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SMT-Based Checking of Predicate-Qualified Types for Scala

Type of publication Peer-reviewed
Publikationsform Proceedings (peer-reviewed)
Author Schmid Georg Stefan, Kuncak Viktor,
Project Developing Capacity for High-Productivity Large-Scale Computing
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Proceedings (peer-reviewed)

Title of proceedings Scala Symposium

Open Access

Type of Open Access Repository (Green Open Access)


We present qualified types for Scala, a form of refinement types adapted to the Scala language. Qualified types allow users to refine base types and classes using predicate expressions. We implemented a type checker for qualified types that is embedded in Scala's next-generation compiler Dotty and delegates constraint checking to an SMT solver. Our system supports many of Scala's functional as well as its object-oriented constructs. To propagate user-provided qualifier ascriptions we utilize both Scala's own type system and an incomplete, but effective qualifier inference algorithm. Our evaluation shows that for a series of examples exerting various of Scala's language features, the additional compile-time overhead is manageable. By combining these features we show that one can verify essential safety properties such as static bounds-checks while retaining several of Scala's advanced features.