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jsonscalaerror-handlingargonaut

Argonaut - Returning an error in a custom decoder

I'm trying to implement an Argonaut JSON decoder instance that converts JSON strings to instances of my enum QuestionType. The problem is that if the string isn't a valid, the returned DecodeResult should be an error, and I'm not sure how to do that.

My code currently looks like this:

implicit def QuestionTypeDecodeJson: DecodeJson[QuestionType] = {
    DecodeJson(c => for {
      typeName <- c.as[String]
      questionType = QuestionType.fromString(typeName).get
    } yield questionType)
  }

QuestionType.fromString(typeName) returns an Option. Ideally, instead of using get, I would like to convert the Option to a DecodeResult, with either the contents of the Option, or an error state if it's None.

I could use the constructor of DecodeResult, but to be honest the signature of that is quite confusing to me (I'm new to scala). It seems that it requires a CursorHistory object, and I'm not sure what I'm supposed to pass in there.

Solution

  • DecodeResult object has an 'ok' and a 'fail' method.

    implicit def QuestionTypeDecodeJson: DecodeJson[QuestionType] = {
    DecodeJson(c => for {
      typeName <- c.as[String]
      questionType = DecodeResult.ok(QuestionType.fromString(typeName))
    } yield questionType)
}