Examples of useful or non-trival dual interfaces

Posted by Scott Weinstein on Stack Overflow See other posts from Stack Overflow or by Scott Weinstein
Published on 2010-01-24T01:36:22Z Indexed on 2010/03/19 20:31 UTC
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Filed under:

category-theory

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system.reactive

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reactive-programming

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functional-programming

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c#

Recently Erik Meijer and others have show how IObservable/IObserver is the dual of IEnumerable/IEnumerator. The fact that they are dual means that any operation on one interface is valid on the other, thus providing a theoretical foundation for the Reactive Extentions for .Net

Do other dual interfaces exist? I'm interested in any example, not just .Net based.

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