Design Patterns reference data
Software design patterns with descriptions and use cases.
Topic guide
What Design Patterns covers
Design-pattern reference data names the recurring solutions to recurring software-design problems: the creational, structural and behavioral patterns of the 'Gang of Four', the concurrency patterns that coordinate threads, the architectural patterns that shape whole systems, the SOLID principles behind them and the anti-patterns that come from misusing them. Patterns are vocabulary first and templates second: their value is that 'use a strategy here' conveys a design in four words. They also carry costs, since applying a pattern where a simple function would do adds indirection, so each entry states when to use it as well as what it is.
Key ideas
- Creational, structural, behavioral
- The three Gang of Four groups: patterns for creating objects, for composing them and for assigning responsibilities and communication.
- Coupling and cohesion
- Coupling is how much modules depend on one another; cohesion is how focused each module is. Good designs reduce the first and increase the second.
- Program to an interface
- Depend on abstractions rather than concrete classes so implementations can change without affecting callers.
- SOLID
- Five object-oriented principles: single responsibility, open/closed, Liskov substitution, interface segregation and dependency inversion.
- Composition over inheritance
- Build behavior by combining objects instead of extending class hierarchies, which keeps designs flexible.
- Anti-pattern
- A common response to a problem that looks reasonable but causes more trouble than it solves, such as the God Object.
- Architecture vs design pattern
- Architectural patterns (microservices, MVC) shape a whole system; design patterns (observer, factory) shape a few collaborating classes.
Common pitfalls
- Applying patterns by reflex. If a plain function or a simple class solves the problem, the pattern adds only complexity.
- Using Singleton as global state; it hides dependencies and makes testing harder.
- Treating the pattern's textbook structure as mandatory; adapt it to the language (closures can replace many pattern classes).
- Naming a pattern incorrectly; a decorator is not a proxy, even though both wrap an object.
Using it from an agent
- Name the pattern, state the problem it solves, show the minimal structure and note the main trade-off.
- Recommend the simplest design that works, and name the pattern only when it clarifies communication.
- Match the example to the user's language and idioms; functional languages often express these patterns with functions.
Start with: SOLID Principles · Creational Design Patterns
Datasets in Design Patterns
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Architectural Design Patterns
High-level structural patterns: MVC, MVVM, Microservices, Event-Driven, Layered, Hexagonal (Ports & Adapters), CQRS, Serverless, Service Mesh.
9 entries -
Behavioral Design Patterns
Patterns for communication between objects: Observer, Strategy, Command, Iterator, State, Template Method, Visitor, Mediator, Chain of Responsibility, Interpreter.
10 entries -
Concurrency Design Patterns
Patterns for multi-threaded programming: Producer-Consumer, Reader-Writer, Thread Pool, Future/Promise, Reactor, Monitor, Scheduler.
7 entries -
Creational Design Patterns
Patterns for object creation: Singleton, Factory Method, Abstract Factory, Builder, and Prototype with intents and use cases.
8 entries -
Reliable Background Job Patterns
Queue and worker design patterns for duplicate deliveries, failure recovery, concurrency, and bounded work.
10 entries -
SOLID Principles
Five design principles for writing maintainable object-oriented code.
12 entries -
Software Anti-Patterns & Design Pattern Misuse
Common software design anti-patterns, misuse of design patterns, code smells indicating trouble, and refactoring strategies to fix them.
8 entries -
Structural Design Patterns
Structural design patterns: Adapter, Bridge, Composite, Decorator, Facade, Flyweight, and Proxy with intents and when-to-use guidance.
7 entries
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