What is the Difference Between Classes vs Protocols

Question

I'm going through the docs because I am about to implement a protocol instead of a class (something I've never done before), and I'm curious as to the difference between the two.

Can someone give an example in plain words?

Thanks

Answer 1

A class serves as a blueprint for creating one or more objects based on specific implementation of that class. A good analogy is a form for cutting out butter-cookies. The form‘s attributes (shape, size, height) define the cookies that you can cut out with it. You have only one form (class) but you can create many cookies (instances of that class, ie. objects) with it. All cookies are based on that particular form. Similarily all objects that are instances of that class are identical in their attributes.

Classes = data and methods (special functions), all sophistically bundled together.

Classes define, what their inner content (data) is + what kind of work (methods) they can do. The content is based on variables that hold various number types, strings, constants, and other more sophisiticated content + methods which are chunks of code that (when executed) perform some computational operations with various data.

All methods defined in class have their Definition - that defines the name of the method + what (if any) data the methods takes in for processing and what (if any) data the methods spits out for processing by someone else. All methods defined in class also have Implementation – the actual code that provides the processing – it is the innerworkings of methods.. inside there is code that processes the data and also that is able to ask other methods for subprocessing data. So the class is a very noble type in programming.

If you understand the above, you will understand what a protocol is.

A protocol is a set of one or more method declarations and that set has a name and represents a protocol. I say declarations, because the methods that together are defined by a particular protocol, do not have any implementation code defined.. The only thing that exist is their names declared. Look above - in class, you have always defined not only what methods the class has, but also how that work will be done. But methods in protocol do not have any implementation.

Lets have a real life analogy again, it helps. If you come to my house to live here for a week, you will need to adhere to my TidyUp protocol. The TidyUp protocol defines three methods - wash the dishes every day, clean the room, and ventilate fresh air. These three methods, I define them..are something you will do. But I absolutely do not care, how the implementation should look like, I just nominaly define the methods. You will implement them, ie.you define how the details of that work (those methods) will look like. I just say, adhere to my protocol and implement it as you see fit.

Finale – You can declare some class. You can separately also declare a protocol. And you can then declare, that this class, in addition to its own methods, will adopt or adhere to that protocol, ie. the class wil implement the protocol’s methods.