Hi I have a data class named `Error` that I want to use to r

Question

Hi I have a data class named `Error` that I want to use to represents errors occuring in my api not exceptions but state different than what the user expected when they made their request When I use it now Kotlin defaults to the java lang Error Can I change this default or should I pick a different name

Minsoo Cheong · Answer

``` SinceKotlin 1 1 public actual typealias Error = java lang Error``` this typealias exists in the kotlin stdlib TypeAliases kt file I think that picking a different name would be the easiest way if keeping your class name isn t that important

Eivind · Answer

Yeah I changed it to `ApiError` Not ideal but close enough until something better Thanks

Max Ferrier · Answer

If you have more results class like your Error one you can have a SealedClass Results with Error success etc

Eivind · Answer

Yup I did initially have `Success` and `Error` in a `sealed class Outcome` but I figured the <http vavr io|vavr io> library has better support for all the functions I d have to implement on my Outcome class anyway fold map mapleft flatmap etc so I just started using that instead

Ties · Answer

< Eivind> if you want to use FP in kotlin you might want to look at the Arrow library slightly smiling face it is vavr but for kotlin

Ties · Answer

It has an Either class for this exact purpose also shameless self promotion <https www youtube com watch v=Wojgv2MeMGU amp t=80s> if you want to learn more about how to use this it assumes no knowledge about eithers or that way of thinking

Eivind · Answer

Thanks that s neat slightly smiling face I ve always used vavr for FP in Kotlin and Java Would you say it s more idiomatic to Kotlin Would I be better off using Arrow Some of the code I work with is java and kotlin so it isn t always pure kotlin code does that matter

Ties · Answer

It works a bit different depending on what you are using In most ways Arrow is better than vavr because it integrates really well because of kotlin features like extension functions and coroutines in kotlin code Collection wise standard kotlin might be better to use than vavrs collections they are less optimal since vavr uses linked list tricks underneath but it gives the same convenience of having map flatmap etc without having to call stream And you don t need to use collections from vavr which have the same name as java util collections and will probally cause confusion at some point The thing that sold me on Arrow was the either comprehension like the for yield from scala which takes care of most flatMap magic when using eithers the video will also show that bit

Ties · Answer

Kotlin also has the Result type which is basically an Either but has a Throwable as a Left slightly smiling face

Ties · Answer

if this fits your use case you don t even need a framework

Eivind · Answer

I needed an either esque container where I could have my own error type as the left I fiddled with making one myself but the monad type being available in vavr meant I didn t have to reinvent the wheel as far as fold map etc goes if I just used vavr slightly smiling face Because it s hard to tell if a throwable reveals too much information or not so I d rather replace the throwable with something I know will be safe to let bubble all the way up But I ll check out arrow soon that sounds nice also never heard of the `Optics` data type what on earth nerd face

Ties · Answer

The video will also explain Optics slightly smiling face but thats a construction to make easy changes in deeply nested immutable data structures