Re: C bug of the day

[kanze@gabi-soft.fr]

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tmoran@acm.org wrote in message
news:<N3mIa.721016$Si4.853728@rwcrnsc51.ops.asp.att.net>...
> > classical idiom in C++ is to copy construct a temporary from the
> > right hand side (the anonymous object which is created), then swap
> > all of the fields with the target object, so that the anonymous
> > object has the bit pattern of the original object, and vice versa.
> > On leaving the > >...

> >Because of the swap, C++ gets by with one finalization less:-).  On the

>   What if the object is on a linked list with back pointers so that
> after the swap the pointers are wrong? Or if it just contains pointers
> to internal parts of itself?

It's up to the programmer to make the swap work correctly.  Most of the
time, it isn't a problem -- nobody should have any pointers to the
temporary object in function, for example.  As for the linked list
example, I would imagine that the swap function shouldn't touch the
pointers involved.  The target object remains linked where it was,
regardless of the assignment.

Obviously, this idiom doesn't work well with objects that, for example,
register themselves somewhere (i.e. the constructor "publishes" the
objects addess).  But if my experience is typical, such objects have
identity, and shouldn't be assigned or copied anyway.  About a third of
my C++ classes don't allow assignment at all, for such reasons.

--
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