public static void PrintAll(this PrintApp.Printer printer, params string[] msgArr)
{
for (int i = 0; i < msgArr.Length; i++)
{
printer.Print(msgArr[i]);
}
}
static void Main(string[] args)
{
Printer printer = new Printer();
Printer colPrinter = new ColourPrinter();
Printer photoPrinter = new PhotoPrinter();
// virtual methods are called
printer.Print("message");
colPrinter.Print("message");
photoPrinter.Print("message");
// specialised methods
(colPrinter as ColourPrinter).Print("message", ConsoleColor.Blue);
(photoPrinter as PhotoPrinter).Print(new Photo());
Console.ReadKey();
}