Re: [boost] New Library Proposal: dual_state

From: David Abrahams (dave_at_[hidden])
Date: 2005-07-15 20:31:59

"Calum Grant" <calum_at_[hidden]> writes:

> I've been following this dual_state vs optional discussion for a while.
> It seems to me that one should really have a policy class that defines
> the default behaviour when the value is unassigned.  This policy should
> define whether to 
>
>   - throw an exception
>   - construct an object on the fly
>   - return a default 
>   - return a null pointer
>   - whether to return by value or by reference
>
> A second point, can't all this be achieved by adding policies to smart
> pointers?

Whoa; smart pointers and boost::optional are not very closely related
beasts.  If you add enough policies to std::list you could probably
handle this use case, too.  I don't think finding something to
policy-ize is always the best way to fit new designs into an existing
framework.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com