Refactoring into a Model - Extra Credit Questions

If you are creating a instance variable to use directly like you seem to be doing in the example it makes no difference, but iOS best practices is not to underscore the "instance variable". It use to be good practice to assign underscores to property names so you could tell them apart from the instance variable, for example: predictions = _predictions; but that is not really common either as most people use self.property to access properties. The underscore in properties is still used it is just happening under the hood for you. Again for your question I have heard that Apple themselves specifically says not to underscore instance variables, but you will still see people doing it as a habit from other languages mostly. There are Objective-C coding convention best practices guides that are all different in some ways so it is a debate that continues.