委托返回类型的协变性

    class Program
    {
        static void Main(string[] args)
        {
            StreamFactory factory = GenerateSampleData;//(3)
            using (Stream stream = factory())//(4)
            {
                int data;
                while ((data=stream.ReadByte())!=-1)
                {
                    Console.WriteLine(data);
                }
            }
            Console.Read();
        }

        private delegate Stream StreamFactory();//(1)

        static MemoryStream GenerateSampleData()//(2)
        {
            byte[] buffer = new byte[16];
            for (int i = 0; i < buffer.Length; i++)
            {
                buffer[i] = (byte)i;
            }
            return new MemoryStream(buffer);
        }
    }