#405 – Equals Method for Equivalence, == Operator for Identity

You can check for equality between two objects by calling the Equals method or by using the == operator.  There are some differences between how the methods work, but both Equals and == can be overloaded in a user-defined type.

You can therefore change the behavior of one of these methods, or both.  The question is–how should these two behaviors work for a custom class?

Roughly speaking, the desired behavior, from a client’s point of view is:

  • Use Equals method to determine value equality, or equivalence–do the two objects represent the same thing?
  • Use == operator to determine reference equality, or identity–do the two references point to exactly the same object?

This argues for overloading Equals for a user-defined reference type, but not overloading the == operator.

This would result in the following behavior:

            Dog d1 = new Dog("Lassie", 7);
            Dog d2 = new Dog("Lassie", 7);

            bool bValueEquality = d1.Equals(d2);    // true
            bool bRefEquality = d1 == d2;    // false
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About Sean
Software developer in the Twin Cities area, passionate about .NET technologies. Equally passionate about my own personal projects related to family history and preservation of family stories and photos.

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