static void Main() { StreamUser someStreamUser = new StreamUser(); MemoryStream testMemoryStream = new MemoryStream(new byte[] { }); using (FileStream testFileStream = new FileStream("test.dat", FileMode.OpenOrCreate)) { // Cannot be used with testMemoryStream. someStreamUser.ManipulateFileStream(testFileStream); someStreamUser.ManipulateAnyStream(testFileStream); someStreamUser.ManipulateAnyStream(testMemoryStream); } }