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value_init.hpp now no longer distinguished between workaround and non-workaround, because many compilers don't do value-initialization well. Fixed copy construction and assignment -- discussed with Fernando Cacciola

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[SVN r41942]
This commit is contained in:
Niels Dekker 2007-12-09 22:49:58 +00:00
parent 8080673977
commit 01274cf6ac
1 changed files with 63 additions and 60 deletions
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123
include/boost/utility/value_init.hpp
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@ -7,103 +7,106 @@
// 21 Ago 2002 (Created) Fernando Cacciola
// 07 Set 2007 (Worked around MSVC++ bug) Fernando Cacciola, Niels Dekker
// 16 Nov 2007 (Refactoring: removed private base classes) Fernando Cacciola, Niels Dekker
// 09 Dec 2007 (Worked around various compiler bugs) Fernando Cacciola, Niels Dekker
//
#ifndef BOOST_UTILITY_VALUE_INIT_21AGO2002_HPP
#define BOOST_UTILITY_VALUE_INIT_21AGO2002_HPP
#include <boost/detail/select_type.hpp>
#include <boost/type_traits/cv_traits.hpp>
#include <boost/detail/workaround.hpp>
// Microsoft Visual C++ does not correctly support value initialization, as reported by
// Pavel Kuznetsov (MetaCommunications Engineering), 7/28/2005, Feedback ID 100744,
// Feedback Title: Value-initialization in new-expression
// 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
// The report was closed at 11/14/2006, and its status was set to "Closed (Won't Fix)".
// Luckily, even in the presence of this compiler bug, boost::value_initialized will still
// do its job correctly, when using the following workaround:
#if BOOST_WORKAROUND(BOOST_MSVC, BOOST_TESTED_AT(1500))
# define BOOST_UTILITY_VALUE_INIT_WORKAROUND
#endif
#ifdef BOOST_UTILITY_VALUE_INIT_WORKAROUND
// 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.
#include <boost/aligned_storage.hpp>
#include <boost/detail/select_type.hpp>
#include <boost/detail/workaround.hpp>
#include <boost/type_traits/cv_traits.hpp>
#include <boost/type_traits/alignment_of.hpp>
#include <cstring>
#include <new>
#ifdef BOOST_MSVC
#pragma warning(push)
#if _MSC_VER >= 1310
// When using MSVC 7.1 or higher, placement new, "new (&x) T()", 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.
#pragma warning(disable: 4345)
#endif
#endif
namespace boost {
template<class T>
class value_initialized
{
private :
mutable typename ::boost::aligned_storage<sizeof(T), ::boost::alignment_of<T>::value>::type x;
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
::boost::aligned_storage<sizeof(wrapper), ::boost::alignment_of<wrapper>::value>::type x;
public :
value_initialized()
{
std::memset(&x, 0, sizeof(x));
new (&x) T();
#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.
#pragma warning(disable: 4345)
#endif
#endif
new (&x) wrapper();
#ifdef BOOST_MSVC
#pragma warning(pop)
#endif
}
value_initialized(value_initialized const & arg)
{
void const * const ptr = &(arg.x);
new (&x) wrapper( *static_cast<wrapper const *>(ptr) );
}
value_initialized & operator=(value_initialized const & arg)
{
T & this_data = this->data();
T const & arg_data = arg.data();
this_data = arg_data;
return *this;
}
~value_initialized()
{
void * ptr = &x;
static_cast<T*>(ptr)->T::~T();
void * const ptr = &x;
static_cast<wrapper *>(ptr)->wrapper::~wrapper();
}
T& data() const
{
void * ptr = &x;
return *static_cast<T*>(ptr);
void * const ptr = &x;
return static_cast<wrapper *>(ptr)->data;
}
operator T&() const { return this->data(); }
} ;
#ifdef BOOST_MSVC
// Restores the state of warning C4345.
#pragma warning(pop)
#endif
#else
namespace boost {
template<class T>
class value_initialized
{
public :
value_initialized() : x() {}
T& data() const { return x; }
operator T&() const { return this->data(); }
mutable
#if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
typename
#endif
::boost::remove_const<T>::type x ;
} ;
#endif
template<class T>