[boost] Re: copy_on_write

From: Alexander Terekhov (terekhov_at_[hidden])
Date: 2005-06-01 14:03:46

Peter Dimov wrote:
> 
> Alexander Terekhov wrote:
> 
> > Yeah, simply put, mutations of std::string object may invalidate
> > references and iterators (with COW inspired semantics for non-
> > const operator[]() et al. )... threads or no threads, COW or no
> > COW.
> 
> Umm, not exactly.
> 
> int x = s[0];
> 
> (with non-const s) does not invalidate if COW isn't used, 

Uhmm, that's not what the standard says.

Well, apart from

http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#263
http://groups-beta.google.com/group/comp.lang.c++.moderated/msg/1fc8476dbadf7bff

I suggest you simply read between the lines of "These rules are 
formulated to allow, but not require, a reference counted 
implemenation. A reference counted implementation must have the 
same semantics as a non-reference counted implementation" note
having efficient COW implementation in your mind. (Among other
things I mean invalidation on refcount > 1 with refcount == 0 
representing unshareable state.)

;-)

regards,
alexander.