Versioning, Virtual, and Override: "I can demonstrate to you a very real world versioning problem, one that indeed we see now from experience with Java. Whenever they ship a new version of the Java class libraries, breakage occurs. Whenever they introduce a new method in a base class, if someone in a derived class had a method of that same name, that method is now an override—except if it has a different return type, it no longer compiles. The problem is that Java, and also C++, does not capture the intent of the programmer with respect to virtual."