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