Handles: Behavior-propagating first class references for dynamically-typed languages

Abstract

Controlling object graphs and giving specific semantics to references (such as read-only, ownership, scoped sharing) has been the focus of a large body of research in the context of static type systems. Controlling references to single objects and to graphs of objects is essential to build more secure systems, but is notoriously hard to achieve in absence of static type systems. In this article we embrace this challenge by proposing a solution to the following question: What is an underlying mechanism that can support the definition of properties (such as revocable, read-only, lent) at the reference level in the absence of a static type system? We present handles: first-class references that propagate behavioral change dynamically to the object subgraph during program execution. In this article we describe handles and show how handles support the implementation of read-only references and revocable references. Handles have been fully implemented by modifying an existing virtual machine and we report their costs.