SYSK 158: IComparable vs. IEquatable

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Both compare objects of types T…  So, which should your objects implement?

 

IComparable<T> specifies ordering, e.g. less than, equals, greater than.  String class implements IComparable<T> interface with its int CompareTo(T objectToCompare) function.  IEquatable<T> only tells you weather the objects are the equal or not via the bool Equals(T objectToCompare) function.

 

Below are the “rules of thumb” I follow:

  • Always implement IEquatable<T> interface for value types to avoid unnecessary boxing/unboxing of Object.Equals.
  • When implementing IEquatable<T>, also override Object.Equals.  After all, you want Equals to mean the same thing regardless of invocation method…
  • When providing custom implementation of equality, either by implementing IEquatable<T> or by overriding Object.Equals, also implement operator== and operator!=.
  • When implementing IComparable<T>, also implement IEquatable<T>
  • When implementing IComparable<T>, also implement operators <, >, <=, and >=.