In this paper, techniques are presented that exploit two design patterns, the Visitor\udpattern and the Decorator pattern, to automatically validate invariants about the data\udattributes in a C++ class. To investigate the pragmatics involved in using the two\udpatterns, a study of an existing, well-tested application, keystone, a parser and frontend\udfor the C++ language, is presented. Results from the study indicate that these two\udpatterns provide flexibility in terms of the frequency and level of granularity of validation\udof the class invariants, which are expressed in the Object Constraint Language, OCL. The\udquantitative results measure the impact of these approaches and the additional faults\uduncovered through validation of the case study.
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