research-article

Taming the wildcards: combining definition- and use-site variance

Authors:

Shan Shan Huang,

Yannis SmaragdakisAuthors Info & Claims

PLDI '11: Proceedings of the 32nd ACM SIGPLAN Conference on Programming Language Design and Implementation

Pages 602 - 613

https://doi.org/10.1145/1993498.1993569

Published: 04 June 2011 Publication History

Abstract

Variance allows the safe integration of parametric and subtype polymorphism. Two flavors of variance, definition-site versus use-site variance, have been studied and have had their merits hotly debated. Definition-site variance (as in Scala and C#) offers simple type-instantiation rules, but causes fractured definitions of naturally invariant classes; Use-site variance (as in Java) offers simplicity in class definitions, yet complex type-instantiation rules that elude most programmers.

We present a unifying framework for reasoning about variance. Our framework is quite simple and entirely denotational, that is, it evokes directly the definition of variance with a small core calculus that does not depend on specific type systems. This general framework can have multiple applications to combine the best of both worlds: for instance, it can be used to add use-site variance annotations to the Scala type system. We show one such application in detail: we extend the Java type system with a mechanism that modularly infers the definition-site variance of type parameters, while allowing use-site variance annotations on any type-instantiation.

Applying our technique to six Java generic libraries (including the Java core library) shows that 20-58 (depending on the library) of generic definitions are inferred to have single-variance; 8-63% of method signatures can be relaxed through this inference, and up to 91% of existing wildcard annotations are unnecessary and can be elided.

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Cited By

Binder DSkupin ILäwen DOstermann KAmin NIII H(2022)Structural refinement typesProceedings of the 7th ACM SIGPLAN International Workshop on Type-Driven Development10.1145/3546196.3550163(15-27)Online publication date: 6-Sep-2022
https://dl.acm.org/doi/10.1145/3546196.3550163
Mastrangelo LHauswirth MNystrom N(2019)Casting about in the dark: an empirical study of cast operations in Java programsProceedings of the ACM on Programming Languages10.1145/33605843:OOPSLA(1-31)Online publication date: 10-Oct-2019
https://dl.acm.org/doi/10.1145/3360584
Altidor JSmaragdakis Y(2014)Refactoring Java generics by inferring wildcards, in practiceACM SIGPLAN Notices10.1145/2714064.266020349:10(271-290)Online publication date: 15-Oct-2014
https://dl.acm.org/doi/10.1145/2714064.2660203
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Index Terms

Taming the wildcards: combining definition- and use-site variance
1. Software and its engineering
  1. Software notations and tools
    1. Formal language definitions
      1. Semantics
2. Theory of computation
  1. Semantics and reasoning
    1. Program semantics

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Published In

cover image ACM Conferences

PLDI '11: Proceedings of the 32nd ACM SIGPLAN Conference on Programming Language Design and Implementation

June 2011

668 pages

ISBN:9781450306638

DOI:10.1145/1993498

General Chair:
Mary Hall
University of Utah
,
Program Chair:
David Padua
University of Illinois at Urbana-Champaign

ACM SIGPLAN Notices Volume 46, Issue 6
PLDI '11
June 2011
652 pages
ISSN:0362-1340
EISSN:1558-1160
DOI:10.1145/1993316
Issue’s Table of Contents

Copyright © 2011 ACM.

Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected]

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Published: 04 June 2011

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PLDI '11: ACM SIGPLAN Conference on Programming Language Design and Implementation

June 4 - 8, 2011

California, San Jose, USA

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Cited By

Binder DSkupin ILäwen DOstermann KAmin NIII H(2022)Structural refinement typesProceedings of the 7th ACM SIGPLAN International Workshop on Type-Driven Development10.1145/3546196.3550163(15-27)Online publication date: 6-Sep-2022
https://dl.acm.org/doi/10.1145/3546196.3550163
Mastrangelo LHauswirth MNystrom N(2019)Casting about in the dark: an empirical study of cast operations in Java programsProceedings of the ACM on Programming Languages10.1145/33605843:OOPSLA(1-31)Online publication date: 10-Oct-2019
https://dl.acm.org/doi/10.1145/3360584
Altidor JSmaragdakis Y(2014)Refactoring Java generics by inferring wildcards, in practiceACM SIGPLAN Notices10.1145/2714064.266020349:10(271-290)Online publication date: 15-Oct-2014
https://dl.acm.org/doi/10.1145/2714064.2660203
Altidor JSmaragdakis YBlack AMillstein T(2014)Refactoring Java generics by inferring wildcards, in practiceProceedings of the 2014 ACM International Conference on Object Oriented Programming Systems Languages & Applications10.1145/2660193.2660203(271-290)Online publication date: 15-Oct-2014
https://dl.acm.org/doi/10.1145/2660193.2660203
Tardieu ONystrom NPeshansky ISaraswat V(2012)Constrained kindsACM SIGPLAN Notices10.1145/2398857.238467547:10(811-830)Online publication date: 19-Oct-2012
https://dl.acm.org/doi/10.1145/2398857.2384675
Tardieu ONystrom NPeshansky ISaraswat VLeavens GDwyer M(2012)Constrained kindsProceedings of the ACM international conference on Object oriented programming systems languages and applications10.1145/2384616.2384675(811-830)Online publication date: 19-Oct-2012
https://dl.acm.org/doi/10.1145/2384616.2384675
Altidor JReichenbach CSmaragdakis Y(2012)Java wildcards meet definition-site varianceProceedings of the 26th European conference on Object-Oriented Programming10.1007/978-3-642-31057-7_23(509-534)Online publication date: 11-Jun-2012
https://dl.acm.org/doi/10.1007/978-3-642-31057-7_23
Altidor JHuang SSmaragdakis Y(2011)Taming the wildcardsACM SIGPLAN Notices10.1145/1993316.199356946:6(602-613)Online publication date: 4-Jun-2011
https://doi.org/10.1145/1993316.1993569
Pearce DUtting MGroves L(2022)Verifying Whiley Programs with BoogieJournal of Automated Reasoning10.1007/s10817-022-09619-166:4(747-803)Online publication date: 20-Mar-2022
https://doi.org/10.1007/s10817-022-09619-1
Kumar SKumar R(2012)Precise static analysis for generic programs in object oriented languagesACM SIGSOFT Software Engineering Notes10.1145/2180921.218093737:3(1-6)Online publication date: 16-May-2012
https://dl.acm.org/doi/10.1145/2180921.2180937

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