Abstract Factory

Intent

Create families of related objects without coupling clients to concrete classes.

Problem

Applications often need compatible product families such as light/dark UI components or provider-specific clients.

Solution

Expose a factory interface that creates a complete product family.

TypeScript Implementation

ThemeFactory creates matching buttons and checkboxes for light or dark themes.

npm run abstract-factory

Trade-offs

• Enforces product compatibility.
• Adding a new product type changes all factories.

Practical Perspective

Creational patterns are about controlling object creation so callers do not depend on concrete construction details.

For Abstract Factory, the important question is not “can I draw the UML diagram?” but “what dependency or decision becomes easier to change after I introduce this pattern?” In production code, the pattern should make ownership clearer, reduce accidental coupling, and give tests a natural seam.

Real-World Use Cases

• Framework integration points where Abstract Factory keeps responsibilities separated.
• Configuration-driven runtime behavior where Abstract Factory keeps responsibilities separated.
• Test fixture creation where Abstract Factory keeps responsibilities separated.
• Infrastructure objects whose setup should be centralized where Abstract Factory keeps responsibilities separated.

Decision Questions

• Who owns object creation?
• Which concrete type should callers be allowed to know?
• Can invalid combinations be prevented at construction time?
• Use it when products must be created as compatible families.
• Watch for factory interfaces growing too large as the product family expands.

Design Checklist

• Start with the client code: define the interface you want callers to depend on.
• Keep concrete classes small and named after one responsibility.
• Make creation, selection, delegation, or notification rules explicit instead of hidden in conditionals.
• Prefer composition roots for wiring objects together.
• Document the reason for using the pattern so future contributors do not cargo-cult it.

Common Mistakes

• Adding the pattern before the code has a real variation point.
• Creating abstractions that only rename concrete classes.
• Hiding important runtime behavior so debugging becomes harder.
• Letting examples stay toy-sized without showing where the pattern boundary sits in real code.
• Forgetting tests for negative paths, invalid states, or fallback behavior.

Testing Guidance

• Test through the public abstraction, not private implementation details.
• Use fakes or test doubles for collaborators so the pattern seam is verified.
• Add one integration-style test proving the objects are wired correctly.
• Cover edge cases that motivated the pattern: missing strategy, rejected state transition, failed handler, invalid factory family, stale proxy cache, or similar.
• Keep tests named after behavior and business outcome rather than pattern terminology.

Refactoring Signals

• The pattern is useful when adding a new variation no longer requires editing stable caller code.
• It is probably overdesigned when every new class has only one trivial method and no independent reason to exist.
• If contributors cannot explain the runtime flow quickly, simplify the wiring or improve names.
• If tests must mock too many layers, the abstraction boundary is likely in the wrong place.