Copy and paste redeemed

Software development relies critically on code reuse, which software engineers typically realise through handwritten abstractions, such as functions, methods, or classes. However, such abstractions can be challenging to develop and maintain. One alternative form of re-use is copy-paste-modify, a methodology in which developers explicitly duplicate source code to adapt the duplicate for a new purpose. We have found that copy-paste-modify can be substantially faster than manual abstraction, and past research strongly suggests that it is a popular technique among software developers. We therefore propose that software engineers should forego hand-written abstractions in favour of copying and pasting. However, empirical evidence shows that copy-paste-modify complicates software maintenance, leading to bugs. To address this concern, we propose a software tool that merges together similar pieces of code and automatically creates suitable abstractions. This allows software developers to get the best of both worlds: custom abstraction together with easy re-use. To demonstrate the feasibility of our approach, we have implemented and evaluated a prototype merging tool for C++ on a number of near-clones in popular Open Source packages. We define near-clones as any set of method definitions that differ from each other in a few AST nodes. We found that maintainers find our algorithmically created abstractions to be largely preferable to existing duplicated code.