swift overloading return type

Rust has return type polymorphism rather than return type "overloading", but the difference only manifests for library authors; for API consumers the interface is the same either way. for foo(x: T) T must be a supertype of typeof(a)). [1]. This follows the precedent of throws.. I always thought unidirectional type inference (i.e. This post explores one way that the REPL bends normal coding rules to give you new powers when developing. Note 2: The parameter configuration is different between the two functions, not the parameter values like in the previous case. width + rhs. The only caveat, is that you need to specify the destination entity type (no implicit type). so the only way to tell them apart is the return value but with discardableResult you say it can be ignored. Different ways to overload the method. (The rust language ergonomics can be a good guide: try to balance "applicability", "power", and "context dependence". It would be enough to get an interview for me. to_string_t as shown is bait for undefined behavior, when combined with auto: It could be made safe by making to_string_t a template and forwarding from_string's argument into its storage, if things are not complicated enough already :). Yes. Again, when we code it like this, we don’t yet know the concrete type, but at compile time, Swift knows. When overloaded literals like maps can themselves contain literals, there are actually quite a few possible overloadings to choose from. Where is the energy coming from to light my Christmas tree lights? We would also need a way to determine which return type to choose: it can be a function parameter, or a value stored elsewhere, etc. How can I show that a character does something without thinking? :-). There are two other overloadable types of operators known as prefix and postfix, like the old ++i and i++ operators of yore. How to define optional methods in Swift protocol? It's just not going to be maintainable. That's probably what code reviews are for. The limits idea at the end seems fine, for example. This can often help us create neat APIs. height) } } The following calls work but are not very nice imho. For your own types, you can have the compiler translate. People don’t really call it overloading, but it has many similarities. This method overloading functionality benefits in code readability and reusability of the program. This is not a great example because a string conversion by nature requires error-checking and should. :P. Ha! Hopefully, your function does some other things (side effects) than provide a return value: in that case, there may be little use in discarding the result of a function that does nothing but provide that result, and one may probably be better off not calling it in the first place. I would say that, especially by C++ standards, this is surprisingly simple, easy to understand, and fully featured - even the extensible template-based version. I agree. Is there any text to speech program that will run on an 8- or 16-bit CPU? We can put people on the moon, but we can't write a safe constructor in c++. There are two ways to overload the method in java. See Line no. * Subtyping. The code shows some creativity and shows you know how to work with templates. Open Xcode and create a new playground by going to File ▶ New ▶ Playground. It also has parametric polymorphism. Swift brings together three features that can be hard on type inference: * Overloaded literals. Now if the side effects (i.e. Derivation of curl of magnetic field in Griffiths. The most well known example is the `.collect()` method, which can collect an iterator into many different types of collections. Table with two different variables starting at the same time. Changing the parameters is also possible but it would be pretty silly in this already-silly example: Note: I'd obviously only do this if the additional parameters actually make sense. Let's see what happens if we stop insisting on any one of the three conditions. and (String)->JSON? Is there a difference between Cmaj♭7 and Cdominant7 chords? In the previous article, we saw how Swift allows overloading by just the return type. Why is my half-wave rectifier output in mV when the input is AC 10Hz 100V? The art of programming is knowing when to break the rules, similar to most artistic pursuits. Why do you say "air conditioned" and not "conditioned air"? And then you would need more advanced algorithms to find a path through the type maze efficiently. Thanks for contributing an answer to Stack Overflow! ... You could create a subtype of type Enum called Genre. The CustomStringConvertible protocol and the description computed property let you print a friendly String representation of the Vector. … With these kind of overloads, explicitly stating the type tells Swift which function you want to call: With these kind of overloads, explicitly stating the type tells Swift which function you want to call: Here is the gist of it. rev 2020.12.8.38142, Stack Overflow works best with JavaScript enabled, Where developers & technologists share private knowledge with coworkers, Programming & related technical career opportunities, Recruit tech talent & build your employer brand, Reach developers & technologists worldwide, You have two functions with the same name and different signatures (String) ->[String: Any]? width, y: lhs. 49, d3 = d1 + d2; here, d1 calls the operator function of its class object and takes d2 as a parameter, by which operator function return object and the result will reflect in the d3 object. Hmm, this looks like the Scala implicit conversion trick. In the case of limits it is not very powerful, it's just a little syntax sugar. Method overloading increases the readability of the program. Pick the Blank template and name your playground CustomOperators. At compile time, Swift figures out that the concrete return type of makeShape() must be Square. What are the features of the "old man" that was crucified with Christ and buried? A quick google doesn't bring anything obvious here. Should the method just not be overloaded and have a different name instead? I know we have Codable and stuff but lets assume that I want to support SwiftyJSON optionally by creating an extension that only compiles when SwiftyJSON can be imported. Also consider the alternative (eg in this case you can just write class functions on your type or use existing libraries). Swift: How to deal with method overloads where only the return type differs and the result is discardable? This piece shows that the author seems to be resourceful, creative and has a reasonably good understanding of C++. This is explicitly supported in Rust (with generics). Asking for help, clarification, or responding to other answers. This is our interface: I would now like to support other Libraries optionally. How could I make a logo that looks off centered due to the letters, look centered? All the above syntax are valid to create a function that takes no parameters and doesn't return value. It feels like most C++ devs don't know SFINAE - I'd rather find someone who knows deeper bits of the language and encourage them to use their talents appropriately. Great article, but don't try this at home (or work). The above syntax func funcname() -> () is also equivalent to func funcname() -> Void because Void is just a typealias of (). What is the best way to deal with this problem? Would a change like this land in production? Apparently Haskell supports overloading on return type: https://stackoverflow.com/a/442291/. This is the reason that alternative general purpose languages are popular - just because you can write it in C++ doesn't mean you should :). ), but it's just unnecessary complication at this point. An operator is a special symbol or phrase that you use to check, change, or combine values. What is an escrow and how does it work? your coworkers to find and share information. He also advices against going over the top on it, though, so he agrees with “you can doesn’t imply you should”. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. As many on the /r/cpp thread for this said, the ultimate result: The return-type overloading helps if you want to use non-static member initialization: Yeah, this is something that might have made sense before auto, and in fact IIRC there were some Boost libraries that used this trick (Boost.Assign? Instead this author was a bit too clever by half; a shorter article more focused on practical limitations might have been much more helpful to coders. Good for at least three PhD theses. I don't think this is even significantly more code than a Haskell version would be, and the error messages and limitations are not significantly worse either. This is possible: Here we cannot (easily) extend the functionality via extensions; rather, we'd need to touch the enum and function code with all the possible options every time we want to add a new return type. Well, let's do just that! Was Stan Lee in the second diner scene in the movie Superman 2? - [Instructor] Swift will let us have multiple functions … with the same name, … as long as their function type or signature is different. One of the nice things about Swift, is that we can do this. Well, I just realized I messed up left and right in my post so... we all do it. Yeah, agreed, there's a time and a place for this stuff. The return-type overloading helps if you want to use non-static member initialization: struct Foo { int x = init("x"); double y = init("y"); string z = init("z"); }; for not very good reasons you can't use auto there and having to specify the type twice is ugly. BUT: Since we have a discardableResult calls like. Overload resolution basically enumerates all functions with the name foo that are accessible in the current scope and removes those that cannot be called with a (i.e. https://littlegreenviper.com/miscellany/swiftwater/swift_fun... A string can contain anything and certainly not conform to its expected type. All we lose is the shared name. https://docs.microsoft.com/en-us/cpp/cpp/auto-cpp?view=vs-20... https://play.rust-lang.org/?version=stable&mode=debug&editio... https://medium.com/@jreem/advanced-rust-using-traits-for-arg... https://learn.adacore.com/courses/Ada_For_The_CPP_Java_Devel... https://blog.rust-lang.org/2017/03/02/lang-ergonomics.html. First, you define a variable named simpleSum and set its value with the assignment operator (=). } func output(text:String) { print(text) } func output(text:String, num:Int) { print("\(text)\(num)!") By using our site, you acknowledge that you have read and understand our Cookie Policy, Privacy Policy, and our Terms of Service. Operator Overloading. To learn more, see our tips on writing great answers. As functions do practically the same thing, it makes sense to use function overloading. Practical example. Why does US Code not allow a 15A single receptacle on a 20A circuit? Overload with different return type in Java? Redefining Everything with the Swift REPL Our first entry on the REPL covered just the basics, showing how to use the REPL to experiment with Swift as you learn the language. To be able to do that, we could start by overloading the + operator to accept two CGSize instances as input, and output a CGPoint value: extension CGSize { static func +(lhs: CGSize, rhs: CGSize) -> CGPoint { return CGPoint ( x: lhs. You are going to use the string concatenation operator under the hood, since you can imagine the whole thing like this: Before diving into coding, think how you would solve the problem and break it into steps. The type of newValue is the same as the return value of the subscript. > Thus, auto i = to_string_t{"7"}; does not work as intended. Operators are those little symbols like +, *, and /, and Swift uses them in a variety of ways depending on context – a string plus another string equals a combined string, for example, whereas an integer plus another integer equals a summed integer. But I've seen it used in end seemed like sensible places in a production codebase and wouldn't say "never do this." Easy JSON formatting October 10, 2015; I am a bit confused here, are you talking about something that would require templates in C++? Derived class’s display() function has return type ——- String. In general, I don't like to try risky new things in prod right away. How to find where a method is defined at runtime? Stack Overflow for Teams is a private, secure spot for you and There is at least one alternative, however. Someone will have to maintain that code. String is a sub-type of Object. Seems ok. Can you compare nullptr to other pointers for order? Do you have any references about "omnidirectional type inference" in rust? As for the template error messages, since this is just one layer of templates, I suspect that they will be quite decent - especially considering that even one std::string-related error message is easily a few lines of almost completely irrelevant gibberish (does anyone actually use non-default char_traits???). We could put people on the moon. It'd help with the edge case I showed... "safe" is a strong word though, doesn't handle this one: I meant to write "safer" but the "r" fell through :). If it's an improvement, I'll leave it in, and as I figure out how to write clean code or fix the bugs with it, I'll start considering it in prod. height + rhs. This is best illustrated by an example. But it also doesn’t mean you should not. Swift Function Overloading By Return Type October 11, 2015; As Objective-C developers, we often forget that we can overload functions by return type. I always had a beef with "turbo smart C++ tricks" like overloading ! 26, Distance operator+(Distance &d2), here return type of function is distance and it uses call by references to pass an argument. Is it illegal to market a product as if it would protect against something, while never making explicit claims? Add the following code to your playground: Here you define a new Vector type with three properties conforming to two protocols. Hence we can use it as return type in overridden display() function instead of type Object as in Base class. Depends, sort of. For example, the function `Default::default()`, where Default is a trait that you can easily implement for your own types, too. Why is the word order in this sentence other than expected? Operator overloading Question 1/12: This code is valid Swift – true or false? I really do not wanna do that since that would lead to a lot of calls that look like this: The more I think about the problem it occurs to me that there might just not be a good solution for this.. Actually, removing @discardableResult wouldn't work, and _ = Foo().perform(query: "") wouldn't compile, it would still have the same ambiguity: it's not that the compiler is being nitpicky, but it has literally no way of knowing which of your two functions to call! Some people describe this split as "type deduction" vs "type inference," that is, C++ has deduction, Rust has inference. Yes. let aObject2_Subscript = aObject2[0] let aObject2_Poem = aObject2_Subscript.poem // Next, test the accessor methods. The issue below isn't actually overloading; it is template argument deduction. Sure, it's 2020, but I'm pretty sure there's quite a lot of people who have used C++ but cannot come up with the code you see in the final version. Now I may be dead wrong, and there may be something better out there… We'll find out soon enough. Let's eliminate the first condition, and try using a single return type. Thirdly – last but definitely not least – opaque types are … … Defining multiple functions with the same name … is called function overloading … and it's very useful in cases … where you need constant functionality … with dependent or computed results. It can be used to return some value for function/method , and property without revealing the concrete type … It's my opinion that AAA is an unwise goal; uninformed use of 'auto' can lead to unintended copies. Jan 23, 2015. Don't go there. This may be a high cost for simply maintaining "result discardability," but then it may also allow us to abstract away some details, only unwrapping the "payload" when needed, which can have its own benefits. Not a big deal. You don’t need both. Which shouldn't be a problem I guess, but only as long as you're just an API consumer and don't have to produce one. This ad keeps all of Swift by Sundell free for everyone. Is it always smaller? I can only imagine 2050, There are probably more moving parts in a C++ compiler than the whole lunar landing program. If you had general overload on return type, you could write big nested expressions and force the compiler to examine all the overload possibilities. Java provides the facility to overload methods. Basic Operators¶. let bObject1: A = mainObject.returnIndexedElement(1) let bObject2: … :) They would have to tell me when they felt it was appropriate and inappropriate to use such a trick to get a hire. How can I add a few specific mesh (altitude-like level) curves to a plot? site design / logo © 2020 Stack Exchange Inc; user contributions licensed under cc by-sa. It was a pleasant surprise, when I found it out. the call to output(x: "Swift") triggers the statement inside the function func output(x:String). If you can, please check this sponsor out, as that directly helps support this site: Architecting SwiftUI apps with MVC and MVVM: Although you can create an app simply by throwing some code together, without best practices and a robust architecture, you’ll soon end up with unmanageable spaghetti code. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. As Objective-C developers, we often forget that we can overload functions by return type. By changing number of arguments; By changing the data type; In Java, Method Overloading is not possible by changing the return type of the method only. This would have been a good launching-off point to talk about the linker, or language design, which we did a bit of towards the end but in the wrong context, in my opinion. type casting type alias protocol anonymous class method method overloaded override ref parameter parameter array return closures static func overloading override inout, & params return C# lambdas method ref, & parameter array Swift protocol C# interface enumerations functions Swift enum static func C# enum (no equivalent) attribute (no equivalent) memory management automatic reference Just like every other class in Java, String class extends the Object class i.e. Use an else clause. Well, this is what I've been able to gather on this interesting problem. How to understand John 4 in light of Exodus 17 and Numbers 20? Inferring types in C++ (and languages with type deduction) basically looks like this: In Rust (and languages with type inference), inferring types can look like that: To see how this plays out in your parent's comment, I adapted the code from: https://docs.microsoft.com/en-us/cpp/cpp/auto-cpp?view=vs-20... [1]: https://medium.com/@jreem/advanced-rust-using-traits-for-arg... Found a good source eventually: https://learn.adacore.com/courses/Ada_For_The_CPP_Java_Devel... Overloading in C++ needs to be done sparingly so the compiler doesn't run into multiple possible conversions, which result in complex and confusing error messages. We infer not types but type bounds (ranges). Rationale: The async follows the parameter list because it is part of the function's type as well as its declaration. Swift Function Overloading . With enough effort, you could write optimizers for functional programming that way, ones that figured out when you can create a pipeline and avoid storing an intermediate result. Opaque return types is a new language feature that is introduced in Swift 5.1 by Apple. But that can be handled as well. Maybe I'll write some throwaway code or a test that uses the new thing. Your point about long/int/short is more about the complexities of subtyping and/or implicit conversions than about return type overloading. For me it looks like the easiest solution is to remove discardableResult. This is our interface: class Foo { @ Swift does guarantee that such functions will in fact return to their actor to finish executing. What fun! Hint: Swift is a type-safe language, so it won't let you mix types by accident. It might be interesting to think about what behavior you'd expect from this line, and why. Following is the example of using equivalence operators to check for equivalence of our own custom type in a swift … in adverts? We can also use this in an extension. This is quite interesting. function int generateNumber ( int MaxValue) { return rand * MaxValue } function int generateNumber ( int MinValue, int MaxValue) { return MinValue + rand * (MaxValue - MinValue) } This is known as the overloading of the operator. 1) Method Overloading: changing no. Lets assume I've written a Framework in Swift that does stuff purely with native Swift Types. And it is obvious that return-type overloading is not usable in situations where the desired return type is not known, as in the auto example. The type of a reference to a function or initializer declared async is an async function type. * Overloading. An additional short-and-sweet example, using HashMap: Er, you haven't heard about Rust's new feature where it treats all common metasyntactic variable names as interchangeable? this is my first question and I hope you guys can help me out. Is it possible to have different return types for a overloaded method? How to hide keyboard in swift on pressing return key? As you can see from the top, this is just a function in Swift, but instead of a text name, we have a symbol as the name. The method overloading is a single class can have multiple methods with the same name but they should differ in signature or number of parameters and return type of the method. Both will ultimately fail to compile, so it will be up to the user of the API to avoid doing either. If the side effects are identical between the two overloaded functions, you can factor them out into a single function: Note that this can also be done via extensions as long as they re-use existing functions and only overload them with different signatures and/or return types. output(text1: "Good N", num: 8) In some circumstances you can use templates to approximate this with less surprising edge cases in exchange for not being as transparent in the common case. As with computed properties, you can choose not to specify the setter’s (newValue) parameter. I would say the from_string code has a few more footguns), [1] https://blog.rust-lang.org/2017/03/02/lang-ergonomics.html. (Of course advanced APIs can also be created that help third parties easily write extensions… If it's worth the effort.). But, as with overloading, you can't do it on return type. I doubt we are able to do it now in a 10 year time frame. I was going to include Ada in my comment, I was sure I'd read that it supports overloading on return type, but I couldn't find a supporting source with a quick google. Create the result variable and assign its initial value … The Bitwise AND operator will return the result as 1 only when both input bits are equals to 1 otherwise it will return 0. Here in the above program, See Line no. I thought the essay might be useful or informative, but about a third of the way through I realized that this was one of these "look how clever I am" essays. 2. Need of Function Overloading. These type of functions do not take any input and return value. edit: this is pretty much the only case I have used this trick. Rust also supports it, and it's actually very commonly used. A comment suggested to remove discardableResult. But rust doesn't even has function overloading. Lets assume I've written a Framework in Swift that does stuff purely with native Swift Types. Once an operator is declared, it can be associated with a type method or top-level function. C++ 'auto') was good enough but I have been surprised to find omnidirectional type inference very useful in Rust... for example, constructing an empty collection to pass as the parameter to a function. // let failObject = mainObject[0] // However, this will work, because the class has only one subscript method defined. Delete all the default code so you can start with a blank slate. If you get reasonable push back, don't use it. Sure, there are places where it's needed, an helps, but 'almost always'... not in my code base. As Objective-C developers, we often forget that we can overload functions by return type. This can often help us create neat APIs. In Swift, Ternary Precedence is defined lower than Default Precedence and higher than Assignment Precedence. Operator overloading is the practice of adding new operators and modifying existing ones to do different things. Here is some code i'd like to write: template class engine1 {}; template class engine2 {}; template