#403 – Equals Method vs. == Operator for Reference Types

In C#, you can compare two objects for equality by using the Equality operator (==) or by calling the Equals method.  In both cases, the default behavior for reference types is to check for reference equality, or identity.

    bool sameDog = yourDog.Equals(myDog);
    bool sameDog2 = yourDog == myDog;
    bool sameDog3 = Dog.Equals(yourDog, myDog);

By default, for a reference type, these mechanisms behave exactly the same way, implementing a reference equality check.  Under the covers, they are a bit different:

  • The Equals method is an instance method of the System.Object class.  It does some checks for null, but then uses the == operator in the default implementation.  It is a virtual method that you can override.
  • The == operator resolves to the CIL ceq instruction, which does a strict identity check.  You can override the == operator, in which case a new method named op_Equality is defined/called.

You can override Equals and the == operator independently.


About Sean
Software developer in the Twin Cities area, passionate about software development and sailing.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: