TITLE: Bad global object initialization schemes

[ This material comes from "C++ Strategies and Tactics" by
  Robert B. Murry, p. 127 ]

	class Base {
	  public:
	    void foo ();
	};

	class Derived : public Base {
	  public:
	    void foo ();
	};

	main () {
	    Derived d;
	    d.foo ();   // calls Derived::foo

	    Base& b(d);
	    b.foo ();   // calls Base::foo
	}

It is very bad practice for a program to deliberately exploit this
behavior. The whole idea of inheritance is that the object, not the
caller, knows the implementation of a particular operation. A program
that depends on different implementations being chosen based on how the
operation was called is using the type system to control part of the
implementation of the program -- and in a very subtle way.

[ Guide actually breaks this rule for one very restricted case -
  to provide a type specific access method. For example,

	TCommonGraph*    TCommonNode::parentGraph ();
	TSESDesignGraph* TSESDesignNode::parentGraph ();

  Both implementations of these use the same logic, but "wrap up"
  the cast to the correct derived type. ]