Implementing a services lookup in C++

[kitfox]

I have a complex node network meant to display graphical information. There are many types of nodes, each derived from a base class Node.

Since the different nodes can present such a wide variety of information, I'd like to add a service lookup for each one. For example, if a node can be drawn, it will implement an IRenderable interface that provides drawing methods. If it has a bounding box, it will implement IBounds; if it can provide vertex information it will extend IVertex and so on. A program examining this graph should then be able to examine each node and query it to see if it provides the indicated service.

In Java this is pretty simple - you just need to use the instanceof operator to check if an object implements something. In C++, it seems to be a lot more complicated. I thought of using dynamic_cast, but wasn't sure if that would work if applied to a pointer of the base class. For example, if BoxNode extends Node and implements IBounds but Node does not implement IBounds, would 'bounds' be non null in the below code?

Node* n = new BoxNode();
IBounds* bounds = dynamic_cast<IBounds*>(n);

Anyhow, I came up with the below solution. It seems to work, but I'm not sure if it's the best way to go about this. I also feel ackward about using void *. Any thoughts on how best to go about this )or maybe if there's something better than a serices lookup) would be appreaciated.

class ServiceLookup
{
    QMap<std::type_index, void*> _serviceMap;

public:
    ServiceLookup()
    {}

    template <typename T>
    void registerService(T* service)
    {
        std::type_index idx = std::type_index(typeid(T));
        _serviceMap[idx] = service;
    }

    template <typename T>
    T* lookup() const
    {
        std::type_index idx = std::type_index(typeid(T));
        if (_serviceMap.contains(idx))
            return static_cast<T*>(_serviceMap[idx]);

        return nullptr;
    }

    void* lookup(std::type_index idx) const
    {
        if (_serviceMap.contains(idx))
            return _serviceMap[idx];

        return nullptr;
    }
};

[coder777]

For example, if BoxNode extends Node and implements IBounds but Node does not implement IBounds, would 'bounds' be non null in the below code?

What does 'implements IBounds' mean?
In C++ you inherit from base class(es). So neither 'extends' nor 'implements' exists as a term in C++ which I guess you know from java.

If you inherit from a class dynamic_cast will work.

I would suggest to have multiple objects instead of inheritance associated to a certain [unique] id. And why not use std::map<...>