What are pros and cons of Singleton?

Pros of Singleton Design Pattern

Ensures a Single Instance

• Guarantees that a class has only one instance throughout the application.
• Prevents duplicate instances that could cause inconsistent behavior.

Global Access

• Provides a single, well-known access point to the instance.
• Simplifies access to shared resources, like configuration settings or loggers.

Lazy Initialization

• Allows the instance to be created only when it is needed, which can save resources in some cases.

Resource Management

• Useful for managing shared resources, such as database connections or thread pools.
• Especially if the resource is expensive to initialize or manage, such as database connections or logging systems.
• In multi-threaded environments, creating and managing multiple instances of a resource can lead to race conditions or deadlocks.
• Shared resources often need to maintain a single state accessible to all parts of the application (e.g., configuration settings or a cache).
• Multiple instances can make cleanup and resource deallocation complex, potentially leading to resource leaks.

Cons of Singleton Design Pattern

Tight Coupling

• Classes that depend on the Singleton are tightly coupled to it, reducing flexibility and making the code harder to refactor or extend.

Testing Challenges

• Hard to test since Singletons persist across tests unless explicitly reset.
• Mocking or overriding Singletons during tests requires additional effort.

Memory Retention

• Since the Singleton instance persists throughout the application's lifecycle, it can lead to memory leaks or excessive resource usage if not properly managed.

Breaks Single Responsibility Principle (SRP)

• Combines instance management responsibilities with its primary role, violating SRP and making the class less modular.

Hidden Dependencies

• Dependencies on the Singleton are implicit, making the code harder to read, maintain, and refactor.