Delegation (programming)

Delegation (programming)

In object-oriented programming, there are three related notions of delegation.

• Most commonly, it refers to a programming language feature making use of the method lookup rules for dispatching so-called self-calls as defined by Lieberman in his 1986 paper "Using Prototypical Objects to Implement Shared Behavior in Object-Oriented Systems". Delegation as a language feature supports the prototype-based programming model.
• In its original usage, delegation refers to one object relying upon another to provide a specified set of functionalities. In research, this is often referred to as consultation or as aggregation in modeling.
• In CLI, a delegate is a form of type-safe function pointer usually used in an observer pattern as a means telling which method to call when an event is triggered, keeping the method type.

Despite delegation being fairly widespread, relatively few major programming languages implement delegation as an alternative model to static inheritance. The Self programming language incorporates the notion of delegation through its notion of mutable parent slots that are used upon method lookup on self calls.

In object-oriented programming, a multicast delegate is a delegate that points to several methods. Multicast delegation is a mechanism that provides functionality to execute more than one method. There is a list of delegates maintained internally, and when the multicast delegate is invoked, the list of delegates is executed.