CSC/ECE 517 Summer 2008/wiki2 8 jb

This wiki will explore the age old debate on inheritance vs. delegation, showing the strengths and weakness of each approach, and where each approach is preferred.

Background

An in-depth description Inheritance and Delegation is out of the scope of this wiki, but a brief discussion of each subject will help get us started.

Inheritance

Inheritance is one of the fundamental tenets of object oriented programming. Inheritance refers to the ability to model hierarchies classes that are related to each other through the is-a relationship. It is commonly agreed upon that inheritance done correctly must conform to the Liskov substitution principle.

Delegation

Delegation, sometimes referred to as aggregation, is the concept that one class may contain an instance of, or a reference to, another class, and delegate some responsibility to that class.

Aggregation can take on another connotation, specific to data modeling, closely related to composition. Composition refers to one class owning, and therefore being responsible for the memory allocation and deallocation, another class via the has-a relationship. In this context, aggregation refers to a class simply having a reference to another class, but not taking ownership.

For the purposes of this wiki, we will use the term delegation to mean that one class delegates responsibility to another class that it contains. In this context, the issue of ownership is irrelevant.

Links

Wikipedia: Inheritance
Wikipedia: Delegation
Wikipedia: Composition
Replace Inheritance With Delegation design pattern
Dr. Dobbs: Composition vs. Inheritance