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

6 Oct 2006


      Vaclav Vesely wrote:
...
Hi,
I would like to do somethink like this:
class Base {...}
    class Derived: public Base {...}
optional<Base> x = Derived();
    y->call_virtual_functions()
Current design of boost::optional doesn'g support this. But I wonder if it's 
to possible to extend it.
I created simple prototype to verify the technique (see attachment). It 
works this way:
optional<BaseT>
- has attribut _value_holder of type value_holder<BaseT>*
- _value_holder points to the instance of derived_value_holder<BaseT, 
DerivedT>, where DerivedT is the type of stored value
It looks a lot like Boost.Any.
Have you looked at it?

Fernando Cacciola
SciSoft
http://fcacciola.50webs.com