What are the most common design patterns you use in OOP?

One of the earliest patterns that I came across in the beginning of my career journey is the Singleton pattern. I've seen this getting extensively used for logging, database connections etc. It is the most memory efficient in terms of the number of instances created. There are multiple ways a singleton can be initialised(eager vs lazy) and also make it thread safe(synchronised getInstance method vs synchronised block).

Before diving: Please try to focus problem itself, rather than patterns. Pattern selection is a third phase of the development process: 1) Try to handle the problem. It doesn't matter if you're using best practices or not, but first focus on resolving the problem. 2) Try to get a better solution using best practices 3) Apply patterns If you want to know which of them to use the answer will be "it depends ". If you have a complex object creation process and it has steps to create it, then use Builder. If you want to know which pattern is suitable for "real object-oriented programming" then learn Decorator. Factory group of patterns allow you to encapsulate the object itself, providing its consuming via contracts

Among creational patterns, the ones I use most frequently are the Abstract Factory and Factory Method. They help avoid creating dependencies inside classes. I would only use the Singleton pattern as a public object provided by a framework if I want to restrict control of its lifecycle. Otherwise, Singleton can introduce quite a lot of obscure dependencies into your codebase and make it rigid.

Btw The flyweight pattern is used in .NET by CLR to create objects and instances. When you create an instance of a class, it creates only one object but will create multiple instances. If you have a contract-oriented design and you want other/external services to be in the "same line as yours" then use Adapter. Decorator as I mentioned, is my favorite and one of the real cool pattern to be used in OOP world.Because every object consist from multiple smaller objects and real object creation relies on Decorator.

Understand the Singleton pattern and its role in ensuring only one instance of a class exists in a program. Delve into best practices for implementation, ensuring global access and discussing crucial use cases for maintaining control and consistency.

Adapter and Decorator are instrumental when you are following the SOLID principles and using Dependency Injection properly. These two patterns are among the most powerful tools that facilitate the actual reuse of existing classes. Thanks to the Adapter and Decorator, your codebase can become truly composable.

Dive into the Builder pattern, separating the construction of complex objects from their representation. Follow a step-by-step guide for implementation, highlighting its benefits in creating objects with different configurations while maintaining readability and flexibility.

The most common pattern in iOS development (especially in UIKit) is Delegation Pattern. In delegation, an object handles a request by delegating to a second object (the delegate) through the delegation protocol. By relying on a delegate protocol instead of a concrete object, the implementation is much more flexible: any object that implements the protocol can be used as the delegate. Use this pattern to break up large classes or create generic, reusable components.

Explore the purpose of the Factory Method pattern in Object-Oriented Design, allowing subclasses to determine the class instantiation dynamically. Learn its implementation and real-world use cases for enhanced flexibility.