Design by Contract: Making Object-Oriented Programs that Work

Abstract

To deliver on its promises, object-oriented technology must be able to produce systems that are reliable (correct and robust). Only under these conditions will the other quality factors advertised for the method, in particular the increase in reusability and extendibility, yield the expected benefits for software practitioners. It is indeed possible to use object-oriented technology to produce, almost routinely, software systems that reach a degree of reliability without any equivalent in conventional methods, languages and tools. This requires a strict application of pure object-oriented concepts, in particular, seamlessness (the use of a consistent method and notation throughout the software life-cycle), information hiding, automatic garbage collection, static typing, and the combination of static typing and dynamic binding. Another key component of this approach is the notion of design by contract, which leads to the production of systems whose correctness is built-in rather than ensured ex post facto.