log/attributes/fallback_policy_fwd.hpp

0001 /*
0002  *          Copyright Andrey Semashev 2007 - 2015.
0003  * Distributed under the Boost Software License, Version 1.0.
0004  *    (See accompanying file LICENSE_1_0.txt or copy at
0005  *          http://www.boost.org/LICENSE_1_0.txt)
0006  */
0007 /*!
0008  * \file   fallback_policy_fwd.hpp
0009  * \author Andrey Semashev
0010  * \date   18.08.2012
0011  *
0012  * The header contains forward declaration of fallback policies when attribute value visitation or extraction fails.
0013  */
0014
0015 #ifndef BOOST_LOG_ATTRIBUTES_FALLBACK_POLICY_FWD_HPP_INCLUDED_
0016 #define BOOST_LOG_ATTRIBUTES_FALLBACK_POLICY_FWD_HPP_INCLUDED_
0017
0018 #include <boost/log/detail/config.hpp>
0019
0020 #ifdef BOOST_HAS_PRAGMA_ONCE
0021 #pragma once
0022 #endif
0023
0024 namespace boost {
0025
0026 BOOST_LOG_OPEN_NAMESPACE
0027
0028 /*!
0029  * The \c fallback_to_none policy results in returning an empty value reference if the attribute value cannot be extracted.
0030  */
0031 struct fallback_to_none;
0032
0033 /*!
0034  * The \c fallback_to_throw policy results in throwing an exception if the attribute value cannot be extracted.
0035  */
0036 struct fallback_to_throw;
0037
0038 /*!
0039  * The \c fallback_to_default policy results in a default value if the attribute value cannot be extracted.
0040  */
0041 template< typename DefaultT >
0042 struct fallback_to_default;
0043
0044 BOOST_LOG_CLOSE_NAMESPACE // namespace log
0045
0046 } // namespace boost
0047
0048 #endif // BOOST_LOG_ATTRIBUTES_FALLBACK_POLICY_FWD_HPP_INCLUDED_