Result is all I need

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• There's certainly situations where this pattern creates some tricky ambiguity, but more often than not Result is quite an ergonomic pattern to work with.

  In case it's useful for anyone, here is a simple plug-in-play TypeScript version:

  ```

  type Ok<T = void> = T extends undefined ? { ok: true; } : { ok: true; val: T; };

  type Err<E extends ResultError = ResultError> = { ok: false; err: E; };

  type Result<T = void, E = ResultError> = { ok: true; val: T; } | { ok: false; err: E | ResultError; };

  class ResultError extends Error { override name = "ResultError" as const; context?: unknown; constructor (message: string, context?: unknown) { super(message); this.context = context; } }

  const ok = <T = void>(val?: T): Ok<T> => ({ ok: true, val: val, } as Ok<T>);

  const err = (errType: string, context: unknown = {}): Err<ResultError> => ({ err: new ResultError(errType, context), ok: false, });

  ```

  ```

  const actionTaker = await op().then(ok).catch(err);

  if (result.ok) // handle error

  else // use result

  ```

  I will be forever grateful to the developer first introduced to this pattern!

  by DrakeDeaton
• I am not a fan of function chaining in the style advocated in the article. In my experience functional abstractions always add function call indirection (that may or may not be optimized by the compiler).

  You don't need a library implementation of fold (which can be used to implement map/flatmap/etc). Instead, it can be inlined as a tail recursive function (trf). This is better, in my opinion, because there is no function call indirection and the trf will have a name which is more clear than fold, reducing the need for inline comments or inference on the part of the programmer.

  I also am not a fan of a globally shared Result class. Ideally, a language has lightweight support for defining sum/union types and pattern matching on them. With Result, you are limited to one happy path and one error path. For many problems, there are multiple successful outputs or multiple failure modes and using Result forces unnecessary nesting which bloats both the code for unpacking and the runtime objects.

  by thefaux
• I've been toting around and refining a Result<> implementation from project to project from Java 8 onwards. Sealed classes in 17+ really make it shine.

  I wish Oracle et al. had the courage to foist this into the standard library, damn the consequences. Whatever unanticipated problems it would (inevitably) create are greatly outweighed by the benefits.

  I've written Pair<> about a dozen times as well.

  by topspin

•     } catch (exception: Exception) {
        // log exception
        throw exception
      }
  

  Probably the most harmful snippet ever written. Every blog post about errors has something similar written, regardless of the programming language. Please, don't write, suggest or even pretend that this should exist.
  by valcron1000
• Since this looks like Kotlin, worth pointing out that there is a kotlin class in the standard library called Result. I've been using that for a few things. One place that I'm on the fence about but that seems to work well for us is using this in API clients.

  We have a pretty standard Spring Boot server with the usual reactive kotlin suspend controllers. Our api client is different. We were early adopters of kotlin-js on our frontend. Not something I necessarily recommend but through circumstances it was the right choice for us and it has worked well for us in the last five years. But it was a rough ride especially the first three of those.

  As a consequence, our API client is multiplatform. For every API endpoint, there's a suspend function in the client library. And it returns a Result<T> where T is the deserialized object (via kotlinx serialization, which is multiplatform).

  On the client side, consuming a result object is similar to dealing with promises. It even has a fold function that takes a success and error block. Basically failures fall into three groups: 1) failures (any 4xx code) that probably indicate client side bugs related to validation or things that at least need to be handled (show a message to the user), 2) internal server errors (500) that need to be fixed on the server, and 3) intermittent failures (e.g. 502, 503) which usually means: wait, try again, and hope the problem goes away.

  What I like about Result is making the error handling explicit. But it feels a bit weird to client side construct an Exception only to stuff it into a Result.error(...) instead of actually throwing it. IMHO there's a bit of language friction there. I also haven't seen too many public APIs that use Result. But that being said, our multiplatform client works well for our use.

  But I can't expose it to Javascript in its current form; which is something I have been considering to do. This is possible with special annotations and would mean our multiplatform client would be usable in normal react/typescript projects and something I could push as an npm. But the fact my functions return a Result makes that a bit awkward. Which is why I'm on the fence about using it a lot.

  So, nice as a Kotlin API but good to be aware of portability limitations like that. You would have similar issues exposing Kotlin code like that to Java.

  by jillesvangurp

•     fun register(registrationRequest: UserRegistrationRequest): UserDTO {
          return success(registrationRequest)
              .flatMap { validRequest ->
                  throwIfExists(validRequest.email) { authService.userExists(validRequest.email) }
              }.flatMap {
                  runWithSafety { authService.register(registrationRequest.email, registrationRequest.password) }
              }.getOrThrow()
      }
  

  There appears to be some useless code there. Why is validRequest.email being passed to throwIfExists twice? Why is throwIfExists implemented to return the email if the following line (runWithSafety) just ignores that returned email and instead gets the email from registrationRequest.email?
  by Thorrez
• Not a fan. Code branches and this is Good Thing(TM). Result violates the single responsibility principle and tries to make what are distinct paths into a single thing. If your language has exceptions and returned values as distinct constructs then obfuscating them with Result means you end up fighting the language which becomes apparent fairly quickly. It's also a frustrating experience to want to interact with returned values directly and constantly have to deal with a polymorphic wrapper.
  by iandanforth
• I always think more languages should support Result… but only to handle expected error states. For example, you may expect that some functions may time out or that a user may attempt an action with an invalid configuration (e.g., malformed JSON).

  Exceptions should be reserved for developer errors like edge cases that haven’t been considered or invalid bounds which mistakenly went unchecked.

  by tyleo