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    copied!<p>I would generally recommend against implementing IEquatable&lt;T&gt; on any non-sealed class, or implementing non-generic IComparable on most, but the same cannot be said for IComparable&lt;T&gt;. Two reasons:</p> <ol> <li>There already exists a means of comparing objects which may or may not be the same type: Object.Equals. Since IEquatable&lt;T&gt; does not include GetHashCode, its behavior essentially has to match that of Object.Equals. The only reason for implementing IEquatable&lt;T&gt; in addition to Object.Equals is performance. IEquatable&lt;T&gt; offers a small performance improvement versus Object.Equals when applied to sealed class types, and a big improvement when applied to structure types. The only way an unsealed type's implementation of IEquatable&lt;T&gt;.Equals can ensure that its behavior matches that of a possibly-overridden Object.Equals, however, is to call Object.Equals. If IEquatable&lt;T&gt;.Equals has to call Object.Equals, any possible performance advantage vanishes. <li>It is sometimes possible, meaningful, and useful, for a base class to have a defined natural ordering involving only base-class properties, which will be consistent through all subclasses. When checking two objects for equality, the result shouldn't depend upon whether one regards the objects as being a base type or a derived type. When ranking objects, however, the result should often depend upon the type being used as the basis for comparison. Derived-class objects should implement IComparable&lt;TheirOwnType&gt; but should not override the base type's comparison method. It is entirely reasonable for two derived-class objects to compare as "unranked" when compared as the parent type, but for one to compare above the other when compared as the derived type. </ol> <p>Implementation of non-generic IComparable in inheritable classes is perhaps more questionable than implementation of IComparable&lt;T&gt;. Probably the best thing to do is allow a base-class to implement it if it's not expected that any child class will need some other ordering, but for child classes not to reimplement or override parent-class implementations.</p>
 

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