Design Patterns Applied
Named solutions to recurring problems - on real code.
Design patterns as a shared vocabulary, taught on the messy ledger codebase rather than toy examples: factory and builder for creation, strategy and template method for behavior, adapter and facade to tame legacy and third-party code, decorator and composite for structure, observer for events - and, crucially, when a pattern is the wrong call.
Lessons in this stage
- 01
Patterns as Vocabulary
IntermediateWhat a design pattern really is - a named, reusable solution to a recurring problem - the Gang of Four categories, and the pattern-fever trap of forcing them where they don't fit.
13 min - 02
Factory & Builder
IntermediateCreational patterns: factory method and abstract factory to centralize object creation, and the builder for constructing complex objects (a Report, a Transaction) step by step.
15 min - 03
Strategy & Template Method
AdvancedBehavioral patterns: strategy formalizes the interchangeable fee policies from Open/Closed; template method fixes an algorithm's skeleton while letting steps vary.
15 min - 04
Adapter & Facade
IntermediateStructural patterns for taming legacy and third-party code: adapter makes an incompatible interface fit, facade puts a simple front on the messy LedgerManager subsystem.
14 min - 05
Decorator & Composite
AdvancedDecorator layers behavior (logging, caching, extra fees) without subclass explosion; composite treats a tree of account groups and single accounts uniformly.
15 min - 06
Observer & When Patterns Hurt
AdvancedObserver decouples an audit/event publisher from its subscribers (a preview of domain events) - and an honest lesson on over-engineering: when a pattern adds cost without benefit.
14 min