Enforcing Resource Usage Protocols via Scoped Methods∗

Traditional modularity mechanisms such as Java’s classes and packages or ML’s structures and functors restrict the set of functions that may be applied to an object, but are unable to restrict the timing of these function applications effectively. We propose a new language construct, the scoped method, which allows the implementer of a class to specify a temporal resource usage protocol. This protocol limits the sequence of methods that may be applied to an object. For example, a protocol for file access might specify that the file must be opened, read or written some number of times, and then closed. We present a type-based analysis to enforce the protocol and prove its correctness.