154 lines
3.7 KiB
C++
154 lines
3.7 KiB
C++
// (C) Copyright 2002-2008, Fernando Luis Cacciola Carballal.
|
|
//
|
|
// 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)
|
|
//
|
|
// 21 Ago 2002 (Created) Fernando Cacciola
|
|
// 24 Dec 2007 (Refactored and worked around various compiler bugs) Fernando Cacciola, Niels Dekker
|
|
// 23 May 2008 (Fixed operator= const issue, added initialized_value) Niels Dekker, Fernando Cacciola
|
|
// 21 Ago 2008 (Added swap) Niels Dekker, Fernando Cacciola
|
|
// 20 Feb 2009 (Fixed logical const-ness issues) Niels Dekker, Fernando Cacciola
|
|
//
|
|
#ifndef BOOST_UTILITY_VALUE_INIT_21AGO2002_HPP
|
|
#define BOOST_UTILITY_VALUE_INIT_21AGO2002_HPP
|
|
|
|
// Note: The implementation of boost::value_initialized had to deal with the
|
|
// fact that various compilers haven't fully implemented value-initialization.
|
|
// The constructor of boost::value_initialized<T> works around these compiler
|
|
// issues, by clearing the bytes of T, before constructing the T object it
|
|
// contains. More details on these issues are at libs/utility/value_init.htm
|
|
|
|
#include <boost/aligned_storage.hpp>
|
|
#include <boost/detail/workaround.hpp>
|
|
#include <boost/static_assert.hpp>
|
|
#include <boost/type_traits/cv_traits.hpp>
|
|
#include <boost/type_traits/alignment_of.hpp>
|
|
#include <boost/swap.hpp>
|
|
#include <cstring>
|
|
#include <new>
|
|
|
|
namespace boost {
|
|
|
|
template<class T>
|
|
class value_initialized
|
|
{
|
|
private :
|
|
struct wrapper
|
|
{
|
|
#if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x592))
|
|
typename
|
|
#endif
|
|
remove_const<T>::type data;
|
|
};
|
|
|
|
mutable
|
|
#if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x592))
|
|
typename
|
|
#endif
|
|
aligned_storage<sizeof(wrapper), alignment_of<wrapper>::value>::type x;
|
|
|
|
wrapper * wrapper_address() const
|
|
{
|
|
return static_cast<wrapper *>( static_cast<void*>(&x));
|
|
}
|
|
|
|
public :
|
|
|
|
value_initialized()
|
|
{
|
|
std::memset(&x, 0, sizeof(x));
|
|
#ifdef BOOST_MSVC
|
|
#pragma warning(push)
|
|
#if _MSC_VER >= 1310
|
|
// When using MSVC 7.1 or higher, the following placement new expression may trigger warning C4345:
|
|
// "behavior change: an object of POD type constructed with an initializer of the form ()
|
|
// will be default-initialized". It is safe to ignore this warning when using value_initialized.
|
|
#pragma warning(disable: 4345)
|
|
#endif
|
|
#endif
|
|
new (wrapper_address()) wrapper();
|
|
#ifdef BOOST_MSVC
|
|
#pragma warning(pop)
|
|
#endif
|
|
}
|
|
|
|
value_initialized(value_initialized const & arg)
|
|
{
|
|
new (wrapper_address()) wrapper( static_cast<wrapper const &>(*(arg.wrapper_address())));
|
|
}
|
|
|
|
value_initialized & operator=(value_initialized const & arg)
|
|
{
|
|
// Assignment is only allowed when T is non-const.
|
|
BOOST_STATIC_ASSERT( ! is_const<T>::value );
|
|
*wrapper_address() = static_cast<wrapper const &>(*(arg.wrapper_address()));
|
|
return *this;
|
|
}
|
|
|
|
~value_initialized()
|
|
{
|
|
wrapper_address()->wrapper::~wrapper();
|
|
}
|
|
|
|
T const & data() const
|
|
{
|
|
return wrapper_address()->data;
|
|
}
|
|
|
|
T& data()
|
|
{
|
|
return wrapper_address()->data;
|
|
}
|
|
|
|
void swap(value_initialized & arg)
|
|
{
|
|
::boost::swap( this->data(), arg.data() );
|
|
}
|
|
|
|
operator T const &() const { return this->data(); }
|
|
|
|
operator T&() { return this->data(); }
|
|
|
|
} ;
|
|
|
|
|
|
|
|
|
|
|
|
template<class T>
|
|
T const& get ( value_initialized<T> const& x )
|
|
{
|
|
return x.data() ;
|
|
}
|
|
template<class T>
|
|
T& get ( value_initialized<T>& x )
|
|
{
|
|
return x.data() ;
|
|
}
|
|
|
|
template<class T>
|
|
void swap ( value_initialized<T> & lhs, value_initialized<T> & rhs )
|
|
{
|
|
lhs.swap(rhs) ;
|
|
}
|
|
|
|
|
|
class initialized_value_t
|
|
{
|
|
public :
|
|
|
|
template <class T> operator T() const
|
|
{
|
|
return get( value_initialized<T>() );
|
|
}
|
|
};
|
|
|
|
initialized_value_t const initialized_value = {} ;
|
|
|
|
|
|
} // namespace boost
|
|
|
|
|
|
#endif
|