Argonaut-在自定义解码器中返回错误

Question

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.

Answer 1

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)
}