How can you ensure openness for extension and closedness for modification in software components?

The Open/Closed Principle from SOLID states that software entities should be open for extension but closed for modification. This is achieved through the use of abstractions and polymorphism.

In C#, this can be implemented via:

• Interfaces and abstract classes that define a contract.
• Inheritance and method overriding to extend functionality without changing existing code.
• Using design patterns, such as Strategy or Decorator, to add new behavior.

Example:

public abstract class Logger
{
    public abstract void Log(string message);
}

public class FileLogger : Logger
{
    public override void Log(string message)
    {
        // Logic to write to a file
    }
}

public class DatabaseLogger : Logger
{
    public override void Log(string message)
    {
        // Logic to write to a database
    }
}

// To add a new type of logger, there is no need to change existing classes, just create a new class inheriting Logger.