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. That would mean a lengthy conditional statement, violating the Open-closed principle yet another advantage of protocol-oriented programming. But when playing a game, we dont care about that value alone. A cleric can fight like a warrior, so it has a weapon, an armor, and needs the same attack(_:) method of the Warrior class. Now though, the maxHealth property is a variable. If the Game type were a class instead, any move would change the state of the actual game. So you will still have to use classes in your projects. Swifts extension can make it possible. Love podcasts or audiobooks? Here are some examples: Before we proceed, a little disclaimer. It is then possible to use these algorithm implementations on any type, by conforming to such provisions. If you are interested in balancing and evaluating game rules, check this website. And that's true we sometimes don't want to tell if the delegate is of value type or reference type . I'm not ready to decide which is better, but hope your addressing this issue would help Swift team improve the language. This completes the implementation of our game logic. Apple disclaims any and all liability for the acts, omissions and conduct of any third parties in connection with or related to your use of the site. Its not possible to create values with type Character, Fighter or Spellcaster, which would not make sense. Notice that, again, this solves some of the problems of object-oriented programming. We need to abstract it to make it reusable. Moreover, there is no risk of forgetting to implement any of the protocol requirements like it happened with classes. All the types that conform to that protocol will then inherit those methods. To put it simply, the code above is trying to compare two double numbers using inheritance. After making a move, it considers all the possible replies, then all the possible responses to those replies, and so on, until it finds a winning position. A second feature is necessary: protocol extensions. Click again to start watching. So, we can declare our actions to store a generic function in a stored property. Instead, they are requirements that any conforming type will have to meet, declaring its own properties. Wizards are bad at fighting, but they can cast powerful spells. This is a functional programming concept, so its outside of the scope of this article. If we follow that blueprint, we would then have to generate all the possible plies for the first step, call the algorithm on each one, and then pick the one with the highest value. Protocol-oriented programming is not just a paradigm that works well only for game development. Its easy to make an app by throwing some code together. I've been playing around with Swift 2.0 for the last couple of days in order to understand this new approach, and am stuck at trying to make it work with the Delegate Pattern. We can use Character as a generic type for this property since thats the only requirement we have for team members. But these are not great solutions. I did not use any specific type coming from our Game structure. The body of the method in the superclass has been removed. We also have total freedom in declaring the other properties. The Initializable protocol requires conforming types to have an initializer without parameters. As the name implies, protocol-oriented programming is founded on protocols. I wont go over the UI implementation for the game since there is nothing exciting in it related to protocol-oriented programming. The minimax algorithm uses the min(_:_:) and max(_:_:) functions, which in Swift only work on types that conform to Comparable. This problem is known as interface pollution. The function allEqual() compares each element in the given collection and returns true if all elements are equal. For more about generic where clauses, see Generic Where Clauses. Notice also that maxHealth is back to being a static property. 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. However, subclasses that inherit from BaseDataProcessor and adopt ValueProvider seem to override that implementation internally, so this is not an option. We still have no idea how we will implement these requirements for our Game type, but that does not matter. I hope you will feel the same way. If you are interested in creating compelling games, check this website on game design. That works, but it would be a bit redundant since the minimax algorithm already contains a loop that does precisely that. That means you can create instances of it, even if it does not make any sense in our game. The more the object loses its flexibility, the more complicated your code gets. However, this is not a solution as it produces a reference cycle, which can be seen in a Swift playground: Another option might be to add class constraints to the protocol definitions. First, we define a protocol that requires a conforming type to return an array of actions. I continued experimenting and ended up with this: Which compiles and at first glance appears to do what I want. I talk about recursion in-depth in my article on functional programming. apply each ply to a game state, getting a new, resulting state. So, thanks to protocol extensions, they can still inherit method implementations. Since our Game structure is a value type, we can quickly create copies in the state(performing:) method and then apply a move to it. This is another instance of protocol-oriented programming. Protocol-oriented programming solves many of the problems of object-oriented programming. You are right, when run as a command line app, there's indeed no reference cycle. In that way, the. Each character can perform different actions, expressed by various methods. But thats only because we already did the abstraction work in the previous section. The characters in a team are chosen randomly, but there will be at least one character per type in each team. Even worse, this would impose implementation restrictions on entities that adopt this protocol. 
One of my favorite applications is to create well-structured network requests. These are not stored properties like they were in our classes. Shall we start from the structures or the protocols? Protocol-oriented programming solves many of these problems, shifting the burden from the developer to the compiler. If you are interested in seeing the code, you can find it in the full Xcode project on GitHub. In Swift, protocols define the desired interface a type must implement to suit a particular task or piece of functionality. But that only adds extra complexity without providing any compile-time check. 
Swift allows a class to descend from only one other class. Adding more classes to our hierarchy adds new requirements to initializers. Object-oriented programming is a fundamental component of software development. If you havent watched the presentation, I strongly recommend that you watch the video at least once. That means that we can change its value at any time in a subclass, even though that is conceptually wrong. When the depth reaches 0, the algorithm stops and returns the heuristic value of the current state. So we can create a new Spellcaster class with the repeated code. My proposal may be a short-cut workaround until Swift protocols can become what we expect and need. This means we can move only part of the hierarchy to other projects without bringing every protocol along. That already solves one of the problems of object-oriented programming. But protocols alone are not enough for protocol-oriented programming. All postings and use of the content on this site are subject to the, Additional information about Search by keywords or tags, Apple Developer Forums Participation Agreement. Our only defense is using assertions. Swift 3 extended this feature to protocols, which worked only for enumerations, structures, and classes in previous versions of the language. These can only be implemented with reference types. Otherwise, I always start with structures. These are usually healing spells. While I will show it all below, I will gloss over its implementation details. You can find the complete Xcode project on GitHub, you can find it in the full Xcode project on GitHub, https://matteomanferdini.com/wp-content/uploads/2019/08/gameplay.mp4, Model-View-Controller in iOS: A Blueprint for Better Apps, Become an iOS Developer in 2020: The Ultimate Guide, Passing Data Between View Controllers in iOS: the Definitive Guide, Network Requests and REST APIs in iOS with Swift (Protocol-Oriented Approach), JSON Decoding in Swift with Codable: A Practical Guide, Protocol-oriented programming is also beneficial at the, Warriors can attack both warriors and witches. Warriors are strong fighters that can use a vast array of weapons and armors. The Team and TeamMember types are namespaced, to make it clear that they belong to the Game implementation. 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. The, Protocol requirements do not create interface pollution. Notice the code where Element: Equatable right after extension Collection at the top. Here we can leverage the fact that our character structures conform to the Actionable protocol to write a generic method. Do they also know that they should not do that? For instance, symmetric operations such as comparison. Click again to stop watching or visit your profile/homepage to manage your watched threads. Proceeding down the class hierarchy of the previous example, we find the Fighter class. Any type conforming to. Swifts value types, i.e., structures and enumerations, dont have an inheritance mechanism like classes. Each structure conforms to more than one protocol, inheriting all the properties and methods in their extensions. Other than that, my code matches the pseudocode one-to-one. Imagine you are imitating competitions in code. How To Develop An On-Demand Grocery Delivery App Like Tesco? When you create instances of a class, instances have the reference to exactly the same object. Thats because multiple inheritance creates ambiguity in case of common ancestors and overrides. I am using this example to fit the didactical purpose of this article, not to teach you how to make games. That increases composability. So I prefer to adapt the algorithm to return not only the value of a move but also the move. Thats everything for this article! Since clerics can also cast spells, we also want to share code between the Cleric and Witch classes. I believe I understand what and why you disagree. So, in this case, composition is better than inheritance. The isHealer property will be useful later when we implement the game engine. SwiftUI slightly improves the situation. Right below the extension. Implementing our game will need a substantial amount of code. We can store them in variables and pass them as parameters to other functions. Again, these problems might seem trivial in our example, because the initializers are still manageable, and the attack(_:) methods implementation is small. While some solutions exist, they are less than ideal. In this guide I'll show you how to properly structure SwiftUI apps. And, transitively, the Witch class will get these as well. If you ever played chess, you know that there is no point in capturing the opponents queen if he is going to checkmate you on his next move. reasoning iboutlet local why Protocol-Oriented Programming(POP) is a new approach to programming which addresses the problems related to Object-Oriented Programming. We can explicitly specify which types conform to our protocol, enabling the compiler to make stricter checks. The typical game AI algorithm is minimax, which is used in all sorts of adversarial games, e.g., chess. To abstract this code, we need a way to use a type as a parameter. So, despite all my advice above, this is a case where its better to start with a protocol (in software development, no rule is absolute). This hierarchy is flatter and more flexible than an object-oriented one. Now OOPer says that I have no actual proof of a reference cycle, and I'll investigate this further. When we pass values around, they are copied. While it might be apparent it in this simple example, thats less obvious with more complex superclasses. But witches cannot fight, so we dont want this functionality to be available at the Witch level. Another thing to pay attention to is that before introducing the Character class, the maxHealth property was conveniently implemented as a static constant. 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? Using extensions, we then make each of our character types conform to Initializable. The, We dont need to alter the declaration of our types. Tips & Tricks While using Swift with Obj-C, Every iOS developer should know these Xcode tricks, class Label: Ordered { var text: String = "" }, let codingEvent = CodingChallenge(prize: "A trip to San Fransisco"), // Will print "Kenta gets Trip to San Fransisco! The inheritance structure itself is not so flexible because of the following reasons. which basically seems surprise operation anything turn into As the saying goes, when all you have is a hammer, everything looks like a nail.. Any type that satisfies the requirements of a protocol is said to conform to that protocol. At first sight, the code above looks fine. This means that, at each step, the algorithm tries to maximize the heuristic value for one player and to minimize it for the other one. With deeper hierarchies, this becomes more and more likely. That's also reassuring because I wouldn't know where I introduced the cycle. 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. Learn on the go with our new app. The next type of character is the wizard. In our game, characters die when their health goes below 0. This method compares given Person s name. The last requirement of Minimaxable is the possiblePlies() method. By the way, do you know how to propose this to Apple? So, even if you have to use classes for some tasks, you can still alleviate some of the problems of object-oriented programming using protocols and extensions before you reach for class inheritance. This makes it harder to break invariants because a protocol defines the appropriate access for each property. You can find the complete Xcode project on GitHub. It seems pretty nice, doesnt it? With protocol extensions, we can attach method implementations to abstract protocols. Even if it was a new paradigm, it quickly got widespread adoption in Swift programming and iOS development. Classes dont fit for the situations where type relationships matter. It seems using weak var & autoreleasepool in the Playground is not a good tool to detect reference cycle. This enables the Warrior and Witch subclasses to implement the methods for attacks and spells, respectively. With objects, instead, we pass around references to a shared instance. The rules of the game, instead, do not belong to characters. Many types in the Swift standard library already conform to it, including Int, String, and Date. At WWDC in 2015, the powerful concept called Protocol-Oriented Programming(POP) was introduced. This is a pretty uninteresting function, except for one thing. That made sense. And thats where we get into yet another problem of object-oriented programming. The attacker only needs a weapon. A protocol defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality. After the introduction of protocol extensions in Swift, Apple started pushing protocol-oriented programming. Protocol-oriented programming is not only useful to create new taxonomies. (Generally, pure Swift classes do not generate autoreleasing code.). Object-oriented programming is the most common paradigm in modern software development. The Game structure is where we will implement our game rules. Trying all the moves and checking the results accounts for those game rules already. Superclass must have something inside of the method body. Thats called the diamond problem. We will turn our classes into structures. Admittedly, this is not the most exciting iOS game youll ever play, but considering how little code we wrote, its already impressive that it is playable at all. So, even if paradigms like protocol-oriented programming and functional programming can be useful, object-oriented programming is not going away. The Character type is a full-fledged class. Since Competition has a default implementation of the method, you dont even need to write the method in the conforming type (in this case CodingChallenge struct). Of course, in any strategic game, no move is good in isolation. If Swift had `possibly weak` modifier (weak for reference types, ignored for value types), we could have solved this issue in a cleaner manner. The algorithm can be summarized in a few lines of pseudocode, which I took from its Wikipedia page: Minimax has exponential time complexity. Now with the protocols mentioned in my first post, I can't (and don't want to) tell if the delegate is of value type or reference type, and you cannot have weak or unowned references to value types. If you go to check the link(the Swift language website), there is an example using Collection type. But again, the compiler does not enforce it. This is another advantage of protocol-oriented programming. We need a way to identify each team member individually since there can be more than one character of each type on each team. Lets start defining a protocol for our characters. This allows us to keep our hierarchy flat, removing the initialization burden from your types. Congrats! This is how you can implement default values. For our game, we can sum the health of all characters in a team and subtract the health of the characters in the other. We now need to extract the available actions from each character. For that, we need to create some rules. All you have left is guessing, hoping to trigger some assertion, or relying on documentation, which is often poor or non-existent. The first type of character you find Dungeons-&-Dragons-style games is the warrior. OOP is far from perfect though, and sports several problems a skilled developer needs to consider. Still there is a place where the "possibly weak" approach would make sense: But even then, I'm not sure if a weak reference is the better solution per se. We have seen the problems object-oriented programming brings along. Conceptually, minimax is not hard to understand. They cannot wear armor, because it prevents them from making the movements necessary to cast spells. To evaluate how good a move is, minimax uses a heuristic function to know how good the game state after such move. Thanks to it, we can then create the makeCharacters(from:upTo:) generic function, using a CSwift generic with an Initializable type constraint. This keeps their code simpler to read and more reusable across code bases. Still, in this section, we will start with protocols. We can make any already-defined type conform to a protocol, without altering its declaration. You probably think that you would never create such an instance in the first place. What I will be showing is not necessarily the best approach to make a game. You may use let or static to make properties or methods. I understand that this way I probably wouldn't need a computed property at all (and that might be reason enough), but is there any actual downside of "var provider: ValueProvider { return self }" that I'm not aware of? For that, we will use protocol-oriented programming again. Languages like Java use abstract classes to avoid this problem, but Swift does not have a similar construct. The more you get defensive, the more the object loses its flexibility. Nevertheless, protocol-oriented programming can also be used with classes. For example, if we make Spellcaster descend from Fighter, it will inherit the weapon and armor properties, and the attack(_:) method. Classes, structs, or enums conforming to a protocol will have the same kind of functionality. In that form, all it does is return the heuristic value for a game state. I'll mark your answer as correct, thanks! Its kind of a troublesome task to implement the announcePrize(to person:) every time you make some types which are conforming to Competition . But without best practices and robust architecture, you soon end up with unmanageable spaghetti code. Without Actionable, we would have to downcast each character to its concrete type and then call the appropriate method. One of the great features of protocols is that any Swift type can conform to them. This site contains user submitted content, comments and opinions and is for informational purposes only. The game is played in alternating turns, in which each team can make a single move. The damage depends on the. For that, we need a function that randomizes the members in each team, making sure that each side gets at least one character per type. A big part of the iOS SDK is object-oriented, including UIKit and Foundation, the most used frameworks in iOS development. The TeamMember has a character property for composition. Notice that Fighter does not descend from Character anymore. Here we can see another couple of problems of inheritance. 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. Each level adds more initialization burden for subclasses. Damage is based on attack, defense, power and magicResistance values, but they are not in the heuristic implementation. 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. Clerics are holy fighters which can also cast spells they receive from their god. From the rules above, it looks like the members of each team need some new properties. Here is the definition of the constraints from the Swift language website. A round ends when all the characters have moved. The code below is the Protocol-Oriented version of the previous code. There are several merits in adopting Protocol-Oriented approach in this case. The Problems of Object-Oriented Programming, Modeling the Business Domain with Protocol-Oriented Programming, Extending Existing Types and Hierarchies Without Altering Them. Of course, the algorithm assumes that each player will always pick the best move available. We must initialize all stored properties with meaningless values, or our code wont compile. In this article, I try to summarize the concepts from the video of WWDC. I can define a base processor class, on top of which I can build several case-specific processors (not possible with structs and enums): Up to here everything works like a charm. And again, if later we add another class that descends from Spellcaster, we need to remember all that.
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