#404 – Equals Method vs. == Operator for Value Types

In C#, you can compare two objects for equality by using the Equality operator (==) or by calling the Equals method.  For built-in value types, the default behavior checks for value equality, or equivalence.

            int i1 = 42;
            int i2 = 42;

            bool check1 = i1 == i2;      // true
            bool check2 = i1.Equals(i2);  // true
            bool check3 = int.Equals(i2, i2);  // true

For the predefined value types (e.g. int, float):

  • The Equals method performs a value equality check
  • The == operator resolves to the CIL ceq instruction, which does a strict identity check

For user-defined struct types:

  • The Equals method implementation performs a value equality check by comparing each field of the struct (using reflection).  You can (and should) override Equals to provide an implementation specific to the struct.
  • The == operator is undefined, unless you override it in the struct.

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

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