Dependent Types for Class-based Mutable Objects

We present an imperative object-oriented language featuring a dependent type system designed to support class-based programming and inheritance. Programmers implement classes in the usual imperative style, and may take advantage of a richer dependent type system to express class invariants and restrictions on how objects are allowed to change and be used as arguments to methods. By way of example, we implement insertion and deletion for binary search trees in an imperative style, and come up with types that ensure the binary search tree invariant. This is the first dependently-typed language with mutable objects that we know of to bring classes and index refinements into play, enabling types (classes) to be refined by indices drawn from some constraint domain. We give a declarative type system that supports objects whose types may change, despite being sound. We also give an algorithmic type system that provides a precise account of quantifier instantiation in a bidirectional style, and from which it is straightforward to read off an implementation. Moreover, all the examples in the paper have been run, compiled and executed in a fully functional prototype that includes a plugin for the Eclipse IDE

Dependent Types for Class-based Mutable Objects (Artifact)

This artifact is based on DOL, a Dependent Object-oriented Language featuring dependent types, mutable objects and class-based inheritance with subtyping. The typechecker written in Xtend, a flexible and expressive dialect of Java, is a direct implementation of the algorithmic type system described in the companion paper. It uses a direct interface to Z3 theorem prover via its API for Java. The artifact ships with an IDE developed as an Eclipse plugin based on the Xtext framework