C++ for Scientists - Technische Universität Dresden

220 CHAPTER 7. EFFECTIVE PROGRAMMING: THE POLYMORPHIC WAY
Note
The binary method problem is encountered when methods in which the
receiver type and argument type should vary together, such as equality
comparisons, must instead use a fixed formal parameter type to
maintain type safety. The problem arises in mainstream object-oriented
languages because only the receiver of a method call is used for run time
method selection, and so the argument must be assumed to have the
most general possible type. Existing techniques to solve this problem
require intricate coding patterns that are tedious and error-prone. The
binary method problem is a prototypical example of a larger class of
problems where overriding methods require type information for their
formal parameters. Another common example of this problem class is
the implementation of event handling (e.g., for graphical user interfaces),
where ”callback methods” must respond to a variety of event
types.