"Calum Grant" <calum@visula.org> 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.
I mean, a weak_ptr and optional both have 0 or 1 pointees, so there is at least a passing resemblance.
Merely a syntactic one. optional is not a smart pointer; it just uses * and -> to provide access to its contained object.
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. -- Dave Abrahams Boost Consulting www.boost-consulting.com