Design Pattern Selector

Name: Design Pattern Selector
Author: BookForge

Select the right GoF design pattern for a specific object-oriented design problem. Use when facing any of these situations: object creation inflexibility (too many concrete class references), tight coupling between classes, subclass explosion from trying to extend behavior, inability to modify a class you don't own, need to vary an algorithm or behavior at runtime, want to add operations to a stable class hierarchy without modifying it, need to decouple a sender from its receivers, need undo/redo or event notification, or any time someone asks "which design pattern should I use?", "is there a pattern for this?", or "how do I design this more flexibly?" Analyzes the problem through 6 complementary selection approaches — intent scanning, purpose/scope classification, variability analysis, redesign cause diagnosis, pattern relationship navigation, and category comparison — to produce a scored pattern recommendation with trade-off analysis.

Install

1. Add marketplace

› /plugin marketplace add bookforge-ai/bookforge-skills

2. Install plugin

› /plugin install design-patterns-gof@bookforge-skills

3. Use the skill

› /design-pattern-selector

CC-BY-SA · Open sourceGitHub

Source Book

Design Patterns

Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides

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Implement the Abstract Factory pattern to create families of related objects without specifying their concrete classes. Use when a system must be independent of how its products are created, when it must work with multiple product families, when products are designed to be used together and you need to enforce that constraint, or when providing a class library revealing only interfaces. Covers factory-as-singleton, prototype-based factories, and extensible factory interfaces.

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Choose the right behavioral design pattern from the 11 GoF behavioral patterns. Use when someone asks "how do I make this algorithm swappable?", "should I use Strategy or State?", "how do I decouple senders from receivers?", "what's the difference between Observer and Mediator?", "how do I add undo/redo?", "how do I traverse a collection without exposing its internals?", or "how do I add operations to classes I can't modify?" Also use when you see switch statements selecting between algorithms, tightly coupled event handlers, objects that change behavior based on state, or request-handling logic that should be distributed across a chain. Analyzes via two taxonomies — what aspect to encapsulate as an object (algorithm, state, protocol, traversal) and how to decouple senders from receivers (Command, Observer, Mediator, Chain of Responsibility) — with explicit trade-offs for each choice.

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Bridge Pattern Implementor

Implement the Bridge pattern to decouple an abstraction from its implementation so both can vary independently. Use when you want to avoid a permanent binding between abstraction and implementation, when both abstractions and implementations should be extensible by subclassing, when implementation changes should not require recompiling clients, or when you need to share an implementation among multiple objects. Includes the evaluate-extremes design process (union vs intersection of functionality) and Abstract Factory integration for runtime implementation selection.

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Command Pattern Implementor

Implement the Command pattern to encapsulate requests as objects, enabling parameterized operations, queuing, logging, and undo/redo. Use when you need to decouple UI elements from operations, implement multi-level undo with command history, support macro recording, queue or schedule requests, or log operations for crash recovery. Includes the complete undo/redo algorithm using a command history list with present-line pointer, MacroCommand for composite operations, and SimpleCommand template for eliminating subclasses.