On 2010-11-30 13:23, Philippe Cayouette wrote:
If anyone is interested in the code, it can be found at:
http://208.106.110.44/~ansel/boost/enable_shared_from_polymorphic.patch
This patch is against the current SVN version of boost.
The only cast that occurs in this code is a static_cast that downcasts from enable_shared_from_polymorphic<T> to T. I have read the relevant portions of the standard several times and I beleive this is valid, but I would definitely be curious if wiser heads agree with my reading.
I finally took the time to test your latest patch from the URL you provided. I am using VS2005 right now and it does not work, in fact, the function sp_enable_shared_from_this in your file never got called, resulting in an uninitialized internal weak_ptr. It builds successfully and even give the illusion that it works! I will try to explain the problem. The function shared_from_this of the class enable_shared_from_polymorphic recreates a shared_ptr using "this", the weak_ptr you pass to the shared_ptr constructor is NULL and then constructs a shared_ptr with px = this and pn.pi_ = NULL. Now if you copy the shared_from_this into a second shared_ptr while the original shared_ptr is still alive, the copy will work (this is the illusion I was talking about). However, when the original shared_ptr goes out of context, it is destroyed and if you use the copy shared_ptr (still in context), you will work on deleted memory... A good example is worth a million words. I have put a test file over there: http://spoluck.ca:8000/boost/SharedFromThisTest.cpp Debug step in it and you will see. You can set USING_VARIADIC_AND_FACTORY_METHOD to 1 to fall back to my original solution. You will need to have my original support file for that (still at the same URL). http://spoluck.ca:8000/boost/EnableSharedFromThis.h http://spoluck.ca:8000/boost/SmartPtrBuilder.h Did I used your patch erroneously? Regards, Philippe