Design Patterns and Real-World Use Cases

🔍 When to apply design patterns? Design patterns provide proven solutions to common problems, improving maintainability, scalability, and clarity across your .NET codebase.

🏗️ Creational Patterns

These patterns deal with object creation mechanisms, optimizing flexibility and reuse.

📌 Singleton 🏷️ Ensures a single, global instance. Use-case: Centralized logging or configuration service.

📌 Factory Method 🏭 Defines an interface for creating objects, letting subclasses decide which class to instantiate. Use-case: Generating different notification types (email, SMS).

📌 Abstract Factory 🏺 Groups related factory methods without specifying concrete classes. Use-case: UI theme factories that produce consistent sets of components.

📌 Builder 🏗️ Separates object construction from its representation. Use-case: Step-by-step creation of complex reports or documents.

📌 Prototype 🌀 Creates new objects by copying an existing instance. Use-case: Duplicating a complex settings object with minimal overhead.

🛠️ Structural Patterns

These patterns ease the composition of classes and objects to form larger structures.

📌 Adapter 🔌 Allows incompatible interfaces to work together. Use-case: Wrapping legacy APIs to fit a modern interface.

📌 Bridge 🌉 Decouples an abstraction from its implementation. Use-case: Separating UI controls from rendering engines.

📌 Composite 🌳 Treats individual objects and compositions uniformly. Use-case: Building tree-like menu or file system hierarchies.

📌 Decorator 🎀 Adds responsibilities to objects dynamically. Use-case: Enhancing I/O streams with compression or encryption.

📌 Facade 🛡️ Provides a simplified interface to a complex subsystem. Use-case: Single entry point for database, caching, and messaging layers.

📌 Flyweight 🪶 Shares common state among many fine-grained objects to save memory. Use-case: Rendering thousands of similar graphical elements.

📌 Proxy 🪞 Provides a surrogate or placeholder for another object. Use-case: Lazy loading of large images or remote service calls.

🎭 Behavioral Patterns

These patterns focus on communication between objects and responsibility assignment.

📌 Chain of Responsibility 🔗 Passes a request along a chain until handled. Use-case: Multi-level logging or validation pipelines.

📌 Command 🎛️ Encapsulates a request as an object, allowing parameterization and queuing. Use-case: Undo/redo operations in an editor.

📌 Interpreter 📜 Defines a representation for a grammar and an interpreter to process sentences. Use-case: Parsing and evaluating simple scripting languages.

📌 Iterator 🔄 Provides sequential access without exposing underlying structure. Use-case: Navigating elements of a custom collection.

📌 Mediator 🗨️ Centralizes complex communication between related objects. Use-case: Chat room or UI event coordination.

📌 Memento 📝 Captures and restores an object’s internal state without violating encapsulation. Use-case: Snapshotting game state for checkpoints.

📌 Observer 👀 Defines a one-to-many dependency so observers update automatically. Use-case: UI data binding or real-time notifications.

📌 State 🎭 Allows an object to change behavior when its internal state changes. Use-case: Workflow engines or document lifecycle management.

📌 Strategy 🧠 Encapsulates interchangeable algorithms behind a common interface. Use-case: Swapping sorting or payment processing methods at runtime.

📌 Template Method 📐 Defines the skeleton of an algorithm, deferring steps to subclasses. Use-case: Standardizing file parsing with customizable steps.

📌 Visitor 🧳 Separates operations from the object structure on which they operate. Use-case: Applying analytics or reporting across a complex object graph.

💡 Choosing the right pattern:

• Create objects flexibly? → Creational (Singleton, Factory, Abstract Factory, Builder, Prototype)
• Build complex structures? → Structural (Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy)
• Manage object interactions? → Behavioral (Chain, Command, Interpreter, Iterator, Mediator, Memento, Observer, State, Strategy, Template, Visitor)

🏗️ Creational Patterns

These patterns deal with object creation mechanisms, optimizing flexibility and reuse.

📌 Singleton 🏷️ Ensures a single, global instance. Use-case: Centralized logging or configuration service.

📌 Factory Method 🏭 Defines an interface for creating objects, letting subclasses decide which class to instantiate. Use-case: Generating different notification types (email, SMS).

📌 Abstract Factory 🏺 Groups related factory methods without specifying concrete classes. Use-case: UI theme factories that produce consistent sets of components.

📌 Builder 🏗️ Separates object construction from its representation. Use-case: Step-by-step creation of complex reports or documents.

📌 Prototype 🌀 Creates new objects by copying an existing instance. Use-case: Duplicating a complex settings object with minimal overhead.

🛠️ Structural Patterns

These patterns ease the composition of classes and objects to form larger structures.

📌 Adapter 🔌 Allows incompatible interfaces to work together. Use-case: Wrapping legacy APIs to fit a modern interface.

📌 Bridge 🌉 Decouples an abstraction from its implementation. Use-case: Separating UI controls from rendering engines.

📌 Composite 🌳 Treats individual objects and compositions uniformly. Use-case: Building tree-like menu or file system hierarchies.

📌 Decorator 🎀 Adds responsibilities to objects dynamically. Use-case: Enhancing I/O streams with compression or encryption.

📌 Facade 🛡️ Provides a simplified interface to a complex subsystem. Use-case: Single entry point for database, caching, and messaging layers.

📌 Flyweight 🪶 Shares common state among many fine-grained objects to save memory. Use-case: Rendering thousands of similar graphical elements.

📌 Proxy 🪞 Provides a surrogate or placeholder for another object. Use-case: Lazy loading of large images or remote service calls.

🎭 Behavioral Patterns

These patterns focus on communication between objects and responsibility assignment.

📌 Chain of Responsibility 🔗 Passes a request along a chain until handled. Use-case: Multi-level logging or validation pipelines.

📌 Command 🎛️ Encapsulates a request as an object, allowing parameterization and queuing. Use-case: Undo/redo operations in an editor.

📌 Interpreter 📜 Defines a representation for a grammar and an interpreter to process sentences. Use-case: Parsing and evaluating simple scripting languages.

📌 Iterator 🔄 Provides sequential access without exposing underlying structure. Use-case: Navigating elements of a custom collection.

📌 Mediator 🗨️ Centralizes complex communication between related objects. Use-case: Chat room or UI event coordination.

📌 Memento 📝 Captures and restores an object’s internal state without violating encapsulation. Use-case: Snapshotting game state for checkpoints.

📌 Observer 👀 Defines a one-to-many dependency so observers update automatically. Use-case: UI data binding or real-time notifications.

📌 State 🎭 Allows an object to change behavior when its internal state changes. Use-case: Workflow engines or document lifecycle management.

📌 Strategy 🧠 Encapsulates interchangeable algorithms behind a common interface. Use-case: Swapping sorting or payment processing methods at runtime.

📌 Template Method 📐 Defines the skeleton of an algorithm, deferring steps to subclasses. Use-case: Standardizing file parsing with customizable steps.

📌 Visitor 🧳 Separates operations from the object structure on which they operate. Use-case: Applying analytics or reporting across a complex object graph.

💡 Choosing the right pattern:

• Create objects flexibly? → Creational (Singleton, Factory, Abstract Factory, Builder, Prototype)
• Build complex structures? → Structural (Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy)
• Manage object interactions? → Behavioral (Chain, Command, Interpreter, Iterator, Mediator, Memento, Observer, State, Strategy, Template, Visitor)