ceph/src/boost/boost/log/attributes/constant.hpp

   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   constant.hpp
   9  * \author Andrey Semashev
  10  * \date   15.04.2007
  11  *
  12  * The header contains implementation of a constant attribute.
  13  */
  14
  15 #ifndef BOOST_LOG_ATTRIBUTES_CONSTANT_HPP_INCLUDED_
  16 #define BOOST_LOG_ATTRIBUTES_CONSTANT_HPP_INCLUDED_
  17
  18 #include <boost/move/core.hpp>
  19 #include <boost/move/utility_core.hpp>
  20 #include <boost/type_traits/remove_reference.hpp>
  21 #include <boost/type_traits/is_nothrow_move_constructible.hpp>
  22 #include <boost/log/detail/config.hpp>
  23 #include <boost/log/detail/embedded_string_type.hpp>
  24 #include <boost/log/attributes/attribute.hpp>
  25 #include <boost/log/attributes/attribute_cast.hpp>
  26 #include <boost/log/attributes/attribute_value_impl.hpp>
  27 #include <boost/log/detail/header.hpp>
  28
  29 #ifdef BOOST_HAS_PRAGMA_ONCE
  30 #pragma once
  31 #endif
  32
  33 namespace boost {
  34
  35 BOOST_LOG_OPEN_NAMESPACE
  36
  37 namespace attributes {
  38
  39 /*!
  40  * \brief A class of an attribute that holds a single constant value
  41  *
  42  * The constant is a simplest and one of the most frequently used types of attributes.
  43  * It stores a constant value, which it eventually returns as its value each time
  44  * requested.
  45  */
  46 template< typename T >
  47 class constant :
  48     public attribute
  49 {
  50 public:
  51     //! Attribute value type
  52     typedef T value_type;
  53
  54 protected:
  55     //! Factory implementation
  56     class BOOST_SYMBOL_VISIBLE impl :
  57         public attribute_value_impl< value_type >
  58     {
  59         //! Base type
  60         typedef attribute_value_impl< value_type > base_type;
  61
  62     public:
  63         /*!
  64          * Constructor with the stored value initialization
  65          */
  66         explicit impl(value_type const& value) : base_type(value) {}
  67         /*!
  68          * Constructor with the stored value initialization
  69          */
  70         explicit impl(BOOST_RV_REF(value_type) value) BOOST_NOEXCEPT_IF(boost::is_nothrow_move_constructible< value_type >::value) :
  71             base_type(boost::move(value))
  72         {
  73         }
  74     };
  75
  76 public:
  77     /*!
  78      * Constructor with the stored value initialization
  79      */
  80     explicit constant(value_type const& value) : attribute(new impl(value)) {}
  81     /*!
  82      * Constructor with the stored value initialization
  83      */
  84     explicit constant(BOOST_RV_REF(value_type) value) : attribute(new impl(boost::move(value))) {}
  85     /*!
  86      * Constructor for casting support
  87      */
  88     explicit constant(cast_source const& source) : attribute(source.as< impl >())
  89     {
  90     }
  91
  92     /*!
  93      * \return Reference to the contained value.
  94      */
  95     value_type const& get() const
  96     {
  97         return static_cast< impl* >(this->get_impl())->get();
  98     }
  99 };
 100
 101 /*!
 102  * The function constructs a \c constant attribute containing the provided value.
 103  * The function automatically converts C string arguments to \c std::basic_string objects.
 104  */
 105 template< typename T >
 106 inline constant<
 107     typename boost::log::aux::make_embedded_string_type<
 108         typename remove_reference< T >::type
 109     >::type
 110 > make_constant(BOOST_FWD_REF(T) val)
 111 {
 112     typedef typename boost::log::aux::make_embedded_string_type<
 113         typename remove_reference< T >::type
 114     >::type value_type;
 115     return constant< value_type >(boost::forward< T >(val));
 116 }
 117
 118 } // namespace attributes
 119
 120 BOOST_LOG_CLOSE_NAMESPACE // namespace log
 121
 122 } // namespace boost
 123
 124 #include <boost/log/detail/footer.hpp>
 125
 126 #endif // BOOST_LOG_ATTRIBUTES_CONSTANT_HPP_INCLUDED_