properlyextends

Properlyextends is a term used in object-oriented software design to describe the disciplined practice of extending classes or components in a way that preserves the base type’s contract, behavior, and invariants while enabling additional functionality. The goal is to avoid introducing brittleness or subtle regressions when subclassing or inheriting.

Key principles of properlyextending include honoring the Liskov Substitution Principle, so a subclass can replace its base type without altering expected outcomes. It also aligns with the Open/Closed Principle, encouraging extension rather than modification of existing code. Practitioners strive to keep public method contracts stable, ensure constructor and resource-management patterns are correctly chained with super calls when applicable, and minimize changes to the base class’s observable behavior.

Common techniques involve defining clear extension points through abstract or base classes, using protected hooks or the Template Method pattern, and providing interfaces that encapsulate behavior. Dependency injection and composition are often preferred to deep inheritance when possible, reducing tight coupling. When inheritance is used, new state should be encapsulated, and added features should not violate existing invariants or rely on fragile implementation details of the base class.

Pitfalls to avoid include overriding methods in ways that change their public contracts, introducing new side effects that affect existing clients, and leaking implementation specifics of the base class into subclasses. Documentation of extension points and expected guarantees helps maintainability and future compatibility.

Related concepts include inheritance, the Open/Closed Principle, the Liskov Substitution Principle, composition over inheritance, and abstraction strategies. Properlyextends thus represents a set of best practices intended to make class hierarchies safer, more maintainable, and easier to evolve.