Multiple Dispatch
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This document discusses different types of dispatch in object-oriented programming. It explains static dispatch, single dispatch, and multiple dispatch. Multiple dispatch allows method lookup to be based on the runtime classes of parameters rather than their static types. It can be emulated using the visitor pattern and resembles pattern matching. The document also lists advantages of multiple dispatch like natural interaction with overloading, but notes disadvantages like potential confusion and ambiguity due to the "diamond problem". It discusses how the CZ language implements multiple dispatch across inheritance hierarchies without diamonds.
Multiple Dispatch
- 2. Motivation void f(String o) { ... } void f(Object o) { ... } Object o = new String("foo"); f(o); Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 2 / 8
- 3. Motivation void f(String o) { ... } void f(Object o) { ... } Object o = new String("foo"); f(o); Invoked function may change with the static type of o. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 2 / 8
- 4. Types of Dispatch Static dispatch. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 3 / 8
- 5. Types of Dispatch Static dispatch. Single dispatch. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 3 / 8
- 6. Types of Dispatch Static dispatch. Single dispatch. Multiple dispatch. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 3 / 8
- 7. Types of Dispatch Static dispatch. Single dispatch. Multiple dispatch. . . . Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 3 / 8
- 8. Multiple Dispatch Method lookup is based on runtime classes of parameters. Does not depend on static types of parameters. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 4 / 8
- 9. Multiple Dispatch Method lookup is based on runtime classes of parameters. Does not depend on static types of parameters. Can be emulated (albeit in a restricted fashion) by the visitor pattern. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 4 / 8
- 10. Multiple Dispatch Method lookup is based on runtime classes of parameters. Does not depend on static types of parameters. Can be emulated (albeit in a restricted fashion) by the visitor pattern. Resembles (in a way) pattern matching. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 4 / 8
- 11. Advantages More natural interaction with overloading. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 5 / 8
- 12. Advantages More natural interaction with overloading. More equal parameters. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 5 / 8
- 13. Advantages More natural interaction with overloading. More equal parameters. Better composability. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 5 / 8
- 14. Disadvantages May be slightly confusing. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 6 / 8
- 15. Disadvantages May be slightly confusing. Blurred notion of method containment. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 6 / 8
- 16. Disadvantages May be slightly confusing. Blurred notion of method containment. The diamond problem may cause ambiguity. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 6 / 8
- 17. CZ Multiple dispatch only works across inheritance hierarchy (not across requires hierarchy). Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 7 / 8
- 18. CZ Multiple dispatch only works across inheritance hierarchy (not across requires hierarchy). No diamonds in inheritance hierarchy. Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 7 / 8
- 19. See Malayeri, D. and Aldrich, J. CZ: Multiple Inheritance Without Diamonds. Proceeding of the 24th ACM SIGPLAN Conference on Object Oriented Programming Systems Languages and Applications. 21–40. http://doi.acm.org/10.1145/1640089.1640092 Michal P´ıˇse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 8 / 8