Code Anystate

The Anystate abstraction found in anystate.h can be used for storing and restoring the state of a object, without knowing the exact class of the object.

In Daisy, we often divide code into three classes:

1. A component provides a generic interface to a particular concept we want to model, might a be a specific physical process.
2. A model implements the interface, and would typically be a specific mathematical description of the physical process.
3. Client code can only access instances of the models through the component interface.

This separation allows us in theory (and occasionally also in practice) to introduce new models to Daisy without altering the existing client code.

The Anystate abstraction allows of to save the state of a model, without violating the component interface boundary.

Component responsibility

A typical component interface to Anystate could be 

virtual Anystate get_state () const = 0; 
virtual void set_state (const Anystate&) = 0;

Client responsibility

The client can use Anystate object in the component interface, and to make copies, and nothing else. The client is also responsible for assure that the Anystate objects are only used with the same model (in practice, model instance) as they originate from. 

void example (Component& instance)     
      {      
         const Anystate old_state = instance.get_state ();      
         instance.manipulate ();       
         Anystate new_state = old_state;       
         instance.set_state (old_state);     
      }

Model responsibility

The model should declare a new class derived from Anystate::Content which can contain the state of the model, and implements the 'clone' method for making a copy of itself.

The model can then the constructor to Anystate that accepts an std::auto_ptr<Anystate::Content> to create the Anystate instance, and the Anystate::inpect function to retrieve the content again. Use dynamic_cast to convert it to the right type.