in C#, when should we use abstract classes i...

In C#, abstract classes and interfaces with extension methods serve different purposes and are used in different scenarios. Here are some guidelines on when to use each:

Abstract Classes

Use abstract classes when:

1. You want to provide some default implementation for methods: Abstract classes can contain both abstract and non-abstract (concrete) methods. This allows you to provide some default behavior while still allowing derived classes to override specific methods.

2. You need to share state between methods: Abstract classes can have fields and properties that can be accessed and shared by all derived classes.

3. You want to restrict inheritance: You can mark an abstract class as sealed, preventing it from being inherited.

4. You need to provide constructor parameters: Abstract classes can have constructors, which is useful when you need to pass parameters to initialize the state of the class.

5. You want to provide static methods and constants: Abstract classes can have static methods and constants, which can be accessed without creating an instance of the class.

Interfaces with Extension Methods

Use interfaces with extension methods when:

1. **You want to add new functionality to existing types w...