Make interchangeable class types via pointer casting only, without having to allocate any new objects?

Question

UPDATE: I do appreciate \"don\'t want that, want this instead\" suggestions. They are useful, especially when provided in context of the motivating scenari

Answer 1

The term Accessor is a dead giveaway: what you are looking for is a Proxy.

There is no reason for a Proxy not to be passed around by value.

// Let us imagine that NodeBase is now called Node, since there is no inheritance

class AccessorFoo {
public:
    AccessorFoo(Node& n): node(n) {}

    int bar() const { return node->bar; }

private:
    std::reference_wrapper node;
};

And then you can freely convert from one accessor to another... though this smells. Normally the very goal of having an accessor is to restrict access in a way, so casting nilly willy to another accessor is bad. However one could support casting to a narrower accessor.