See [Kim 89, ch 1,3].
This is the 1 Level System as Described under Meta-Classes. Delegation refers to the delegating of responsibility and can be applied to inheritance. When a derived class does not have a desired attribute, it "delegates" responsibility to one of its base classes. In delegation systems, each object has a delegate list instead of a parent list. Thus, delegation's primary emphasis is on message passing where an object could delegate responsibility of a message it couldn't handle to objects that potentially could (its delegates). Any object can be added to the delegate list, giving dynamic inheritance (of a sort). Typically, delegation and prototyping languages also have "part inheritance" in which fields and methods can be added and deleted from objects. This makes for easy "prototyping", which allows for objects to be constructed piece by piece at run-time, although the term "prototyping" in the context of delegation languages usually refers to objects serving as prototypes for object instantiation, or exemplars.
Next's NextStep OS provides delegation using Objective-C, providing an example of delegation in a class-based language [Garfinkel 93].
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