Lesson 6: Composition over inheritance

This lesson practices Composition over inheritance at real C# application level. We start from design pain, study code, practice a small decision, predict behavior, and verify mastery.

Compose roles when inheritance starts describing “has-a” instead of “is-a”.

Composition over inheritance: Compose roles when inheritance starts describing “has-a” instead of “is-a”.
design pressure: A repeated change, duplication, or test pain that signals the model needs a better boundary.