freemo
d9e5668cec
Fixes and improvements from exhaustive audit: Consistency fixes in SKILL.md: - 'Pipe & Filter' → 'Pipe and Filter' (one stray '&' found and corrected) - 'Singleton for factory instance' → clarified to 'register factory as singleton-scoped via DI container' (less misleading wording) - Documentation Format section updated with note that SKILL.md itself is the authoritative source for related-pattern combinations Coverage fix — Related Patterns sections: - Added '## Related Patterns' to ALL 94 pattern files (was 0/94) - Each section lists 3–6 related patterns with relationship descriptions - Covers: why they're related, when to prefer one vs the other, and which are often confused SOLID principles → Creational → Structural → Behavioral → Architectural → Concurrency → Functional → Resilience → Data Access → Messaging → Testing → Error Handling → Microservice — all 13 categories covered Code verification: - Python: 0 failures (all 85 testable blocks pass) - Go: 0 failures (all 76 testable blocks pass) - JavaScript: 0 failures (all 78 testable blocks pass) - All 239 code blocks verified correct after edits Final skill state: - 108 files, 36,524 lines across 13 reference categories - 94/94 pattern files have Related Patterns sections - 2,815-line SKILL.md with 67 decision trees, 23 scenarios, 0 broken references, 0 naming inconsistencies
Creational Design Patterns
Creational patterns deal with object creation mechanisms — abstracting instantiation so that systems remain flexible about what gets created, who creates it, and how.
The 7 Creational Patterns
| Pattern | Intent | Complexity | Frequency |
|---|---|---|---|
| Factory Method | Defer instantiation to subclasses via a creator method | Low | Very High |
| Abstract Factory | Create families of related objects without concrete classes | Medium | High |
| Builder | Construct complex objects step-by-step with a fluent API | Medium | High |
| Prototype | Clone existing objects instead of building from scratch | Low | Medium |
| Singleton | Ensure exactly one instance exists globally | Low | High |
| Object Pool | Reuse expensive objects from a pre-allocated pool | Medium | Medium |
| Dependency Injection | Supply dependencies externally instead of creating them internally | Low | Very High |
When to Use Which
Need to create one of several related types at runtime?
--> Factory Method
Need to create families of related objects that must be consistent?
--> Abstract Factory
Need to construct a complex object with many optional parts?
--> Builder
Need to duplicate an existing configured object?
--> Prototype
Need exactly one shared instance (and DI is not an option)?
--> Singleton
Need to reuse expensive-to-create objects (connections, threads)?
--> Object Pool
Need to decouple a class from the specific implementations it uses?
--> Dependency Injection
Comparison Matrix
| Concern | Factory | Abstract Factory | Builder | Prototype | Singleton | Object Pool | DI |
|---|---|---|---|---|---|---|---|
| Hides concrete type | Yes | Yes | Partially | No | N/A | N/A | Yes |
| Supports families | No | Yes | No | No | No | No | Yes |
| Fluent API | No | No | Yes | No | No | No | No |
Avoids new |
Yes | Yes | Yes | Yes | No | Yes | Yes |
| Thread-safety concern | Low | Low | Low | Medium | High | High | Low |
| Testability | Good | Good | Good | Good | Poor | Good | Excellent |
Key Principle
Favor composition over inheritance, and injection over creation.
Most modern codebases rely heavily on Factory Method and Dependency Injection as their primary creational strategies. Use others when their specific strengths match a concrete problem.
Language Idioms
- Python: Factories are often plain functions; Singletons use
__new__or module-level instances; DI via constructor args. - Go: Factories are
NewXxx()functions; Singletons usesync.Once; no classes so Builder uses method chaining on structs. - JavaScript: Module exports naturally singleton; Factories return plain objects or class instances; Prototype via
Object.createor manual clone.