C# in Depth

Extension method syntax259extension method—just add the this keyword. Listing 10.3 shows the same class as inlisting 10.1, but this time with both methods as extension methods.Listing 10.3The StreamUtil class again, but this time with extension methodspublic static class StreamUtil{const int BufferSize = 8192;}public static void CopyTo(this Stream input,Stream output){byte[] buffer = new byte[BufferSize];int read;while ((read = input.Read(buffer, 0, buffer.Length)) > 0){output.Write(buffer, 0, read);}}public static byte[] ReadFully(this Stream input){using (MemoryStream tempStream = new MemoryStream()){CopyTo(input, tempStream);return tempStream.ToArray();}}Yes, the only big change in listing 10.3 is the addition of the two modifiers, as shown inbold. I’ve also changed the name of the method from Copy to CopyTo. As we’ll see in aminute, that will allow calling code to read more naturally, although it does lookslightly strange in the ReadFully method at the moment.Now, it’s not much use having extension methods if we can’t use them…10.2.2 Calling extension methodsI’ve mentioned it in passing, but we haven’t yet seen what an extension method actuallydoes. Simply put, it pretends to be an instance method of another type—the typeof the first parameter of the method.The transformation of our example code that uses StreamUtil is as simple as thetransformation of the utility class itself. This time, instead of adding something inwe’ll take it away. Listing 10.4 is a repeat performance of listing 10.2, but using the“new” syntax to call CopyTo. I say “new,” but it’s really not new at all—it’s the same syntaxwe’ve always used for calling instance methods.Listing 10.4Copying a stream using an extension methodWebRequest request = WebRequest.Create("http://manning.com");using (WebResponse response = request.GetResponse())using (Stream responseStream = response.GetResponseStream())Licensed to Rhona Hadida