Re: [webkit-dev] deleteOwnedPtr(T* ptr)

2010-11-11 Thread Finnur Thorarinsson 
Umm... shouldn't this behavior be commented so that people are not left
wondering why it fails and trying to fix it?

On Wed, Nov 10, 2010 at 16:04, Darin Adler da...@apple.com wrote:

 On Nov 10, 2010, at 2:33 PM, Daebarkee Jung wrote:

  I found that the following lines made errors:
  // OwnPtrCommon.h
  template typename T inline void deleteOwnedPtr(T* ptr)
  {
  typedef char known[sizeof(T) ? 1 : -1];
  if (sizeof(known))
delete ptr;
  }
 
  I am very curious about why the author wrote like the above.
  What could be the author's intention?

 The code is to prevent issues like the ones described on these websites:

 http://stackoverflow.com/questions/1767679/incomplete-type-memory-leaks

 http://bytes.com/topic/c/answers/611877-gcc-class-forward-declarations-destructor-calls

 http://connect.microsoft.com/VisualStudio/feedback/details/231177/delete-of-pointer-to-incomplete-class

 If we delete a pointer and the object has incomplete type, we get undefined
 behavior. Instead this code causes compilation to fail if the object has
 incomplete type. The use of a negative number for the size of an array is a
 way to guarantee we get a compilation error.

 Your alternate version might also work; I’m not sure.

-- Darin

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Re: [webkit-dev] deleteOwnedPtr(T* ptr)

2010-11-11 Thread Daebarkee Jung 
Thanks, all of you.
Now, everything is clear.

Daebark

On Thu, Nov 11, 2010 at 2:24 AM, Finnur Thorarinsson fin...@chromium.orgwrote:

 Umm... shouldn't this behavior be commented so that people are not left
 wondering why it fails and trying to fix it?

 On Wed, Nov 10, 2010 at 16:04, Darin Adler da...@apple.com wrote:

 On Nov 10, 2010, at 2:33 PM, Daebarkee Jung wrote:

  I found that the following lines made errors:
  // OwnPtrCommon.h
  template typename T inline void deleteOwnedPtr(T* ptr)
  {
  typedef char known[sizeof(T) ? 1 : -1];
  if (sizeof(known))
delete ptr;
  }
 
  I am very curious about why the author wrote like the above.
  What could be the author's intention?

 The code is to prevent issues like the ones described on these websites:

 http://stackoverflow.com/questions/1767679/incomplete-type-memory-leaks

 http://bytes.com/topic/c/answers/611877-gcc-class-forward-declarations-destructor-calls

 http://connect.microsoft.com/VisualStudio/feedback/details/231177/delete-of-pointer-to-incomplete-class

 If we delete a pointer and the object has incomplete type, we get
 undefined behavior. Instead this code causes compilation to fail if the
 object has incomplete type. The use of a negative number for the size of an
 array is a way to guarantee we get a compilation error.

 Your alternate version might also work; I’m not sure.

-- Darin

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 webkit-dev@lists.webkit.org
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Re: [webkit-dev] deleteOwnedPtr(T* ptr)

2010-11-11 Thread Darin Adler 
On Nov 11, 2010, at 12:24 AM, Finnur Thorarinsson wrote:

 Umm... shouldn't this behavior be commented so that people are not left 
 wondering why it fails and trying to fix it?

Sure, sounds good.

Instructions for submitting patches to add things like those comments are at 
http://webkit.org/coding/contributing.html.

-- Darin

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Re: [webkit-dev] deleteOwnedPtr(T* ptr)

2010-11-11 Thread David Levin 
Do or do not. Then, there is no question. :)

btw, in another code base, you may familiar with, the comment is the
variable name:
http://www.google.com/codesearch?q=type_must_be_completeexact_package=chromium

On Thu, Nov 11, 2010 at 12:24 AM, Finnur Thorarinsson
fin...@chromium.orgwrote:

 Umm... shouldn't this behavior be commented so that people are not left
 wondering why it fails and trying to fix it?


 On Wed, Nov 10, 2010 at 16:04, Darin Adler da...@apple.com wrote:

 On Nov 10, 2010, at 2:33 PM, Daebarkee Jung wrote:

  I found that the following lines made errors:
  // OwnPtrCommon.h
  template typename T inline void deleteOwnedPtr(T* ptr)
  {
  typedef char known[sizeof(T) ? 1 : -1];
  if (sizeof(known))
delete ptr;
  }
 
  I am very curious about why the author wrote like the above.
  What could be the author's intention?

 The code is to prevent issues like the ones described on these websites:

 http://stackoverflow.com/questions/1767679/incomplete-type-memory-leaks

 http://bytes.com/topic/c/answers/611877-gcc-class-forward-declarations-destructor-calls

 http://connect.microsoft.com/VisualStudio/feedback/details/231177/delete-of-pointer-to-incomplete-class

 If we delete a pointer and the object has incomplete type, we get
 undefined behavior. Instead this code causes compilation to fail if the
 object has incomplete type. The use of a negative number for the size of an
 array is a way to guarantee we get a compilation error.

 Your alternate version might also work; I’m not sure.

-- Darin

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 webkit-dev@lists.webkit.org
 http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev



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Re: [webkit-dev] deleteOwnedPtr(T* ptr)

2010-11-11 Thread Maciej Stachowiak 

On Nov 11, 2010, at 7:20 AM, Darin Adler wrote:

 On Nov 11, 2010, at 12:24 AM, Finnur Thorarinsson wrote:
 
 Umm... shouldn't this behavior be commented so that people are not left 
 wondering why it fails and trying to fix it?
 
 Sure, sounds good.
 
 Instructions for submitting patches to add things like those comments are at 
 http://webkit.org/coding/contributing.html.

Even better than a comment would be to use the COMPILE_ASSERT macro.

Regards,
Maciej

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[webkit-dev] deleteOwnedPtr(T* ptr)

2010-11-10 Thread Daebarkee Jung 
Hi,

I found that the following lines made errors:
// OwnPtrCommon.h
template typename T inline void deleteOwnedPtr(T* ptr)
{
typedef char known[sizeof(T) ? 1 : -1];
if (sizeof(known))
delete ptr;
}

I am very curious about why the author wrote like the above.
What could be the author's intention?

For error-fix, I changed it like the following:

template typename T inline void deleteOwnedPtr(T* ptr)
{
  if(sizeof(T)0)
delete ptr;
}

What could be the above code's mistake?


Thanks,

Daebark
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Re: [webkit-dev] deleteOwnedPtr(T* ptr)

2010-11-10 Thread Darin Adler 
On Nov 10, 2010, at 2:33 PM, Daebarkee Jung wrote:

 I found that the following lines made errors:
 // OwnPtrCommon.h
 template typename T inline void deleteOwnedPtr(T* ptr)
 {
 typedef char known[sizeof(T) ? 1 : -1];
 if (sizeof(known))
   delete ptr;
 }
 
 I am very curious about why the author wrote like the above.
 What could be the author's intention?

The code is to prevent issues like the ones described on these websites:

http://stackoverflow.com/questions/1767679/incomplete-type-memory-leaks
http://bytes.com/topic/c/answers/611877-gcc-class-forward-declarations-destructor-calls
http://connect.microsoft.com/VisualStudio/feedback/details/231177/delete-of-pointer-to-incomplete-class

If we delete a pointer and the object has incomplete type, we get undefined 
behavior. Instead this code causes compilation to fail if the object has 
incomplete type. The use of a negative number for the size of an array is a way 
to guarantee we get a compilation error.

Your alternate version might also work; I’m not sure.

-- Darin

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