SYSK 158: IComparable vs. IEquatable

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 >=.

Comments

• Anonymous
  July 18, 2006
  PingBack from http://microsoft.wagalulu.com/2006/07/18/sysk-158-icomparablet-vs-iequatablet/
• Anonymous
  July 18, 2006
  A Visual Studio 2005 code snippet that implements a skeleton value type adhering the Framework Design Guidelines.
• Anonymous
  September 22, 2007
  I posted an article on why it is important to override the Object.Equals method when implementing the IEquatable interface on codeproject (http://www.codeproject.com/useritems/IEquatable.asp).