The Port_List Class

The Component class contains a Port_List (a linked list of pointers to ports) in the public section of its class. The Port_List class is almost identical to the Component_List class. As mentioned earlier, this similarity could be exploited using generic types or templates. Since C++ does not yet support templates, some code replication will be necessary.

The constructor and the add() methods are identical to the corresponding methods of the Component_List class with the exception that a pointer to a port rather than a pointer to a component is added to the list. The Port_List class is defined as follows:

class Port_List
{
public:
        Port_List();
        void            add(Port *);
        boolean         inputs_are_ready(ckt_time);
        boolean         is_lowest_level();
        void            descend();
private:
        Port_Node       *prt_list;
};

The default constructor is automatically called to initialize I_List and O_List when a Component object is constructed.

The other three methods, inputs_are_ready(), is_lowest_level() and descend() are specific to the simulation of the circuit and not to its description. As such, elaboration upon these methods will be deferred until the next chapter.