What design patterns have you applied in your development practice?

In my C# development practice, I have applied several design patterns that help make the code more maintainable and extensible:

• Singleton — for creating a single instance of a class, for example, for a logger or configuration manager.
• Factory Method — for creating objects without tight coupling to specific classes, facilitating functionality extension.
• Repository — for abstracting data access, simplifying testing and changing data sources.
• Dependency Injection — for managing dependencies between classes, improving modularity and testability.

Example of using Singleton in C#:

public class Logger
{
    private static Logger _instance;
    private static readonly object _lock = new object();

    private Logger() { }

    public static Logger Instance
    {
        get
        {
            lock (_lock)
            {
                if (_instance == null)
                    _instance = new Logger();
                return _instance;
            }
        }
    }

    public void Log(string message)
    {
        Console.WriteLine(message);
    }
}

Using such patterns helps create flexible and easily maintainable applications.