Post on 22-Nov-2014
description
transcript
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 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");
f(o);
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
Types of Dispatch
Static dispatch.
Single dispatch.
Multiple dispatch.
. . .
Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 3 / 8
Types of Dispatch
Static dispatch.
Single dispatch.
Multiple dispatch.
. . .
Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 3 / 8
Types of Dispatch
Static dispatch.
Single dispatch.
Multiple dispatch.
. . .
Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 3 / 8
Types of Dispatch
Static dispatch.
Single dispatch.
Multiple dispatch.
. . .
Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 3 / 8
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 Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 4 / 8
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 Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 4 / 8
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 Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 4 / 8
Advantages
More natural interaction with overloading.
More equal parameters.
Better composability.
Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 5 / 8
Advantages
More natural interaction with overloading.
More equal parameters.
Better composability.
Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 5 / 8
Advantages
More natural interaction with overloading.
More equal parameters.
Better composability.
Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 5 / 8
Disadvantages
May be slightly confusing.
Blurred notion of method containment.
The diamond problem may cause ambiguity.
Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 6 / 8
Disadvantages
May be slightly confusing.
Blurred notion of method containment.
The diamond problem may cause ambiguity.
Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 6 / 8
Disadvantages
May be slightly confusing.
Blurred notion of method containment.
The diamond problem may cause ambiguity.
Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 6 / 8
CZ
Multiple dispatch only works across inheritance hierarchy (not acrossrequires hierarchy).
No diamonds in inheritance hierarchy.
Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 7 / 8
CZ
Multiple dispatch only works across inheritance hierarchy (not acrossrequires hierarchy).
No diamonds in inheritance hierarchy.
Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 7 / 8
See
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
Michal Pıse (CTU in Prague) Object Programming L. 6: Multiple Dispatch November 2, 2010 8 / 8