multiple dispatch

Motivation

void f(String o) { ... }void f(Object o) { ... }

Object o = new String("foo");

Invoked function may change with the static type of o.

Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 2 / 8

Motivation

void f(String o) { ... }void f(Object o) { ... }

Object o = new String("foo");

Invoked function may change with the static type of o.

Types of Dispatch

Static dispatch.

Single dispatch.

Multiple dispatch.

Types of Dispatch

Static dispatch.

Single dispatch.

Multiple dispatch.

Types of Dispatch

Static dispatch.

Single dispatch.

Multiple dispatch.

Types of Dispatch

Static dispatch.

Single dispatch.

Multiple dispatch.

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.

Multiple Dispatch

Advantages

More natural interaction with overloading.

More equal parameters.

Better composability.

Advantages

Disadvantages

May be slightly confusing.

Blurred notion of method containment.

The diamond problem may cause ambiguity.

Disadvantages

Multiple dispatch only works across inheritance hierarchy (not acrossrequires hierarchy).

No diamonds in inheritance hierarchy.

Multiple dispatch only works across inheritance hierarchy (not acrossrequires hierarchy).

No diamonds in inheritance hierarchy.

Malayeri, D. and Aldrich, J. CZ: Multiple Inheritance WithoutDiamonds. Proceeding of the 24th ACM SIGPLAN Conference on ObjectOriented Programming Systems Languages and Applications. 21–40.http://doi.acm.org/10.1145/1640089.1640092

multiple dispatch

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