In essence, the Liskov Substitution Principle promotes building a robust software ecosystem where interchangeable parts work seamlessly together, ensuring smooth operation and reliable functionality.
How LSP works
Subtypes inherit the supertype’s contract. They inherit the supertype’s methods and properties, ensuring compatibility with existing code.
Subtypes preconditions must be weaker or equal. The subtypes’ methods can have weaker preconditions (accepting more input types) than the supertype, but not stricter ones.
Subtypes postconditions must be stronger or equal. The subtypes’ methods can have stronger postconditions (guaranteeing more output guarantees) than the supertype, but not weaker ones.
Subtypes exceptions must be the same or subclasses of the supertype’s exceptions. The subtypes’ methods can throw only the same exceptions or subclasses of the exceptions thrown by the supertype.
Benefits
Improved code reuse Subtypes can leverage existing supertype code, reducing duplication and effort.
Enhanced flexibility You can easily replace objects with different subtypes without rewriting the program.
Increased reliability Substitutability guarantees program correctness even with changing types.
Reduced testing effort Tests for the supertype can often apply to conforming subtypes.
Remember
Use LSP when you have inheritance hierarchies and want to ensure type safety and program correctness.
Overuse can lead to unnecessary complexity and overly restrictive subtype definitions.
Design clear and concise contracts for both supertype and subtypes for efficient substitutability.