On Wed, 2008-04-09 at 17:07 +0300, Peter Dimov wrote:
Daniel Frey wrote:
is done the the ctor body. There is even a comment which suggests that there is a problem with doing it before pn, it would not be "safe". What exactly does this mean? px is just a plain pointer, so AFAICS it
No, copying a deleted pointer is undefined behavior.
Ah, thanks. I just learned something new. :)
2) in detail/shared_count.hpp, operator= for shared_count has an optimization for tmp==pi_. At least I think that it's just an optimization and it would work without the check. OTOH, operator= for weak_count does not check for tmp==pi_. Why? Is there any deeper reason that these two code fragements differ?
It's a performance optimization. There's no deep reason for the difference.
Maybe it's worth to do the same optimization in weak_ptr::operator= then?
3) I asked about this point before, but got no real answer: There is no throw specification in shared_from_this()'s documentation. AFAICS, shared_from_this() (if used correctly) can not throw. But will this be guaranteed?
I'm not sure. It's not guaranteed by TR1 or the draft standard, and I haven't considered the issue in detail to be confident that this is a defect.
I have use cases which would be a lot easier to implement if shared_from_this() never throws. And - at least with the "old" implementation - I don't see any reason why this guarantee should not hold. Of course it's not a defect, but to me it seems desirable. Since you are also currently working on enable_shared_from_this (which increases the overhead): Would it make sense if I develop a patch based on the old version which tries to use detail::weak_count instead of weak_ptr to create an even lighter, classic enable_shared_from_this? At least to me the overhead of deriving from enable_shared_from_this is important... Regards, Daniel