The Error-box™

Allows to declare a type that handles json deserialization errors gracefully

Kotlin adaptation of a swift implementation from MP0w

What does it do

Given the following data classes

    data class Person(val name: String, val city: String)
    data class Team(val persons: List<ErrorBox<Person>>)

And a potentially broken json

{
  "persons": [
    {"name":  "Nicolas", "city":  "Barcelona"},
    {"name":  "Alex"}
  ]
}

You would normally get a deserialization error, but with error box you get a list of error boxes that either contain the value or the error message.

val team: Team = objectMapper.readValue(teamJson)
println(team.persons)

💫 ✨

[Right(b=Person(name=Nicolas, city=Barcelona)), Left(a=com.fasterxml.jackson.module.kotlin.MissingKotlinParameterException: Instantiation of [simple type, class com.nicolattu.ErrorBoxTest$Person]...)]

How to extract the values

val team: Team = objectMapper.readValue(teamJson)
println(team.persons)
val validPersons = team.persons.mapNotNull { errorBox ->
    errorBox.getOrHandle { error ->
        // Log error or report metric here log.error(error.message)
        null
    }
}
validPersons shouldHaveSize 1

For more examples check ErrorBoxTest

Note that the ErrorBox is a type alias from https://arrow-kt.io Either<Exception, T>, and therefore has all the super powers of it see the doc