Mechanism: Type Extender


Type extenders enrich the set of interfaces supplied by a component.

Also Known As

Other well-known names for the mechanism, if any.


A scenario that illustrates a problem and how the different elements of the mechanism solve the problem. The scenario will help you understand the more abstract description of the mechanism below.


What are the situations in which the mechanism can be applied? What are examples of poor designs that the mechansim can address? How can you recognize these situations?


The elements participating in the mechanism and their responsibilities.


How the participants collaborate to carry out their responsibilities.


Benefits of type extenders include:

  1. Expanded standardized interface for alternative implementations; Other interfaces pass through to clients.

Type extenders have the following limitations:

  1. Fixed extensions.


What pitfalls, hints, or techniques should you be aware of when implementing the mechanism? Are there language-specific issues?

  1. Description of Bullet

Known Uses

Microsoft's OLE DB uses type extenders to expose a uniform set of interfaces for accessing information stores.

Related Mechanisms

What mechanisms are closely related to this one? What are the important differences? With which other mechanisms should this one be used?

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