1 /*
2  *          Copyright Andrey Semashev 2007 - 2015.
3  * Distributed under the Boost Software License, Version 1.0.
4  *    (See accompanying file LICENSE_1_0.txt or copy at
5  *          http://www.boost.org/LICENSE_1_0.txt)
6  */
7 /*!
8  * \file   fallback_policy_fwd.hpp
9  * \author Andrey Semashev
10  * \date   18.08.2012
11  *
12  * The header contains forward declaration of fallback policies when attribute value visitation or extraction fails.
13  */
14 
15 #ifndef BOOST_LOG_ATTRIBUTES_FALLBACK_POLICY_FWD_HPP_INCLUDED_
16 #define BOOST_LOG_ATTRIBUTES_FALLBACK_POLICY_FWD_HPP_INCLUDED_
17 
18 #include <boost/log/detail/config.hpp>
19 
20 #ifdef BOOST_HAS_PRAGMA_ONCE
21 #pragma once
22 #endif
23 
24 namespace boost {
25 
26 BOOST_LOG_OPEN_NAMESPACE
27 
28 /*!
29  * The \c fallback_to_none policy results in returning an empty value reference if the attribute value cannot be extracted.
30  */
31 struct fallback_to_none;
32 
33 /*!
34  * The \c fallback_to_throw policy results in throwing an exception if the attribute value cannot be extracted.
35  */
36 struct fallback_to_throw;
37 
38 /*!
39  * The \c fallback_to_default policy results in a default value if the attribute value cannot be extracted.
40  */
41 template< typename DefaultT >
42 struct fallback_to_default;
43 
44 BOOST_LOG_CLOSE_NAMESPACE // namespace log
45 
46 } // namespace boost
47 
48 #endif // BOOST_LOG_ATTRIBUTES_FALLBACK_POLICY_FWD_HPP_INCLUDED_
49