Liskov Substitution Principle in C# with Example

The page explains the Liskov Substitution Principle as a rule of object-oriented design in which objects should be replaceable with subtype instances without breaking program correctness. It uses a Bird and Ostrich example to show how an overridden Fly method that throws an exception breaks substitution.

Reading notes

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• LSP is presented as one of the five SOLID principles.
• A subtype should be usable wherever the base type is expected without changing the program’s correctness.
• In the first example, Bird defines Fly and Ostrich overrides Fly to throw NotSupportedException.
• Assigning an Ostrich to a Bird reference and calling Fly causes an exception.
• The text treats that exception as a violation of LSP because the derived class changes the expected behavior.
• To follow LSP, the page suggests a better hierarchy or interfaces for different behaviors.
• It introduces IBird with a Move method as the shared contract.
• FlyingBird implements IBird and calls Fly from Move.
• Ostrich implements IBird and calls Run from Move.
• In the refactored code, both FlyingBird and Ostrich can be used through IBird without breaking the program.
• The page concludes that this design makes the code more robust, maintainable, and scalable.