Favor composition over inheritance principle
The Favor Composition over Inheritance Principle recommends composing objects rather than inheriting from classes when composition provides a more flexible, maintainable, and less coupled design.
Object-Oriented Software Design in C++
The Favor Composition over Inheritance Principle recommends using composition instead of inheritance when composition provides more flexible, encapsulated, less complex, and loosely coupled designs.
- How it is used
- Uses composition to choose between is-a and has-a relationships when subclass inheritance would hardcode object behavior.
- How deep it goes
- Explains tradeoffs through flawed and refactored toy designs, stopping short of broader implementation or ownership guidance.
- Examples
- Demonstrates Toy objects composed with PlayAction and Sound behaviors, including runtime replacement of a train’s sound.
- What you can do after
- Apply composition in C++ class designs to share, delegate, assign, and modify object behaviors at run time.
Software Design for Python Programmers
The Favor Composition over Inheritance Principle recommends using composition instead of inheritance when composition provides a more flexible and maintainable design.
- How it is used
- Guides choosing has-a relationships over inheritance when behavior must remain flexible and changeable at runtime.
- How deep it goes
- Demonstrates composition through concrete Python classes, delegation, constructor injection, setters, and runtime behavior changes.
- Examples
- Uses toys with interchangeable play and sound behaviors, including a train whose sound changes after creation.
- What you can do after
- Apply it by composing Python objects whose behaviors can be assigned, shared, delegated, and modified at runtime.
Related concepts
- inheritancecontrasts with · Inheritance is a mechanism by which a child type or element receives properties, values, or behavior from a parent, subject to system rules and possible overrides.
- principlekind of · A principle is a general rule, guideline, or value that guides decisions, behavior, or judgments.
- flexibilityuses · Flexibility is the capacity of a system, design, or process to adapt to changing requirements or conditions without extensive restructuring.
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