What are the key differences between creational and structural design patterns?

1 Creational Patterns

Creational design patterns abstract the instantiation process. They help make a system independent of how its objects are created, composed, and represented. Patterns like Singleton, Factory Method, Abstract Factory, Builder, and Prototype fall under this category. Each of these patterns solves a specific problem related to object creation. For example, the Singleton pattern ensures that a class has only one instance and provides a global point of access to it, which is particularly useful when managing a connection to a database or a file system.

2 Structural Patterns

Structural design patterns ease the design by identifying a simple way to realize relationships between entities. They focus on how classes and objects are composed to form larger structures while keeping these structures flexible and efficient. Common structural patterns include Adapter, Bridge, Composite, Decorator, Facade, Flyweight, and Proxy. Each of these serves a different purpose; for example, the Adapter pattern allows incompatible interfaces to work together, while the Facade pattern provides a simplified interface to a complex subsystem.

3 Object Creation

In creational patterns, the emphasis is on the flexibility and reusability of the object creation process. These patterns provide mechanisms for creating objects that increase flexibility and reuse of existing code. For instance, the Factory Method pattern allows a class to defer instantiation to subclasses, and the Prototype pattern allows you to copy or clone existing objects instead of creating new ones, which can be more efficient.

4 Composition Over Inheritance

Structural patterns often prefer composition over inheritance. Rather than establishing relationships through inheritance, these patterns achieve flexibility by composing objects to perform new functionalities. This approach provides a more modular and easier to change structure. For example, the Composite pattern allows you to compose objects into tree structures to represent part-whole hierarchies, enabling clients to treat individual objects and compositions uniformly.

5 Flexibility in Design

The flexibility in your software's design can be significantly enhanced by appropriately using creational and structural patterns. Creational patterns provide the flexibility in how your objects are created and managed. On the other hand, structural patterns give you the flexibility in the way objects are composed and extended. Both sets of patterns allow for designs that are easier to understand, modify, and extend.

6 Independence and Encapsulation

Creational patterns tend to focus on creating objects in a manner that promotes independence and encapsulation. This is achieved by hiding the details of object creation and allowing for the introduction of new types of objects without changing existing code. Structural patterns, conversely, focus on establishing robust interfaces that can evolve without compromising the overall system architecture.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?