DenkzeitWiki

Main /

Dynamic Dispatch

(weitergeleitet von Main.MultiMethods)

Polymorphism
AbstractDataType

• Wikipedia:Dynamic_dispatch

the process of mapping a message to a specific sequence of code (method) at runtime

• discriminate single dispatch, double dispatch and multiple dispatch:

Single Dispatch

The code to be invoked is determined by the type of the receiver of a message alone.
Common OOP is based upon single dispatch (see Polymorphism).

• Wiki:SingleDispatch

Double Dispatch

VisitorPattern In languages that do not support multiple dispatch one can achieve surrogate behavior by something called double dispatch:

1. dispatch to a method according to the runtime type of the object that recieves the message
2. that method dispatches according to the types of its arguments (rather explicitly)

• Wiki:DoubleDispatch
  • Wiki:DoubleDispatchExample
• Wikipedia:Double_dispatch

the visitor pattern simulates double dispatch in a conventional single-dispatch object-oriented language such as Java , Smalltalk, and C++.[1]

Multiple Dispatch

The code to be called is determined by the (runtime type of the) arguments of the method.
Such a method is called multimethod.

Making functions virtual with respect to more than one object[2]

• Wiki:MultipleDispatch

Overriding on all arguments. -> Overloading not needed. [3]

• Wikipedia:Multimethods

Multiple dispatch or multimethods is the feature of some object-oriented programming languages in which a function or method can be specialized on the type of more than one of its arguments.

Multimethods

• Wiki:MultiMethods
  • Wiki:ExternalPolymorphism
• http://www.artima.com/weblogs/viewpost.jsp?thread=101605 --Five-minute Multimethods in Python
• http://www-128.ibm.com/developerworks/library/l-pydisp.html --Charming Python: Multiple dispatch - Generalizing polymorphism with multimethods
  
  
• Origin of the term Multimethod from LtU
  • symmetric - like in CLOS
  • asymmetric - like in MultiJava
    • the first argument is more equal than the others
    • helpful in resolving ambiguities
  • encapsulated - like in Smalltalk [4] - class-oriented view on OOP
    • always asymmetric