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    copied!<p>Two approaches immediately spring to mind:</p> <ol> <li><p>Do as Kevin suggested and write a struct that will serve as your key. Be sure to make this struct implement <code>IEquatable&lt;TKey&gt;</code> and to override its <code>Equals</code> and <code>GetHashCode</code> methods*.</p></li> <li><p>Write a class that utilizes nested dictionaries internally. Something like: <code>TripleKeyDictionary&lt;TKey1, TKey2, TKey3, TValue&gt;</code>... this class would internally have a member of type <code>Dictionary&lt;TKey1, Dictionary&lt;TKey2, Dictionary&lt;TKey3, TValue&gt;&gt;&gt;</code>, and would expose methods such as <code>this[TKey1 k1, TKey2 k2, TKey3 k3]</code>, <code>ContainsKeys(TKey1 k1, TKey2 k2, TKey3 k3)</code>, etc.</p></li> </ol> <p>*A word on whether overriding the <code>Equals</code> method is necessary: while it's true that the <code>Equals</code> method for a struct compares the value of each member by default, it does so by using reflection -- which inherently entails performance costs -- and is therefore <strong>not</strong> a very appropriate implementation for something that is meant to be used as a key in a dictionary (in my opinion, anyway). According to the MSDN documentation on <a href="http://msdn.microsoft.com/en-us/library/2dts52z7.aspx" rel="nofollow noreferrer"><code>ValueType.Equals</code></a>:</p> <blockquote> <p>The default implementation of the Equals method uses reflection to compare the corresponding fields of obj and this instance. Override the Equals method for a particular type to improve the performance of the method and more closely represent the concept of equality for the type.</p> </blockquote>
 

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