NullObject.md

Null Object

Note A behavioral design pattern with no behaviors 🙂

A no-op object that conforms to the required interface, satisfying a dependency requirement of some other object.

Intent

Important Intent The Null Object pattern encapsulates the absence of an object by providing a substitutable alternative that offers do nothing behavior.

Explanation

The Null Object design pattern provides a default object that does nothing in place of a null reference, preventing null reference exceptions. It defines an abstract interface for a certain task, and if there's no data to be processed, instead of using a null reference, a null object implementing this interface is used. This reduces the need for null checking and improves code readability and robustness.

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Motivation to use

• When component A uses component B, it typically assumes that B is non-null
  • You inject B, not B? or some Option<B>
  • You do not check for null (?.) on every call
• There is no option of telling A not to use an instance of B
  • Its use is hard-coded
• Thus, we build a no-op, non-functioning inheritor of B and pass it into A

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Summary from the course

• Implement the required interface
• Rewrite the methods with empty bodies
  • If method is non-void, return default(T)
  • If these values are ever used, you are in trouble
• Supply an instance of Null Object in place of actual object
• Dynamic construction possible
  • With associated performance implications

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