To abstract this code, we need a way to use a type as a parameter. Using extensions, we then make each of our character types conform to Initializable. And that's true we sometimes don't want to tell if the delegate is of value type or reference type . Thats everything for this article! To evaluate how good a move is, minimax uses a heuristic function to know how good the game state after such move. While protocol-oriented programming is a term that mostly refers to Swift, the concept is not new. WWDC 2015: Protocol-Oriented Programming in Swifthttps://developer.apple.com/videos/play/wwdc2015/408/, Introducing Protocol-Oriented Programming in Swift 3https://www.raywenderlich.com/814-introducing-protocol-oriented-programming-in-swift-3, The Swift Programming Language Swift 4.2 Declaration #Protocol Property Declarationhttps://docs.swift.org/swift-book/ReferenceManual/Declarations.html#ID370, The Swift Programming Language Swift 4.2 Protocolshttps://docs.swift.org/swift-book/LanguageGuide/Protocols.html#ID269, Apple Developer Documentation Collectionhttps://developer.apple.com/documentation/swift/collection, Apple Developer Documentation Equatablehttps://developer.apple.com/documentation/swift/equatable. The typical game AI algorithm is minimax, which is used in all sorts of adversarial games, e.g., chess. That's also reassuring because I wouldn't know where I introduced the cycle. Once the UI is implemented, you can play our little game against the AI. Most programming languages, including Swift, are object-oriented so this is the paradigm you pick first when you learn to program. So I prefer to adapt the algorithm to return not only the value of a move but also the move. Thanks to it, we can then create the makeCharacters(from:upTo:) generic function, using a CSwift generic with an Initializable type constraint. Notice also that maxHealth is back to being a static property. Two of its requirements are straightforward to implement: Here we can see another of the advantages of protocol-oriented programming which I did not discuss yet. So you will still have to use classes in your projects. I talk about recursion in-depth in my article on functional programming. Here we can see another couple of problems of inheritance. But I often recommend the opposite approach and start from concrete types, creating protocols only when needed. You are right, when run as a command line app, there's indeed no reference cycle. All an algorithm needs is a few protocol requirements. If we add new characters to our game and we forget to initialize any of these properties, the compiler will be okay with it. So, as a rule, dont make a protocol descend from another one unless you need it. These are usually healing spells. So the algorithm takes an extra depth parameter, which it decreases at each step. We need to know when a team member has performed its move for the current round. We now need to extract the available actions from each character. If you havent watched the presentation, I strongly recommend that you watch the video at least once. The official document from Apple defines a protocol as below. These are not stored properties like they were in our classes. I will only focus on what is relevant to understand protocol-oriented programming or this article would turn into a book. That creates another problem. know if a position is terminal, i.e., when a player wins, and the game is over; find a heuristic function to evaluate game states; find all the possible moves for a player (called. Unfortunately, I dont have a wizard icon. Trying to protect the object from unexpected changes by the instances, you will be defensive about coping the object. We can add conformance to any type, even to types that we dont own, whether they belong to the iOS SDK or a third-party framework. Click again to stop watching or visit your profile/homepage to manage your watched threads. Since clerics can also cast spells, we also want to share code between the Cleric and Witch classes. We still have no idea how we will implement these requirements for our Game type, but that does not matter. In Swift, you can add code to any type through extensions, even to types you dont own. We could use these types in all sorts of games with different rules. This makes it harder to break invariants because a protocol defines the appropriate access for each property. But thats only because we already did the abstraction work in the previous section. Only the destination of an attack needs to be a character. So, even if paradigms like protocol-oriented programming and functional programming can be useful, object-oriented programming is not going away. The game is played by two teams of five characters each (one will be controlled by a simple AI algorithm that we will implement later). The inheritance structure itself is not so flexible because of the following reasons. The protocol can then be adopted by a class, structure, or enumeration to provide an actual implementation of those requirements. We created the latter only when we needed to share code. In fact, its beneficial for common iOS development. The minimax algorithm uses the min(_:_:) and max(_:_:) functions, which in Swift only work on types that conform to Comparable. My proposal may be a short-cut workaround until Swift protocols can become what we expect and need. It will include many ideas that you can pick up even if you are not well-versed in iOS development. I continued experimenting and ended up with this: Which compiles and at first glance appears to do what I want. I agree with you that in most cases, using a weak reference to the delegate object is the correct way. One of the great features of protocols is that any Swift type can conform to them. Windows Insider Build 20161 Brings Redesigned Start Menu & More! SwiftUI slightly improves the situation. But our new character classes will inherit the meaningless values of Character, creating inconsistent states and strange bugs. So, the algorithm cannot always go all the way down to a victory position. Any type conforming to Character will get this computed property. All we would get runtime crashes, which we might not catch in our testing. To expose them, we will start modelling the characters for our game using classes. First I thought of adding a protocol extension with a default implementation: This would probably work if I did not have the BaseDataProcessor class that I don't want to make value-bound. Protocol-oriented programming is not only useful to create new taxonomies. Swift 3 extended this feature to protocols, which worked only for enumerations, structures, and classes in previous versions of the language. I have two protocols that define the basic structure of the interesting part of my project (the example code is nonsense but describes the problem): 1) A delegation protocol that makes accessible some information, similar to UITableViewController's dataSource protocol: 2) An interface protocol of the entity that does something with the information from above (here's where the idea of a "Protocol-First" approach comes into play): Regarding the actual implementation of the data processor, I can now choose between enums, structs, and classes. This would not be possible with a class hierarchy. That would mean a lengthy conditional statement, violating the Open-closed principle yet another advantage of protocol-oriented programming. With protocol extensions, we can attach method implementations to abstract protocols. We have characters, but we dont have a game yet. It looks like this. I, too, think that a "possibly weak" modifier would be a great addition to the Swift language as it would allow for less and cleaner code in such situations. Again, my objective is to show you protocol-oriented programming in practice. Protocol-oriented programming is not just a paradigm that works well only for game development.

You can make it a usual private method if you prefer.). The damage depends on the, Witches can also cast spells both warriors and witches. There are several different abstraction levels of how I want to process the information, therefore classes appear to fit best (however I don't want to make this an ultimate decision, as it might change in future use cases). Click again to start watching. Each language solves it in different ways. Notice that Fighter does not descend from Character anymore. But you often work on big projects with other developers. In OOP, you have to keep tracking of the instances so that they dont affect each other. Another of the advantages of protocols and protocol extensions is that any hierarchy can be extended modularly, without altering the existing types. We also have total freedom in declaring the other properties. Moreover, it works great with Swifts value types, i.e., structures and enumerations. First, we define a protocol that requires a conforming type to return an array of actions. Add another class which has a clear reference cycle, and run the following code as a CommandLine app: The code above generates the following output: Is your provider property a strong reference or a weak reference? The first type of character you find Dungeons-&-Dragons-style games is the warrior. Thats something we can do again with a protocol. You can send a feature request using Apple Bug Reporter, you can find Report Bugs link at the bottom of evrery developer page. Another great use of protocol-oriented programming is the ability to implement standard generic algorithms that are completely decoupled from concrete data structures and implementations. It seems using weak var & autoreleasepool in the Playground is not a good tool to detect reference cycle. Its declarative syntax composed of structures is wholly based on protocol-oriented programming. Notice that now our structures belong to a much broader inheritance hierarchy. With deeper hierarchies, this becomes more and more likely. Still, in this section, we will start with protocols. This is not a surprise. The pseudocode for the minimax algorithm above is missing an important detail. This is not dissimilar from inheritance in object-oriented programming. Instead, the compiler only forces us to put some useless code into the Character class. My understanding of clean protocol-oriented programming is that in the given case the protocol should really only define that there is a get-accessible ValueProvider, which is neither optional nor implicitly unwrapped everything else is to be handled by the actual implementation (please correct me if I'm wrong!). But, the deeper the hierarchy, the easier it is to break superclass invariants, to call methods of the superclass in the wrong place, or to forget it altogether. Now though, the maxHealth property is a variable. That works, but it would be a bit redundant since the minimax algorithm already contains a loop that does precisely that. If you want these to be able to attack characters, without behaving like them, you can make them conform to the Fighter protocol, avoiding the requirements of Character (the protocol might need to be renamed). If you are interested in seeing the code, you can find it in the full Xcode project on GitHub. In this article, I try to summarize the concepts from the video of WWDC.