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Merged value_init.hpp from trunk, including new boost::initialized_value object. (Was discussed beforehand with Fernando Cacciola.)

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[SVN r46464]
This commit is contained in:
Niels Dekker
2008-06-17 22:14:09 +00:00
parent 50bc75a802
commit 8849fbc52d
1 changed files with 40 additions and 26 deletions
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66
include/boost/utility/value_init.hpp
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@ -1,4 +1,4 @@
// (C) Copyright 2002-2007, Fernando Luis Cacciola Carballal.
// (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
@ -6,29 +6,20 @@
//
// 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
//
#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:
// Microsoft Feedback ID 100744 - Value-initialization in new-expression
// Reported by Pavel Kuznetsov (MetaCommunications Engineering), 2005-07-28
// https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=100744
// GCC Bug 30111 - Value-initialization of POD base class doesn't initialize members
// Reported by Jonathan Wakely, 2006-12-07
// http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30111
// GCC Bug 33916 - Default constructor fails to initialize array members
// Reported by Michael Elizabeth Chastain, 2007-10-26
// http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33916
// Borland Report 51854 - Value-initialization: POD struct should be zero-initialized
// Reported by Niels Dekker (LKEB, Leiden University Medical Center), 2007-11-09
// http://qc.codegear.com/wc/qcmain.aspx?d=51854
// The constructor of boost::value_initialized<T> works around these issues, by
// clearing the bytes of T, before constructing the T object it contains.
// 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 <cstring>
@ -48,23 +39,32 @@ class value_initialized
remove_const<T>::type data;
};
mutable aligned_storage<sizeof(wrapper), alignment_of<wrapper>::value> x;
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.address(), 0, sizeof(x));
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". There is no need to worry about this, though.
// will be default-initialized". It is safe to ignore this warning when using value_initialized.
#pragma warning(disable: 4345)
#endif
#endif
new (x.address()) wrapper();
new (wrapper_address()) wrapper();
#ifdef BOOST_MSVC
#pragma warning(pop)
#endif
@ -72,25 +72,25 @@ class value_initialized
value_initialized(value_initialized const & arg)
{
new (x.address()) wrapper( *static_cast<wrapper const *>(arg.x.address()) );
new (wrapper_address()) wrapper( static_cast<wrapper const &>(*(arg.wrapper_address())));
}
value_initialized & operator=(value_initialized const & arg)
{
T & this_data = this->data();
T const & arg_data = arg.data();
this_data = arg_data;
// 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()
{
static_cast<wrapper *>(x.address())->wrapper::~wrapper();
wrapper_address()->wrapper::~wrapper();
}
T& data() const
{
return static_cast<wrapper *>(x.address())->data;
return wrapper_address()->data;
}
operator T&() const { return this->data(); }
@ -110,6 +110,20 @@ T& get ( value_initialized<T>& x )
return x.data() ;
}
class initialized_value_t
{
public :
template <class T> operator T() const
{
return get( value_initialized<T>() );
}
};
initialized_value_t const initialized_value = {} ;
} // namespace boost