_info_wrapper const& t)
Chris@16:     {
Chris@16:         BOOST_LOG_THROW_DESCR_PARAMS(invalid_type, "Attribute value has incompatible type", (t));
Chris@16:     }
Chris@16: 
Chris@16:     /*!
Chris@16:      * The method is called when value extraction failed because the attribute value was not found.
Chris@16:      */
Chris@16:     static void on_missing_value()
Chris@16:     {
Chris@16:         BOOST_LOG_THROW_DESCR(missing_value, "Attribute value not found");
Chris@16:     }
Chris@16: };
Chris@16: 
Chris@16: /*!
Chris@16:  * The \c fallback_to_default policy results in a default value if the attribute value cannot be extracted.
Chris@16:  */
Chris@16: template< typename DefaultT >
Chris@16: struct fallback_to_default
Chris@16: {
Chris@16:     enum { guaranteed_result = true };
Chris@16: 
Chris@16:     //! Default value type
Chris@16:     typedef typename remove_cv< typename remove_reference< DefaultT >::type >::type default_type;
Chris@16: 
Chris@16:     /*!
Chris@16:      * Default constructor.
Chris@16:      */
Chris@16:     fallback_to_default() : m_default()
Chris@16:     {
Chris@16:     }
Chris@16: 
Chris@16:     /*!
Chris@16:      * Initializing constructor.
Chris@16:      */
Chris@16:     explicit fallback_to_default(default_type const& def_val) : m_default(def_val)
Chris@16:     {
Chris@16:     }
Chris@16: 
Chris@16:     /*!
Chris@16:      * The method is called in order to apply a function object to the default value.
Chris@16:      */
Chris@16:     template< typename FunT >
Chris@16:     bool apply_default(FunT& fun) const
Chris@16:     {
Chris@16:         fun(m_default);
Chris@16:         return true;
Chris@16:     }
Chris@16: 
Chris@16:     /*!
Chris@16:      * The method is called in order to apply a function object to the default value.
Chris@16:      */
Chris@16:     template< typename FunT >
Chris@16:     bool apply_default(FunT const& fun) const
Chris@16:     {
Chris@16:         fun(m_default);
Chris@16:         return true;
Chris@16:     }
Chris@16: 
Chris@16:     /*!
Chris@16:      * The method is called when value extraction failed because the attribute value has different type than requested.
Chris@16:      */
Chris@16:     static void on_invalid_type(type_info_wrapper const&)
Chris@16:     {
Chris@16:     }
Chris@16: 
Chris@16:     /*!
Chris@16:      * The method is called when value extraction failed because the attribute value was not found.
Chris@16:      */
Chris@16:     static void on_missing_value()
Chris@16:     {
Chris@16:     }
Chris@16: 
Chris@16: private:
Chris@16:     //! Default value
Chris@16:     DefaultT m_default;
Chris@16: };
Chris@16: 
Chris@16: BOOST_LOG_CLOSE_NAMESPACE // namespace log
Chris@16: 
Chris@16: } // namespace boost
Chris@16: 
Chris@16: #include <boost/log/detail/footer.hpp>
Chris@16: 
Chris@16: #endif // BOOST_LOG_ATTRIBUTES_FALLBACK_POLICY_HPP_INCLUDED_