Fighting bit Rot with Types (Experience Report: Scala Collections)

We report on our experiences in redesigning Scala's collection libraries, focussing on the role that type systems play in keeping software architectures coherent over time. Type systems can make software architecture more explicit but, if they are too weak, can also cause code duplication. We show that code duplication can be avoided using two of Scala's type constructions: higher-kinded types and implicit parameters and conversions.