What does prefer composition over inheritance mean, and can you show a case where composition produces a cleaner C# design?

Composition over inheritance in practical C#

Combines focused collaborators for independent behavior while recognizing cases where a genuine stable hierarchy remains simpler.

1Say itAnswer out loud first

2CompareCompare with Core answer

3RefineRefine with Stronger and Advanced

TL;DR

Preferring composition means building behavior from focused collaborators instead of inheriting mainly for code reuse. For a report exporter, I might compose an IReportFormatter, IStorageWriter, and INotificationSender instead of creating PdfEmailExporter, PdfBlobExporter, CsvEmailExporter, and more subclasses. The coordinator owns the workflow while each collaborator owns one variation. Dependencies are explicit and each part can be tested through its contract.

Full answer below

Practice focus

Object collaboration, strategies, decorators, independent variation, delegation, testability, and valid inheritance use cases.

Answer first

Answer path

Core answer first, then checkpoints toward a stronger answer.

Start
Core answer
Start here. This is the direct spoken answer to practice first.
Why this question matters
Composition builds behavior by giving an object focused collaborators and delegating work to them. It is often safer than inheritance because each behavior can vary without exposing base-class internals or creating subclass combinations.
Preferring composition means building behavior from focused collaborators instead of inheriting mainly for code reuse. For a report exporter, I might compose an IReportFormatter, IStorageWriter, and INotificationSender instead of creating PdfEmailExporter, PdfBlobExporter, CsvEmailExporter, and more subclasses. The coordinator owns the workflow while each collaborator owns one variation. Dependencies are explicit and each part can be tested through its contract.
Checkpoint
Stronger answer
Optional upgrade with examples, trade-offs, and sharper phrasing.
Composition has a cost: more objects, wiring, and contracts can obscure a simple algorithm if used mechanically. I keep collaborators cohesive and avoid one interface per three lines. Inheritance remains reasonable when there is a stable is-a relationship, shared invariant, and template behavior designed for extension. The preference means composition is the safer default for code reuse, not that inheritance is forbidden.

Review signals

Use these to catch weak phrasing, shallow reasoning, and risky claims.

Common mistakesCandidateCommon mistakesMistakes that weaken the answer or signal shallow understanding.Open details

Details

Saying inheritance should never be used.
Creating a collaborator for every tiny method.
Building an unreadable dependency graph.
Ignoring decorator or policy execution order.

What does prefer composition over inheritance mean, and can you show a case where composition produces a cleaner C# design?

Practice focus

Answer path

Why this question matters

Review signals

Follow-up prompts

Continue the section

Tech stacks

Skill areas

Suggest an improvement