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Jamie Taylor
05/28/2020, 3:10 PMWhat's the general consensus on the best way to have a function that can fail in multiple different ways in Kotlin? I always thought we should use Result for that but just found out that it can't be the return type of a function. Should we just keep on throwing exceptions?
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Chantry Cargill
05/28/2020, 3:10 PMsealed classes are the way to go.
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Stefan Beyer
05/28/2020, 3:11 PMwhy cant it be in the return type?
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Chantry Cargill
05/28/2020, 3:11 PMIt’s experimental ^
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Jamie Taylor
05/28/2020, 3:12 PMso do people normally make a sealed class for generic result types for each project they do, or make a separate sealed result type for each different type of result or what?
it seems like having a standard one that provides functions like map and flatmap would be useful
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Sam Garfinkel
05/28/2020, 3:13 PM Copy code
sealed class Result
data class Result1(): Result
data class Result2(): Resultc
Chantry Cargill
05/28/2020, 3:14 PMThat’s a matter of style. You can easily create a general Result type, but it’s also a fair pattern to have multiple types under a sealed class specific to your use case.
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Sam Garfinkel
05/28/2020, 3:14 PMMonads are a good solution here
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Stefan Beyer
05/28/2020, 3:14 PMWhen I just need this in very few places in a project, I usually use own sealed classes. But if it is a common theme, using libraries like Arrow would make sense 🙂
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Sam Garfinkel
05/28/2020, 3:15 PMWith the sealed classes you can define two results, one that returns Exceptionally (fails) and one that Succeeds with a
val value: Any Copy code
sealed class Result
data class ExceptionalResult(val exception: Throwable): Result
data class Success(val result: Any?): Resultc
Chantry Cargill
05/28/2020, 3:19 PMIf you do go down the Arrow route, https://arrow-kt.io/docs/0.10/apidocs/arrow-core-data/arrow.core/-either/.
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Jamie Taylor
05/28/2020, 3:20 PMLots of sensible options, thanks
If you were starting a new project and needed a result type, is there any particular one you'd be more likely to go for?
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Chantry Cargill
05/28/2020, 3:22 PMI personally write my own, but as I say, it’s a matter of style.
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Stefan Beyer
05/28/2020, 3:22 PMand if you are writing a general solution yourself, dont use
Any Copy code
sealed class Result<T> {
data class Success<T>(val value: T) : Result<T>()
class ExpectedError<T>(val somethingThatHelpsToRecover: SomeType) : Result<T>()
class UnexpectedError<T>(val errorMessage: String) : Result<T>()
// ...
}☝️ 1
If you were starting a new project and needed a result type, is there any particular one you'd be more likely to go for?my personal opinion is: • try to avoid writing generalized (generic) result types. (because they get ugly really quickly) • if you are not comfortable writing a sealed class for every case, then use a library like arrow. (10 sealed classes may be ok, 1000 is just ridiculous)
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