Working with Ada 9X classes

ABSTRACT

Ada 9X refines the Ada 83 concept of class and introduces class-wide types to support run-time polymorphism. We study how the Ada definition of class compares to other definitions of this term. We examine how run-time polymorphism is introduced in Ada 9X, how it relates to the different concepts of subtype, and how it compares with other forms of polymorphism. We also discuss the different uses of class-wide types, mainly as a means for dynamic binding (dispatching). However, since Ada 9X has adhered to the philosophy of building blocks, class-wide entities can be used for other purposes than dispatching. These uses are idioms that every programmer should be aware of. Some of these idioms are presented here. We also examine how classes are integrated with generics.

REFERENCES

• 1: Reference Manual of The Ada Programming Language. Washington, D.C.: Department of Defense, Ada Joint Program Office, Feb. 1983.
• 2: Ada 9X Mapping~evision Team. Ada 9X Reference Manual (Draft Version 5.0). Intermetrics, Inc., 733 Concord Avenue, Cambridge, Massachusetts 02138, MA, USA, June 1994. IR-MA-1363-3.
• 3: Stéphane Barbey , M. Kempe , A. Strohmeir, Advanced object-oriented features and programming in Ada 95, Tutorial proceedings on TRI-Ada '91: Ada's role in global markets: solutions for a changing complex world, p.359-489, November 05-10, 1995, Anaheim, California, United States [doi>10.1145/216591.216607]
• 4: S. Barbey and A. Strohmeier, The problematics of testing object-oriented software. In M. Ross, C. Brebbia, G. Staples, and J. Stapleton, editors, SQM '94 Second Conference on Software Quality Management, volume 2, pages 411-426, Edinburgh, Scotland, UK, July 26-28 1994.
• 5: J. Barnes, B. Brosgol, K. Dritz, O. Pazy, and B. Wichmann. Ada 9X Rationale (Draft Version 5. 0). intermetrics, inc., Cambridge, MA, USA, June 1994.
• 6: Gordon Blair , John Gallagher , David Hutchison , Doug Shepherd, Object-oriented languages, systems and applications, Halsted Press, New York, NY, 1991
• 7: Grady Booch, Object-oriented analysis and design with applications (2nd ed.), Benjamin-Cummings Publishing Co., Inc., Redwood City, CA, 1993
• 8: Gilad Bracha , William Cook, Mixin-based inheritance, Proceedings of the European conference on object-oriented programming on Object-oriented programming systems, languages, and applications, p.303-311, September 1990, Ottawa, Canada
• 9: Luca Cardelli , James Donahue , Lucille Glassman , Mick Jordan , Bill Kalsow , Greg Nelson, Modula-3 language definition, ACM SIGPLAN Notices, v.27 n.8, p.15-42, Aug. 1992 [doi>10.1145/142137.142141]
• 10: Luca Cardelli , Peter Wegner, On understanding types, data abstraction, and polymorphism, ACM Computing Surveys (CSUR), v.17 n.4, p.471-523, Dec. 1985 [doi>10.1145/6041.6042]
• 11: Gary J. Cernosek, ROMAN-9X: a technique for representing object models in Ada 9X notation, Proceedings of the conference on TRI-Ada '93, p.385-406, September 18-23, 1993, Seattle, Washington, United States [doi>10.1145/170657.170764]
• 12: Craig Chambers, Object-Oriented Multi-Methods in Cecil, Proceedings of the European Conference on Object-Oriented Programming, p.33-56, June 29-July 03, 1992
• 13: G. Dismukes and E. Ploedereder. Accidental overriding considered evil. Comment to the MRT 94-3955.a (ftp ajpo.sei.cmu.edu:/public/ada9x/mrtcommentsl 94.0302), Mar. 1992.
• 14: G. Eckert. Types, classes and collections in objectoriented analysis. In ICRE '94 First International Conference on Requirements Engineering, pages 32- 39, Colorado Springs, Colorado, USA, Apr. 18-22 1994.
• 15: Paul Hudak , Simon Peyton Jones , Philip Wadler , Brian Boutel , Jon Fairbairn , Joseph Fasel , María M. Guzmán , Kevin Hammond , John Hughes , Thomas Johnsson , Dick Kieburtz , Rishiyur Nikhil , Will Partain , John Peterson, Report on the programming language Haskell: a non-strict, purely functional language version 1.2, ACM SIGPLAN Notices, v.27 n.5, p.1-164, May 1992 [doi>10.1145/130697.130699]
• 16: J. Ichbiah , J. Barnes , R. Firth , M. Woodger, Rationale for the design of the Ada programming language, Cambridge University Press, New York, NY, 1981
• 17: Gregor Kiczales , Jim des Rivières , Daniel G. Bobrow, The art of metaobject protocol, MIT Press, Cambridge, MA, 1991
• 18: Gary T. Leavens , William E. Weihl, Reasoning about object-oriented programs that use subtypes, ACM SIGPLAN Notices, v.25 n.10, p.212-223, Oct. 1990
• 19: Barbara Liskov, Keynote address - data abstraction and hierarchy, Addendum to the proceedings on Object-oriented programming systems, languages and applications (Addendum), p.17-34, October 04-08, 1987, Orlando, Florida, United States
• 20: Barbara Liskov , Jeannette M. Wing, A New Definition of the Subtype Relation, Proceedings of the 7th European Conference on Object-Oriented Programming, p.118-141, July 26-30, 1993
• 21: Bertrand Meyer, Object-oriented software construction (2nd ed.), Prentice-Hall, Inc., Upper Saddle River, NJ, 1997
• 22: Bertrand Meyer, Eiffel: the language, Prentice-Hall, Inc., Upper Saddle River, NJ, 1992
• 23: H. M6ssenb6ck and N. Wirth. The programming language Oberon-2. Technical report, Institut fur Compustersysteme, ETH Zurich, Jan. 1992.
• 24: J. P. Rosen, What orientation should Ada objects take?, Communications of the ACM, v.35 n.11, p.71-76, Nov. 1992 [doi>10.1145/138844.138849]
• 25: Ed Seidewitz, Object-oriented programming with mixins in Ada, ACM SIGAda Ada Letters, v.XII n.2, p.76-90, March/April 1992 [doi>10.1145/142003.142009]
• 26: Bjarne Stroustrup, The C++ programming language (2nd ed.), Addison-Wesley Longman Publishing Co., Inc., Boston, MA, 1991
• 27: P. Wegner , S. B. Zdonik, Inheritance as an incremental modification mechanism or what like is and isn'tlike, on ECOOP '88 (European Conference on Object-Oriented Programming), p.55-77, August 1988, Oslo, Norway

INDEX TERMS

Primary Classification:
  D. Software
  D.3 PROGRAMMING LANGUAGES
      D.3.2 Language Classifications

          Nouns: Ada

Additional Classification:
  D. Software
  D.1 PROGRAMMING TECHNIQUES
      D.1.5 Object-oriented Programming
  D.3 PROGRAMMING LANGUAGES
      D.3.3 Language Constructs and Features
          Subjects: Procedures, functions, and subroutines

  F. Theory of Computation
  F.3 LOGICS AND MEANINGS OF PROGRAMS
      F.3.3 Studies of Program Constructs
          Subjects: Type structure; Functional constructs

General Terms:
Design, Languages