#795 – Rules for Creating an Immutable Class

There are times when it’s desirable to make a class immutable–meaning that client code cannot change any of the class’ data, after an instance of the class is created.

To create an immutable class:

• Pass all the data that the class requires into a constructor
• Make a copy of any mutable data type passed into the constructor
• Make all properties read-only
• Remove all public fields or make them readonly
• Ensure that no methods change any of the data in the class
• Ensure that properties or methods return a copy of any mutable data type that they return
• Your type should inherit only from another immutable type