Lesson 9: Generics and variance

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

Use type parameters to express reusable, type-safe abstractions.

Generics and variance: Use type parameters to express reusable, type-safe abstractions.
design pressure: A repeated change, duplication, or test pain that signals the model needs a better boundary.