Topic 9. Generic programming: generic classes and functions, variance, reified parameters

Goal: learn to design generic types, specify sufficient constraints, distinguish producers from consumers, and verify both the behavior and the static contract of your own API.

Lecture contents

1. Type parameters and generic classes — A type parameter as part of the contract · Example 1. A stack on linked nodes
2. Generic functions and bounds — Generic functions and constraints · Nullable bounds and definitely non-null
3. Variance and projections — Invariance: why an element subtype is not enough · Declaration-site variance · Use-site projections
4. Type erasure and reified — Type erasure and reified · Sealed results, Nothing, and aliases
5. API design and testing — API design: from operations to variance · Verifying contracts without unchecked casts · Generalization and domain identity

Practice and review

• Practice — 3 worked examples with complete code
• Tasks — 30 variants, each with tasks at three difficulty levels
• Summary — conclusions, self-check questions, and useful links