Sheridan wrote:

Do operations involving FileStream as input always return a MultiByteFileStream?

That is a well-known pattern, class cluster. A base class defining an interface and acting as a factory hiding the specific class returned. Cocoa uses that a lot, it results in a much cleaner architecture than that of .net and java. https://developer.apple.com/library/ios/documentation/General/Conceptual/Coc... Stephan