Abstract Increasing code reuse in software systems is an important way to decrease development and maintenance costs, reduce the time required to respond to new requirements, and significantly advance the feasible complexity limits for new systems. Object‐oriented programming languages and environments provide fundamental support for truly reusable code through abstraction, inheritance, and polymorphism. Reusable code is a prerequisite for a significantly more powerful concept: reusable design. Frameworks of resuable design abstractions are difficult to create and typically evolve over a long period of use and refinement. Thus, it is important to understand how systems evolve and how this evolution can be directed to achieve the best results. This article illustrates some of the standard transformations, called refactorings, that occur in object‐oriented systems as they evolve by describing the creation and evolution of a framework for building general‐purpose string‐to‐object translators. It reflects our experiences with object‐oriented compilers over a five year period while working on the Typed Smalltalk compiler project.

This paper describes a type system for Smalltalk that is type-safe, that allows most Smalltalk programs to be type-checked, and that can be used as the basis of an optimizing compiler.

TS (Typed Smalltalk) is a portable optimizing compiler that produces native machine code for a typed variant of Smalltalk, making Smalltalk programs much faster. This paper describes the structure of TS, the kinds of optimizations that it performs, the constraints that it places upon Smalltalk, the constraints placed upon it by an interactive programming environment, and its performance.