Today Mads shows us a not well known class that is called a Triplet. He also asks a question: how you would use it. Fortunately I have seen this class before so here is what I have learned:
Triplet is used in the same way as a Pair class - mostly in the LoadViewState and SaveViewState methods. Generally if you are saving view state in your control you not only have to store your data, but also the data returned by the call to the base.SaveViewState method. This is where the Pair class or the Triplet come in handy since given two (three) fields, one is used for the base control's state and the other can be used by your state. Similarly, when loading the state in the LoadViewState method you get your own state from one of the fields, and pass the other to the base class'es LoadViewState method. You have to remember to pass the same field you have used in the SaveViewState method or the things will go nasty 
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Triplet is used when Pair is not enough. If Triplet is not enough, you have to create your own class.
I hope this sheds some light on the topic.