If you wish to make a class comparable with type T then you should both make a CompareTo(T) method and inherit from the IComparable<T> interface. If a CompareTo(T) method has been added without the interface also being implemented, it is sometimes an indication that the programmer has forgotten to inherit the interface despite providing the implementation for it.

The problem can be easily resolved by making the class implement IComparable<T> (either directly or indirectly).

In this example, the developer has implemented a CompareTo(Bad) method, but has forgotten to add the corresponding IComparable<Bad> interface.

In the revised example, the interface is added.
  • MSDN: IComparable Interface
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