An Empirical Study on Limits of Clone Unification Using Generics

Abstract. Generics (templates) attempt to unify similar program structures to avoid explosion of redundant code. How well do generics serve this purpose in practice? We try to answer this question through empirical analysis from two case studies. First, we analyzed the Java Buffer library in which 68 % of the code was redundant due to cloning. We were able to remove only 40 % of the redundant code using the proposed Java generics. Unification failed because the variations between cloned classes were either non-type parametric or nonparametric. To analyze whether this problem is specific to Java generics, we investigated the C++ Standard Template Library (STL), an exemplary application of C++ templates, as our second case study. Even though C++ templates are more powerful, we still found substantial cloning. We believe that we are dealing with a fundamental phenomenon that will cause many other class libraries and application programs to suffer from the code redundancy problem.