Abstract
Programmers often need to initialise circular structures of objects. Initialisation should be safe (so that programs can never suffer null pointer exceptions or otherwise observe uninitialised values) and modular (so that each part of the circular structure can be written and compiled separately). Unfortunately, existing languages do not support modular circular initialisation: programmers in practical languages resort to Tony Hoare’s “Billion Dollar Mistake”: initialising variables with nulls, and then hoping to fix them up afterward. While recent research languages have offered some solutions, none fully support safe modular circular initialisation.
We present placeholders, a straightforward extension to object-oriented languages that describes circular structures simply, directly, and modularly. In typed languages, placeholders can be described by placeholder types that ensure placeholders are used safely. We define an operational semantics for placeholders, a type system for placeholder types, and prove soundness. Incorporating placeholders into object-oriented languages should make programs simultaneously simpler to write, and easier to write correctly.
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References
Birka, A., Ernst, M.D.: A practical type system and language for reference immutability. In: OOPSLA, pp. 35–49 (2004)
Bracha, G.: Executable grammars in Newspeak. In: JAOO (2007)
Bracha, G., von der Ahé, P., Bykov, V., Kashai, Y., Maddox, W., Miranda, E.: Modules as objects in Newspeak. In: D’Hondt, T. (ed.) ECOOP 2010. LNCS, vol. 6183, pp. 405–428. Springer, Heidelberg (2010), http://dl.acm.org/citation.cfm?id=1883978.1884007
Counsell, S., Loizou, G., Najjar, R.: Evaluation of the ‘replace constructors with creation methods’ refactoring in Java systems. IET Software 4(5), 318–333 (2010)
Fähndrich, M., Xia, S.: Establishing object invariants with delayed types. In: OOPSLA. pp. 337–350 (2007)
Fowler, M.: Refactoring: Improving the Design of Existing Code. Addison-Wesley (2000)
Gamma, E., Helm, R., Johnson, R.E., Vlissides, J.M.: Design Patterns: Elements of Reusable Object-Oriented Software. Addison-Wesley Professional Computing Series. Addison-Wesley (1995)
Gil, J(Y.), Shragai, T.: Are we ready for a safer construction environment? In: Drossopoulou, S. (ed.) ECOOP 2009. LNCS, vol. 5653, pp. 495–519. Springer, Heidelberg (2009)
Gordon, C.S., Parkinson, M.J., Parsons, J., Bromfield, A., Duffy, J.: Uniqueness and reference immutability for safe parallelism. In: OOPSLA, pp. 21–40 (2012)
Haack, C., Poll, E.: Type-based object immutability with flexible initialization. In: Drossopoulou, S. (ed.) ECOOP 2009. LNCS, vol. 5653, pp. 520–545. Springer, Heidelberg (2009)
Hoare, C.A.R.: The emperor’s old clothes. Comm. ACM 24(2) (February 1981)
Hoare, C.: Null references: The billion dollar mistake (March 2009), abstract of QCon London Keynote qconlondon.com/london-2009/presentation/Null+References:+The+Billion+Dollar+Mistake
Igarashi, A., Pierce, B.C., Wadler, P.: Featherweight Java: A minimal core calculus for Java and GJ. In: OOPSLA, pp. 132–146 (1999)
Leroy, X.: The Objective Caml system (release 2.00) (August 1998), http://paulliac.inria.fr/caml
Oliveira, B.C.d.S., Cook, W.R.: Extensibility for the masses - practical extensibility with object algebras. In: Noble, J. (ed.) ECOOP 2012. LNCS, vol. 7313, pp. 2–27. Springer, Heidelberg (2012)
Qi, X., Myers, A.C.: Masked types for sound object initialization. In: POPL, pp. 53–65 (2009)
Servetto, M., Mackay, J., Potanin, A., Noble, J.: The billion dollar fix: Safe modular circular initialisation with placeholders and placeholder types. Tech. Rep. 12-25, ECS, VUW (2012), http://ecs.victoria.ac.nz/Main/TechnicalReportSeries
Servetto, M., Potanin, A.: Our billion dollar fix. Tech. Rep. 12-19, ECS, VUW (2012), http://ecs.victoria.ac.nz/Main/TechnicalReportSeries
Summers, A.J., Müller, P.: Freedom before commitment - a lightweight type system for object initialisation. In: OOPSLA, pp. 1013–1032 (2011)
Syme, D.: Initializing mutually referential abstract objects: The value recursion challenge. Electronic Notes in Theoretical Computer Science 148(2), 3–25 (2006)
Zibin, Y., Cunningham, D., Peshansky, I., Saraswat, V.: Object initialization in X10. In: Noble, J. (ed.) ECOOP 2012. LNCS, vol. 7313, pp. 207–231. Springer, Heidelberg (2012)
Zibin, Y., Potanin, A., Artzi, S., Kiezun, A., Ernst, M.D.: Object and reference immutability using Java generics. In: Foundations of Software Engineering (2007)
Zibin, Y., Potanin, A., Li, P., Ali, M., Ernst, M.D.: Ownership and immutability in generic Java. In: OOPSLA, pp. 598–617 (2010)
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Servetto, M., Mackay, J., Potanin, A., Noble, J. (2013). The Billion-Dollar Fix. In: Castagna, G. (eds) ECOOP 2013 – Object-Oriented Programming. ECOOP 2013. Lecture Notes in Computer Science, vol 7920. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-39038-8_9
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DOI: https://doi.org/10.1007/978-3-642-39038-8_9
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