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Is Structural Subtyping Useful? An Empirical Study

Summary: Is Structural Subtyping Useful?
An Empirical Study
Donna Malayeri and Jonathan Aldrich
Carnegie Mellon University, Pittsburgh, PA 15213, USA,
{donna, aldrich}@cs.cmu.edu
Abstract. Structural subtyping is popular in research languages, but all main-
stream object-oriented languages use nominal subtyping. Since languages with
structural subtyping are not in widespread use, the empirical questions of whether
and how structural subtyping is useful have thus far remained unanswered. This
study aims to provide answers to these questions. We identified several criteria
that are indicators that nominally typed programs could benefit from structural
subtyping, and performed automated and manual analyses of open-source Java
programs based on these criteria. Our results suggest that these programs could
indeed be improved with the addition of structural subtyping. We hope this study
will provide guidance for language designers who are considering use of this
subtyping discipline.
1 Introduction
Structural subtyping is popular in the research community and is used in languages such
as O'Caml [15], PolyToil [6], Moby [11], Strongtalk [5], and a number of type systems
and calculi (e.g., [7, 1]). In the research community, many believe that structural subtyp-


Source: Aldrich, Jonathan - School of Computer Science, Carnegie Mellon University


Collections: Computer Technologies and Information Sciences