Re: [boost] New Library Proposal: dual_state

From: Calum Grant (calum_at_[hidden])
Date: 2005-07-16 11:40:06

Andrey Melnikov wrote:
> David Abrahams wrote:
> > "Calum Grant" <calum_at_[hidden]> writes:
> >>In the absence of Boost, I would probably use a 
> std::auto_ptr to store 
> >>an optional field, which is, um, a smart pointer.  I realize that 
> >>Optional is implemented slightly differently.
> > 
> > 
> > I wouldn't characterize it as a "slight" difference.
> > 
> I hate extra dynamic memory allocation even more than I hate extra 
> copies, because the former cannot be optimized out and usually takes 
> more time than 10 extra copies. Well, pool allocators help a lot 
> sometimes, but it's an optimization technology.
> 
> I like Boost.Optional because it offers a good way to deal with 
> optonality without any extra pointers, memory allocations, special 
> "NULL" values or construction or copy operations . I think it's way 
> different from the concept of smart pointers.

I completely take your point that Boost.Optional would be drastically
more efficient in many circumstances.  But I would also say it could be
less efficient than dynamic memory allocation in a limited number of
cases.

But we're talking about private implementation.  From a semantic
perspective, Optional behaves like a smart pointer with a "copy on
assign" policy.  Perhaps there would be fewer howls of disapproval if I
called it a smart container, not a smart pointer.

If an implementation improves a smart container/pointer in this
circumstance then that's fanstastic.

Calum