[Development] Move ctors for q_declare_shared types

[Olivier Goffart]

On Friday 26. June 2015 15:42:31 Daniel Teske wrote:
> > > For standard containers, this is specified in *container.requirements*
> > > To quote, with: a being a container and rv a non-const rvalue of the
> > > same
> > > type:
> > > 
> > > a = rv
> > > 
> > > "All existing elements of a are either move assigned to or destroyed,"
> > > 
> > > I do not see any reason why our containers should not give the same
> > > guarantee for move assignment and consider this a bug.
> > 
> > Is this really that much different?
> 
> There's a huge difference between "either move assigned to or destroyed" and
> not doing that.
> 
> I'm not sure where you are disagreeing, so can you point out to which of
> those 4 statements you don't agree?
> 
> - Standard containers guarantee that the old elements get either move
> assigned or destroyed.

I partially disagree.
The wording seems to indeed implies that the move assignement operator of 
std::vector should do iterate over all elements to destroy or move them. But 
in practice, GCC implementation does not do that:
http://cpp.sh/2s4w

Is it a bug in the GCC's stdlib implemenation?  Or is it a misunderstanding of 
the wording of the standard?

> - QVector does not give the same guarantee, because it uses swap.

Irrelevant.
 
> - QVector should give the same guarantee as the standard containers.

I disagree with that. QVector is not std::vector. At first, it is implicitly 
shared, so that's already a big difference. And therefore we can allow 
ourselfs many more differences.

-- 
Olivier 

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