Re: [boost] optional: Extending optional to hold derived values

From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2006-10-10 10:31:51

Vaclav Vesely wrote:
> Fernando Cacciola wrote:
> 
>>Vaclav Vesely wrote:
>>
>>>I would like to do somethink like this:
>>>
>>>    class Base {...}
>>>    class Derived: public Base {...}
>>>
>>>    optional<Base> x = Derived();
>>>    y->call_virtual_functions()
>>
>>It looks a lot like Boost.Any.
>>Have you looked at it?
> 
> 
> boost::any doesn't support derived classes as well. For example:
> 
> any x = Derived();
> any_cast<Base>(x).virtual_function(); // throws bad_any_cast
> 
> And moreover boost::any is too general. I want to store only values of Base 
> and its derived classes.

Perhaps you can use Boost.PtrContainer:

typedef boost::ptr_vector< boost::nullable<Base> > OptionalContainer;

?

-Thorsten