In this article, I try to summarize the concepts from the video of WWDC. The protocol can then be adopted by a class, structure, or enumeration to provide an actual implementation of those requirements. I continued experimenting and ended up with this: Which compiles and at first glance appears to do what I want. You can make it a usual private method if you prefer.). And finally, implementing the minimax algorithm is just a matter of translating the above pseudocode into Swift code. Wizards are bad at fighting, but they can cast powerful spells. But a trained eye can already spot a few problems.

For instance, symmetric operations such as comparison. Do they also know that they should not do that? Wow, that's interesting. Exponential-time algorithms are expensive and practical only on small sets of data. The body of the method in the superclass has been removed. A cleric can fight like a warrior, so it has a weapon, an armor, and needs the same attack(_:) method of the Warrior class. Object-oriented programming is the most common paradigm in modern software development. Still, in this section, we will start with protocols. We can use Character as a generic type for this property since thats the only requirement we have for team members. While some solutions exist, they are less than ideal. Damage is based on attack, defense, power and magicResistance values, but they are not in the heuristic implementation. We can make any already-defined type conform to a protocol, without altering its declaration. Conceptually, minimax is not hard to understand. Many types in the Swift standard library already conform to it, including Int, String, and Date. Protocol-Oriented Programming comes in handy in a situation like this. 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. 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.

By the way, do you know how to propose this to Apple? Because of this code, types which conform to Collection must conform to Equatable too. And again, if later we add another class that descends from Spellcaster, we need to remember all that. Only the destination of an attack needs to be a character. After the introduction of protocol extensions in Swift, Apple started pushing protocol-oriented programming. Protocol-oriented programming is not just a paradigm that works well only for game development. At first sight, the code above looks fine. 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? 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. 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. There are few differences compared with the typical properties.

This makes it harder to break invariants because a protocol defines the appropriate access for each property. For example, in the Warrior and Cleric types, the defense property is computed and depends on the armor, while in the Witch struct its a constant stored property. It seems pretty nice, doesnt it? We have characters, but we dont have a game yet. This keeps their code simpler to read and more reusable across code bases. That's also reassuring because I wouldn't know where I introduced the cycle.

We know that a Character needs to have specific properties, so we express them as requirements in our protocol. 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. Another of the advantages of protocols and protocol extensions is that any hierarchy can be extended modularly, without altering the existing types. Lets now introduce a new character type in our game, the cleric. We can do that because in Swift functions are a first-class citizen, which means we can treat them like any other type. The game is played in alternating turns, in which each team can make a single move. Here we can leverage the fact that our character structures conform to the Actionable protocol to write a generic method. Right below the extension. Instead, they are requirements that any conforming type will have to meet, declaring its own properties. The solution of Swift and many other languages is to forbid multiple inheritance for classes. For games where players have many possible moves, getting to an end state is impossible even on the fastest computer. The characters in a team are chosen randomly, but there will be at least one character per type in each team. Otherwise, I always start with structures. Protocol-oriented programming is a highly flexible paradigm with many benefits. The typical game AI algorithm is minimax, which is used in all sorts of adversarial games, e.g., chess. We can store them in variables and pass them as parameters to other functions. 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. Learn on the go with our new app. In this guide I'll show you how to properly structure SwiftUI apps. The more you get defensive, the more the object loses its flexibility. We can now finally implement our concrete Warrior, Witch and Cleric types. Shall we start from the structures or the protocols? This is not a surprise. That made sense. To then be able to implement the state(performing:) method, we would have to write code to perform a deep copy of a Game instance. I will only focus on what is relevant to understand protocol-oriented programming or this article would turn into a book. Swift allows a class to descend from only one other class. UIViewController exists only to be subclassed. 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. Each character gets a single action each round. That already solves one of the problems of object-oriented programming. 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). The, Protocol requirements do not create interface pollution. The Game structure is where we will implement our game rules. This makes code more readable, and the next time you create a game, you can reuse the algorithm directly. The most evident benefit here is that we are now able to use multiple inheritance. A big part of the iOS SDK is object-oriented, including UIKit and Foundation, the most used frameworks in iOS development. That increases composability. Click again to start watching. If Swift had `possibly weak` modifier (weak for reference types, ignored for value types), we could have solved this issue in a cleaner manner. So, in this case, composition is better than inheritance. We still have no idea how we will implement these requirements for our Game type, but that does not matter. (Generally, pure Swift classes do not generate autoreleasing code.). Since we start having common characteristics, we need to create a Character superclass. This is how you can implement default values. Of course, in any strategic game, no move is good in isolation. But protocols alone are not enough for protocol-oriented programming. In more general programming terms, protocol extensions are mixins, which are available in other languages as well. To put it simply, the code above is trying to compare two double numbers using inheritance.

In fact, even Apple changed its mind in its Modern Swift API Design session at WWDC 2019. We can explicitly specify which types conform to our protocol, enabling the compiler to make stricter checks.

We could use these types in all sorts of games with different rules. We now need to extract the available actions from each character. You can find the complete Xcode project on GitHub. With deeper hierarchies, this becomes more and more likely. So, the algorithm evaluates moves recursively. Any type conforming to. 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). BaseDataProcessor has the valueProvider property which needs to be set when the class is initialized, whereas SpecificDataProcessor should never accept an external valueProvider during initialization. If you want to declare properties inside of a protocol, you need to stick with its special form of declaration. While protocol-oriented programming is a term that mostly refers to Swift, the concept is not new. reasoning iboutlet local why The more the object loses its flexibility, the more complicated your code gets. Notice the code where Element: Equatable right after extension Collection at the top. The problem though is that each line explicitly uses a character type. This is not a perfect metric, but it works since the algorithm will try to maximize the damage it makes to the opponent. 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. For that, we need to create some rules. Nevertheless, protocol-oriented programming can also be used with classes. When the depth reaches 0, the algorithm stops and returns the heuristic value of the current state. Adding more classes to our hierarchy adds new requirements to initializers. Lastly, there is one more feature regarding protocol extensions that I would like to introduce, the constraints. There are always parts in an apps architecture that need to be shared and globally accessible. Classes dont fit for the situations where type relationships matter. This is not evident in our game, because after all, all fighters are also characters. There is a simple Person class which conforms to Equatable be implementing func ==(lhsPerson:, rhsPerson:) method of Equatable . But later, you might want to add new types to the game, things like monsters, artifacts, and other creatures. Our only defense is using assertions. You probably think that you would never create such an instance in the first place. If you forget one, the compiler will stop you. That would mean a lengthy conditional statement, violating the Open-closed principle yet another advantage of protocol-oriented programming. 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). All the types that conform to that protocol will then inherit those methods. All it does is try all possible moves for a player and pick the best one. Most programming languages, including Swift, are object-oriented so this is the paradigm you pick first when you learn to program. Again, my objective is to show you protocol-oriented programming in practice. But how do we proceed? This hierarchy is flatter and more flexible than an object-oriented one. Its not just limited to value types like structures.

To expose them, we will start modelling the characters for our game using classes. The damage depends on the, Witches can also cast spells both warriors and witches. This would not be possible with a class hierarchy. 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.

I'm not ready to decide which is better, but hope your addressing this issue would help Swift team improve the language. Other than that, my code matches the pseudocode one-to-one. This is a pretty uninteresting function, except for one thing. Swifts value types, i.e., structures and enumerations, dont have an inheritance mechanism like classes. The compiler does not prevent that. The attacker only needs a weapon. And that gets worse when you dont own the code of superclasses, and you cannot read their implementation. Making EvaluatedPly conform to Comparable will allow us to use the min(_:_:) and max(_:_:) functions, as well any other function that works with comparable types. Since we are all pumped-up with protocol-oriented programming, the temptation might be to create a new protocol with these requirements. 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.

And, transitively, the Witch class will get these as well. What I will be showing is not necessarily the best approach to make a game. But thanks to the nature of protocols, we can get rid of many of the problems object-oriented programming has. When we deal with generic algorithms like minimax, it is useful to keep code generic and free from implementation details. When we pass values around, they are copied. Unfortunately, I dont have a wizard icon. Thats something we can do again with a protocol. To abstract this code, we need a way to use a type as a parameter. Here is the definition of the constraints from the Swift language website. If you havent watched the presentation, I strongly recommend that you watch the video at least once. Protocol-oriented programming solves many of the problems of object-oriented programming. While I will show it all below, I will gloss over its implementation details. Now one last question. You may use let or static to make properties or methods. 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. 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). We need to abstract it to make it reusable. At some points, you may want to have a default value for the properties or the methods inside of a protocol. Implementing our game will need a substantial amount of code. A WWDC 2015 session video describes the idea of Protocol-Oriented Programming, and I want to adopt this technique in my future apps. If you are interested in balancing and evaluating game rules, check this website. This is another advantage of protocol-oriented programming. First of all, Collection is a protocol which defines behaviours of sequences such as Array, Dictionary, etc. 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. The next type of character is the wizard. These properties allow us to define the attack(_:) method of Warrior and the castSpell(on:) method of Witch class. The, We dont need to alter the declaration of our types. You can send a feature request using Apple Bug Reporter, you can find Report Bugs link at the bottom of evrery developer page. First, we define a protocol that requires a conforming type to return an array of actions. This completes the implementation of our game logic. Lets see the example in action. The Character class encapsulates the common properties, which the Warrior and Witch class initialize independently.

But you often work on big projects with other developers. This enables the Warrior and Witch subclasses to implement the methods for attacks and spells, respectively. That also becomes a protocol in our new approach. With protocol extensions, we can attach method implementations to abstract protocols. It seems using weak var & autoreleasepool in the Playground is not a good tool to detect reference cycle. Protocol-oriented programming solves many of these problems, shifting the burden from the developer to the compiler. We have seen the problems object-oriented programming brings along. I am not going to pretend that this will be the best game in the App Store. Any type conforming to Character will get this computed property.

In our game, characters die when their health goes below 0. It looks like this. Windows Insider Build 20161 Brings Redesigned Start Menu & More! We can always try to work around these problems using a combination of computed properties, property observers, and assertions. The first type of character you find Dungeons-&-Dragons-style games is the warrior. You can use protocol-oriented programming at any level of the MVC pattern. This is a functional programming concept, so its outside of the scope of this article. Now OOPer says that I have no actual proof of a reference cycle, and I'll investigate this further. I wont go over the UI implementation for the game since there is nothing exciting in it related to protocol-oriented programming. A second feature is necessary: protocol extensions. 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. Thanks a lot for your efforts! Thats where the name of the algorithm comes from. 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? We will turn our classes into structures. However, in reality the specific data processors are tightly bound to the values that are processed (as opposed to the base processor, for which this is not true), such that I want to integrate the ValueProvider directly into the subclass (for comparison: often, UITableViewControllers are their own dataSource and delegate). We created the latter only when we needed to share code. Delegates and datasources are almost always weak references. Notice that Fighter does not descend from Character anymore. One of my favorite applications is to create well-structured network requests. I agree with you that in most cases, using a weak reference to the delegate object is the correct way. Then, we can make our types conform to that protocol through extensions.

They mostly rely on the programmer instead of using the compiler to check for the correctness of our code. Here we can see another couple of problems of inheritance. So, the algorithm cannot always go all the way down to a victory position. For inherited properties, the only solution we have is to make them optional. This site contains user submitted content, comments and opinions and is for informational purposes only. A game state is terminal when either team has no alive members left. This is not dissimilar from inheritance in object-oriented programming. So, we can declare our actions to store a generic function in a stored property. Views, view controllers, user defaults, URL sessions, and many other types in Apples frameworks are classes. The pseudocode for the minimax algorithm above is missing an important detail. To evaluate how good a move is, minimax uses a heuristic function to know how good the game state after such move.

This means we can move only part of the hierarchy to other projects without bringing every protocol along. If you are interested in seeing the code, you can find it in the full Xcode project on GitHub. Each language solves it in different ways. 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. Hoping to win because your opponent makes a stupid move is a bad strategy. We can do the same for the Spellcaster protocol. Of course, the algorithm assumes that each player will always pick the best move available. But despite their different signature, each method is a function from a character to another. I talk about recursion in-depth in my article on functional programming. I came up with a somewhat hacky solution and wonder if there is a cleaner way to achieve this: As bob133 suggested and you have already commented, making provider property a weak reference seems to be a natural solution.

If you go to check the link(the Swift language website), there is an example using Collection type. We want to know which move is best. In fact, its beneficial for common iOS development. We must initialize all stored properties with meaningless values, or our code wont compile. That means that we can change its value at any time in a subclass, even though that is conceptually wrong. This is another instance of protocol-oriented programming. 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. Another thing that is implicit in the code above is that the Warrior and Witch classes must provide values for maxHealth, health, defense and magicResistance. All you have left is guessing, hoping to trigger some assertion, or relying on documentation, which is often poor or non-existent. You can find the complete Xcode project on GitHub, you can find it in the full Xcode project on GitHub,, 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. To be able to implement the minimax algorithm, we need to: Again, we express all these requirements in a protocol. So, thanks to protocol extensions, they can still inherit method implementations. But I often recommend the opposite approach and start from concrete types, creating protocols only when needed. Each character can perform different actions, expressed by various methods. Lets take a look at the example from WWDC. But that only adds extra complexity without providing any compile-time check. I did not use any specific type coming from our Game structure. The code below is the Protocol-Oriented version of the previous code. All we would get runtime crashes, which we might not catch in our testing. Moreover, there is no risk of forgetting to implement any of the protocol requirements like it happened with classes. 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. The isHealer property will be useful later when we implement the game engine. It may be good to have some default announcement style through events. Again, these problems might seem trivial in our example, because the initializers are still manageable, and the attack(_:) methods implementation is small. Its easy to make an app by throwing some code together. There are several merits in adopting Protocol-Oriented approach in this case. 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. Thanks to the heuristic, the algorithm does not need to know about all the rules. Each character class has its own, predefined value that never changes. But again, the compiler does not enforce it. The minimax algorithm uses the min(_:_:) and max(_:_:) functions, which in Swift only work on types that conform to Comparable. 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. 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! When you create instances of a class, instances have the reference to exactly the same object. Youve stopped watching this thread and will no longer receive emails when theres activity. But without best practices and robust architecture, you soon end up with unmanageable spaghetti code. And finally, we can only create values from these three types. Languages like Java use abstract classes to avoid this problem, but Swift does not have a similar construct. The minimax(atDepth:maximizingPlayer:) method is a recursive method. While it might be apparent it in this simple example, thats less obvious with more complex superclasses. Instead, the compiler only forces us to put some useless code into the Character class. While clerics can fight, they have restrictions on their gear. But when playing a game, we dont care about that value alone. The rules of the game, instead, do not belong to characters. As an example for this article, we will create a small, turn-based fantasy game. I considered this, but found that it is easier to implement a "computed" self-reference which I expected not to generate reference cycles by design: I was surprised to see that my Playground/autoreleasepool experiments indeed indicated a reference cycle. Its declarative syntax composed of structures is wholly based on protocol-oriented programming. This problem is known as interface pollution. My codes structure is slightly different because the two branches of the if-else statement looked redundant, and I merged them into one. So I prefer to adapt the algorithm to return not only the value of a move but also the move. So the algorithm takes an extra depth parameter, which it decreases at each step. So we can create a new Spellcaster class with the repeated code. In Swift, protocols define the desired interface a type must implement to suit a particular task or piece of functionality. But if you know iOS development, you also know that it would be pointless. The problem of inheritance is that subclasses dont know anything about the invariants of a superclass. I'm a Software Engineer based in Vancouver. The last requirement of Minimaxable is the possiblePlies() method. No matter which one you pick to be at the top, the other will have to inherit methods it does not need. Any type that satisfies the requirements of a protocol is said to conform to that protocol. I will explain three major problems of OOP. The isDead property is the first example of a protocol extension. Swift 3 extended this feature to protocols, which worked only for enumerations, structures, and classes in previous versions of the language. To fully appreciate the versatility of protocol-oriented programming, you first need to understand the problems object-oriented programming presents. apply each ply to a game state, getting a new, resulting state. But witches cannot fight, so we dont want this functionality to be available at the Witch level. These empty instances can then creep into other parts of your code and create problems. So you will still have to use classes in your projects. Object-oriented programming is a fundamental component of software development. However, I respectfully disagree with your suggestion to make the ValueProvider a "possibly weak" property of the DataProcessor protocol, as this is more of an implementation detail that the protocol shouldn't be aware of. I hope you will feel the same way. This method compares given Person s name. I believe I understand what and why you disagree.