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"Practical Predicate Dispatch"
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Practical Predicate Dispatch
Ballroom A-B
Thursday, 10:30, 30 minutes | 7 | · | 8 | · | 9 | · | 10 | · | 11 | · | 12 | · | 13 | · | 14 | · | 15 | · | 16 | · | 17 | · | 18 | · | 19 | · | 20 | · | 21 |
Todd Millstein, University of California, Los Angeles
Predicate dispatch is an object-oriented (OO) language mechanism for
declaratively determining the method implementation to be invoked upon
a message send. With predicate dispatch, each method implementation
includes a predicate guard specifying the conditions under which the
method should be invoked, and logical implication of predicates
determines the method overriding relation. Predicate dispatch
naturally unifies and generalizes disparate forms of dynamic dispatch,
including traditional OO dispatch, multimethod dispatch, and
functional-style pattern matching. Despite the promise of predicate
dispatch, prior languages supporting predicate dispatch have had
several deficiencies that limit its utility in practice.
We introduce JPred, a practical, backward-compatible extension to Java
supporting predicate dispatch. While prior languages with predicate
dispatch have been extensions to toy or non-mainstream languages, we
show how predicate dispatch can be naturally added to a traditional OO
language. While prior languages with predicate dispatch have required
the whole program to be available for typechecking and compilation,
JPred retains Java's encapsulation properties and modular typechecking
and compilation strategies. While prior languages with predicate
dispatch have devised special-purpose algorithms for reasoning about
predicates, JPred employs general-purpose, off-the-shelf decision
procedures. As a result, JPred's type system is more flexible,
allowing several useful programming idioms that are spuriously
rejected by those other languages. After describing the JPred
language and type system, we present a case study illustrating the
utility of JPred in a real-world application, including its use in the
detection of several bugs.
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