The Problem with Substitution

class Window {
public:
	virtual void oops();
private:
	int height;
	int width;
};

class TextWindow : public Window {
public:
	virtual void oops();
private:
	char * contents;
	int cursorLocation;
};

	Window x; // how much space to set aside?
	TextWindow y;
	x = y; // what should happen here?