63e88f80
 Hu Chunming
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/*
* Copyright Andrey Semashev 2007 - 2015.
* Distributed under the Boost Software License, Version 1.0.
* (See accompanying file LICENSE_1_0.txt or copy at
* http://www.boost.org/LICENSE_1_0.txt)
*/
/*!
* \file constant.hpp
* \author Andrey Semashev
* \date 15.04.2007
*
* The header contains implementation of a constant attribute.
*/
#ifndef BOOST_LOG_ATTRIBUTES_CONSTANT_HPP_INCLUDED_
#define BOOST_LOG_ATTRIBUTES_CONSTANT_HPP_INCLUDED_
#include <boost/move/core.hpp>
#include <boost/move/utility_core.hpp>
#include <boost/type_traits/remove_reference.hpp>
#include <boost/type_traits/is_nothrow_move_constructible.hpp>
#include <boost/log/detail/config.hpp>
#include <boost/log/detail/embedded_string_type.hpp>
#include <boost/log/attributes/attribute.hpp>
#include <boost/log/attributes/attribute_cast.hpp>
#include <boost/log/attributes/attribute_value_impl.hpp>
#include <boost/log/detail/header.hpp>
#ifdef BOOST_HAS_PRAGMA_ONCE
#pragma once
#endif
namespace boost {
BOOST_LOG_OPEN_NAMESPACE
namespace attributes {
/*!
* \brief A class of an attribute that holds a single constant value
*
* The constant is a simplest and one of the most frequently used types of attributes.
* It stores a constant value, which it eventually returns as its value each time
* requested.
*/
template< typename T >
class constant :
public attribute
{
public:
//! Attribute value type
typedef T value_type;
protected:
//! Factory implementation
class BOOST_SYMBOL_VISIBLE impl :
public attribute_value_impl< value_type >
{
//! Base type
typedef attribute_value_impl< value_type > base_type;
public:
/*!
* Constructor with the stored value initialization
*/
explicit impl(value_type const& value) : base_type(value) {}
/*!
* Constructor with the stored value initialization
*/
explicit impl(BOOST_RV_REF(value_type) value) BOOST_NOEXCEPT_IF(boost::is_nothrow_move_constructible< value_type >::value) :
base_type(boost::move(value))
{
}
};
public:
/*!
* Constructor with the stored value initialization
*/
explicit constant(value_type const& value) : attribute(new impl(value)) {}
/*!
* Constructor with the stored value initialization
*/
explicit constant(BOOST_RV_REF(value_type) value) : attribute(new impl(boost::move(value))) {}
/*!
* Constructor for casting support
*/
explicit constant(cast_source const& source) : attribute(source.as< impl >())
{
}
/*!
* \return Reference to the contained value.
*/
value_type const& get() const
{
return static_cast< impl* >(this->get_impl())->get();
}
};
/*!
* The function constructs a \c constant attribute containing the provided value.
* The function automatically converts C string arguments to \c std::basic_string objects.
*/
template< typename T >
inline constant<
typename boost::log::aux::make_embedded_string_type<
typename remove_reference< T >::type
>::type
> make_constant(BOOST_FWD_REF(T) val)
{
typedef typename boost::log::aux::make_embedded_string_type<
typename remove_reference< T >::type
>::type value_type;
return constant< value_type >(boost::forward< T >(val));
}
} // namespace attributes
BOOST_LOG_CLOSE_NAMESPACE // namespace log
} // namespace boost
#include <boost/log/detail/footer.hpp>
#endif // BOOST_LOG_ATTRIBUTES_CONSTANT_HPP_INCLUDED_
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