If we copy down optional members and create optional or non-optional abstract members, then there's no way for your derived class to say "I don't want to implement that member". The desirability isn't the missing piece of this - it's clear that this would be nice - but rather that we lack a solution without negative side effects that outweigh what is ultimately a pure convenience thing. Ultimately, it's not clear which trade-off makes most sense here. One should be able to reason about it as copying the bare minimum required to actually satisfy the interface, and optional properties are not required (by definition) so they wouldn't be copied. This comment outlines the conceptual difficulty of what this actually should mean. Can anyone Identify the make, model and year of this car? Expected behavior: Apart from boilerplate and maintenance burden on abstract class, this behavior also causes unnecessary breaking changes to upstream libraries where only an abstract implementation of the contract exist; requiring them to do new releases whenever parent interface changes.

The desirability isn't the missing piece of this - it's clear that this would be nice - but rather that we lack a solution without negative side effects that outweigh what is ultimately a pure convenience thing. Have a question about this project? If foo is optional in FooFace, then does FooClass have an implicit abstract foo? TypeScript not enforcing the return type of optional methods defined in interfaces implemented by parents of classes, Use optional method syntax for enter/exit/visit.

not warrant it. // Class 'FooClass' incorrectly implements interface 'FooFace'. However I can illustrate how easily this could happen: All changes to IComponent#onRemoval (e.g. How does interfaces with construct signatures work? Sum of Convergent Series for Problem Like Schrdingers Cat. That's a breaking change, though. this seems like an obvious and basic feature for any object-oriented language: how come it hasn't been implemented ? Making that (presumably rare case) explicit with a "never" seems like the best approach. This code is currently legal and would become illegal: That's a good point. resharper typescript generation code javascript inset declarations commands pressing provides alt types member type // how it looks like, trying to call test.run with no correct properties will give you error. Ok came here to say wtf . How can this be missing ? Trending is based off of the highest score sort and falls back to it if no posts are trending. For what it's worth, I'm interested in this because Closure Compiler (very recently) allows abstract classes to not redeclare unimplemented interface methods, and I don't want to see code taking advantage of this feature be more problematic to migrate to TypeScript. I'm actually completely surprised that L['x'] and M['x'] are invalid rather than also number | undefined. Is it too confusing/surprising if only required properties are implicitly copied? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. I think the basis is sound, and this should be perfectly viable. Extract 2D quad mesh from 3D hexahedral mesh.

If I knew how to solve it, I'd have done so already . There actually is a way to copy optional members concretely and have a subclass declare that they don't want to implement it [playground]: Today's state is both error-prone and unergonomic, and the only sound thing to do if a class wants to declare it won't implement an optional property is to carry around the tombstone to guarantee nothing implements it in an incompatible way. If I knew how to solve it, I'd have done so already, I'll try to find a solution and ASAP I found it, I'll share it here. Did Sauron suspect that the Ring would be destroyed? If it were being invented today, I'd argue that implicit inheritance is safer and more ergonomic, but since the safety improvement is only partial and it's actually a breaking change, it's possible that the churn to roll it out ends up outweighing the benefit. Is "Occupation Japan" idiomatic? Already on GitHub? If we don't copy down optional members, then we've created a "hole" in your type that will allow a derived class to accidently overwrite them with a mismatched type: The last problem is of course present today, but doing some of the copying would seem to create the appearance that we were doing more than was actually happening. Connect and share knowledge within a single location that is structured and easy to search. How do you explicitly set a new property on `window` in TypeScript? properties with call signatures; would they be considered abstract? You need to re-write all of the members/methods in the interface and add the abstract keyword to them, so in your case: There was a suggestion for it: Missing property declaration in abstract class implementing interfaces but it was declined for this reason: Although, the convenience of not writing the declaration would be rev2022.7.21.42639. Please, would someone update on the state of this issue ? What's the difference between a magic wand and a spell. I was not following the discussion on optional properties but I was only referring one of the limitation of the existing behavior of the type system on abstract classes. @RyanCavanaugh what's the process to actually put together a proposal for this? typescript constructor Missing property declaration in abstract class implementing interfaces, Design patterns for asynchronous API communication. @gkdn Can you point to a concrete project where this occurred? @RyanCavanaugh Yes, definitely. Since I'm not actively developing in TS but only interoping with it, I cannot give you a concrete project where this occurred. Was there a Russian safe haven city for politicians and scientists? Any news about it? (); or not?

// Be aware that I have removed the inner class Job just for test purpose. abstract Class implements Interface should imply interface Class extends Interface. You can now choose to sort by Trending, which boosts votes that have happened recently, helping to surface more up-to-date answers.

There are outstanding issues with "just doing it" outlined above that haven't been addressed yet. How can I use parentheses when there are math parentheses inside? I'm not sure if it was mentioned before but; Can a human colony be self-sustaining without sunlight using mushrooms? Is there a political faction in Russia publicly advocating for an immediate ceasefire? Overall it seems like we'd be trading off understandability for convenience here. Defining series before enumitem list starts, Scientific writing: attributing actions to inanimate objects. > So, how can I help to solve this issue? FYI, just dropping "Ugh can't believe it's not fixed already" comments does not change our view of feature priorities. That said, it's only a minor safety improvement: you could still assign a string to m.opt and try to read a number out of s.opt, which is a result of the fact that writable properties are properly invariant rather than covariant, so that's a deeper problem that's not really feasible to ever fix. Same, most OO languages have the similar feature. nice, the possible confusion/complexity arising from this change would // error: Type '(x: I) => void' is not assignable to type 'undefined'. (instead of occupation of Japan, occupied Japan or Occupation-era Japan). I'd be interested in how much actually breaks in the real world, though, and whether any of the breakages actually point to design flaws in the underlying code. Are strongly-typed functions as parameters possible in TypeScript? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Sign in Making statements based on opinion; back them up with references or personal experience. Interfaces are used for defining a contract regarding the shape of an object. changing return type) or API additions to IComponent (e.g. Use constructor to pass in properties to the class. Sign up for a free GitHub account to open an issue and contact its maintainers and the community. I understand how it works now, but I wanted to know what holds @RyanCavanaugh from implementing. Expanding on your example. I have some interfaces that explain the behaviors, and when I implement them in the abstract class, I expect the abstract to inherit those behaviors. By clicking Sign up for GitHub, you agree to our terms of service and // error: Type 'string | undefined' is not assignable to type 'undefined'. members appear on the type, is it all properties, methods, or Why does abstract class have to implement all methods from interface? // Property 'foo' is missing in type 'FooClass'. How did this note help previous owner of this old film camera? If we copy down optional members and create optional concrete members, then we're going to copy down optional properties (I'm presupposing here that differentiating properties and methods is right out) and you won't have any way for you to say "I don't want to have that property". This is what I want to do: But run in Q has typings of (any, any), when I expect for it to have typings of (job: Agenda.Job, done: (err? @RyanCavanaugh Thank you for the thoughtful response, sorry for my delayed reply. Thank you for all those things that you do for this community, Abstract classes that implement interfaces shouldn't require method signatures. Same here, I cannot imagine that there's a problem to solve that, from my p.o.v. Find centralized, trusted content and collaborate around the technologies you use most. Asking for help, clarification, or responding to other answers. Announcing the Stacks Editor Beta release! But in typescript, I should implement the interface's methods in an abstract class that introduces redundant and unnecessary boilerplate codes. Why did the gate before Minas Tirith break so very easily? In TypeScript, compiler complaints that the class incorrectly implements the interface: Here Absis an abstract class and so why do we need to implement the interface over there? by examine the declaration, it is not clear which How do I cast a JSON Object to a TypeScript class? To learn more, see our tips on writing great answers. What are the purpose of the extra diodes in this peak detector circuit (LM1815)? Thanks for contributing an answer to Stack Overflow! // This declaration is necessary today to make the TS type-system happy. it's just a fix in the compiler and won't lead to any issue on runtime. You signed in with another tab or window. Please engage in meaningful discourse with the content of the thread so far instead of idly complaining. Why is it required for abstract classes to implement named interfaces completly? We'd need some suggestion for how to implement this in a way that isn't starkly surprising or bad in any of the outlined scenarios. If the assignment to m needs to be legit, then M should have been explicitly declared with opt? If a creature's best food source was 4,000 feet above it, and only rarely fell from that height, how would it evolve to eat that food? Adding properties to a class via decorators in TypeScript, Typescript declaration: Merge a class and an interface. What happens if I accidentally ground the output of an LDO regulator? I believe I addressed the concerns in that comment pretty thoroughly. Sorry, maybe I wasn't clear earlier. to your account, Search Terms: abstract class implements interface. : never, and then your example type checks. privacy statement. All choices seem bad. The answer is that it should copy all properties, and that if it's intended to not have the property, then the implementer should declare it as optional never, which is a win for consistency, understandability, correctness, and safety all at once. Can you provide some details about negative impact that you are worrying about? Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Enforcing the type of the indexed members of a Typescript object? If I knew how to solve it, I'd have done so already . Abstract classes that implement interfaces don't need to define abstract type definitions to satisfy interface. The text was updated successfully, but these errors were encountered: Apparently this can be worked-around with class and interface merging: That seems redundant, though, I still think this should be fixed. In my real-world use case (in which I'm currently using the interface/class merging workaround), my interface actually only has optional methods, I just thought I'd leave that out of this example for simplicity. I'm going to use the workaround but I'd really appreciate knowing more about a future proposal ! Unfortunately you're going to break code when you improve safety, by definition. optional? This is all intuitive enough for required members but we can't figure out what should happen to optional members. Another simple option, but it is still redundant is: I also encountered this issue.

I wonder if there's an incremental "half-way" sort of approach, where an initial version could support only non-optional properties in an intuitive way, and then a potential future update could later add support for the optional ones? : Error) => void). You can get what you want with a slight trick that defeats the compile-time errors: This trick takes advantage of Typescript's Declaration Merging, and was originally presented here and posted on a related SO question here. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Can a timeseries with a clear trend be considered stationary? Well occasionally send you account related emails. @shicks is exactly right: the way you say "I don't want to have that property" should be the same as the way you do so when extending the interface, with never: By contrast, you expect K['x'] to be number | undefined. However Library 2 wouldn't need an update and a re-release if the type system didn't require redeclaration of the abstract methods. I don't understand why this option seems bad?

add onFoo) are are source-incompatible changes in TS today and requires AbstractFancyComponent to be updated and new release for Library 2 to be pushed. // Would not be an error, but could break at runtime, // proposal: implicit if no 'x' is specified, // proposal: implicit if no 'm' is specified, // "I'm not going to implement this and nobody else better either".