Test Yourself Solution

This series of problems is really about knowing and recognizing the requirements for polymorphism but presented in a more authentic format. In the "real world," it will be rare for someone to ask you to list the requirements for polymorphism. On the other hand, as a practicing computer scientist, you must be able to read and understand the behavior of computer code, which includes recognizing when polymorphism is active and when it is not.

In summary, the requirements for polymorphism:

1. Inheritance: Child is a subclass of Parent, which satisfies the requirement for all twelve function calls
2. Function overriding: funcA and funcB in class Child overrides the functions with the same names in class Parent
3. Upcasting: Satisfied for P2 and P3
4. A pointer or reference variable: Satisfied for P1, P2, and C1
5. A virtual function: Satisfied for funcB

Solutions

class Parent
{
    public:
		void funcA() { . . . }
	virtual	void funcB() { . . . }
		void funcC() { . . . }
};


class Child : public Parent
{
    public:
		void funcA() { . . . }
	virtual	void funcB() { . . . }
};


int  main()
{
	Parent*	P1 = new  Parent;
	Parent*	P2 = new  Child;
	Child*	C1 = new  Child;
	Child	temp;
	Parent	P3 = temp;


	P1->funcA();	// (a) Parent: No upcast (Parent on both sides of the assignment operator)
	P1->funcB();	// (b) Parent: No upcast (Parent on both sides of the assignment operator)
	P1->funcC();	// (c) Parent: No upcast (Parent on both sides of the assignment operator)

	P2->funcA();	// (d) Parent: Not a virtual function (function determined by the pointer type)
	P2->funcB();	// (e) Child: All polymorphic requirements satisfied
	P2->funcC();	// (f) Parent: No function override (Child inherits funcC from Parent)

	C1->funcA();	// (g) Child: No upcast (Child on both sides of the assignment operator)
	C1->funcB();	// (h) Child: No upcast (Child on both sides of the assignment operator)
	C1->funcC();	// (i) Parent: No function override (Child inherits funcC from Parent)

	P3.funcA();	// (j) Parent: Not a pointer variable, so the assignment operation slices off all child features
	P3.funcB();	// (k) Parent: Not a pointer variable, so the assignment operation slices off all child features
	P3.funcC();	// (l) Parent: Not a pointer variable, so the assignment operation slices off all child features

	return 0;
}