public interface IPrintable
{
    void Print();
}





public class DocumentPrinter : IPrintable
{
    public void Print()
    {
        Console.WriteLine("Printing a document...");
    }
}

public class PhotoPrinter : IPrintable
{
    public void Print()
    {
        Console.WriteLine("Printing a photo...");
    }
}





class Program
{
    static void Main()
    {
        List printQueue = new List
        {
            new DocumentPrinter(),
            new PhotoPrinter()
        };

        foreach (var printable in printQueue)
        {
            printable.Print();
        }
    }
}