2. Factory Method and Simple Factory

public interface INotification { void Send(string to, string msg); }
public class EmailNotification : INotification { public void Send(string to, string msg) { } }
public class SmsNotification : INotification { public void Send(string to, string msg) { } }

// Simple factory
public static class NotificationFactory
{
    public static INotification Create(string channel) => channel switch
    {
        "email" => new EmailNotification(),
        "sms" => new SmsNotification(),
        _ => throw new ArgumentException($"Unknown channel {channel}")
    };
}

// GoF Factory Method: subclasses decide what to create
public abstract class DocumentExporter
{
    protected abstract IWriter CreateWriter();          // factory method
    public void Export(Doc d) { var w = CreateWriter(); w.Write(d); }
}
public class PdfExporter : DocumentExporter { protected override IWriter CreateWriter() => new PdfWriter(); }