Static composition of refactorings

  • Authors:

  • Günter Kniesel;Helge Koch

  • Affiliations:

  • Institute of Computer Science III, University of Bonn, Römerstr. 164, D-53117 Bonn, Germany;Technisch-mathematische studiengesellschaft mbH, Holtorfer Strasse 54, 53229 Bonn, Germany and Institute of Computer Science III, University of Bonn, Römerstr. 164, D-53117 Bonn, Germany

  • Venue:
  • Science of Computer Programming - Special issue on program transformation
  • Year:
  • 2004

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Abstract

The number of possible refactorings is unlimited, so no tool vendor will ever be able to provide custom refactorings for all specific user needs. Therefore, we propose a new kind of refactoring tools, which allow users to create, edit and compose required refactorings just like any other documents. The heart of such a refactoring editor is the ability to compose larger refactorings from existing ones. Computing the precondition of the composite refactoring from the preconditions of the composed refactorings is non-trivial since earlier transformations influence the truth of preconditions of later ones. The ability to calculate these effects without referring to a particular program to which the refactorings should be applied is called program-independent composition. It is the prerequisite for creating composite refactorings that are reusable on arbitrary programs. The main contribution of this paper is a formal model for automatic, program-independent composition of conditional program transformations. We show that conditional transformations, including refactorings, can be composed flom a limited set of basic operations. Program-independent derivation of a precondition for the composite is based on the notion of "transformation description", which can be seen as a simplified, yet equally powerful, variant of Roberts' "postconditions" (Practical analysis for refactoring, Ph.D. Thesis (1999)). Our approach simplifies the implementation of refactoring tools--only the basic operations and the ability for composition must be hard coded in a tool. As a proof of concept, we sketch a transformation framework that implements our approach (jConditioner) and, based on the framework, an experimental refactoring tool (ConTraCT) that includes the editing capabilities that motivated our work.