CODEWITHSUNDEEP
scalapattern-matching
Shivam Sahil
Shivam Sahil

Reputation: 4921

Scala 2.13: avoid repeated case class conversion?

I have a pattern matching for sealed trait which expects two of one case classes as shown below:

 expressions.head match {
      case SingleValueExpression(value,_operator,_ignoreCase) => filter ++ FromScala(
        SingleValueExpression(value,_operator,_ignoreCase)
      ).transform(ToJson.string)
      case MultipleValueExpression(value,_operator,_apply,_instances) => filter ++ FromScala(
        MultipleValueExpression(value,_operator,_apply,_instances)
      ).transform(ToJson.string)
    }

You can see that even after decoding the case classes, I am recreating the case class in the next step:

case MultipleValueExpression(value,_operator,_apply,_instances) => MultipleValueExpression(value,_operator,_apply,_instances)

Is there a way to match the pattern such that I could check if the instance is of that case class and then use the value as it is instead of destructuring it and recreating the same case class?

Upvotes: 0

Views: 62

Answers (1)

Levi Ramsey
Levi Ramsey

Reputation: 20541

To just check the type in a pattern match, use :, like so:

expressions.head match {
  case sve: SingleValueExpression => filter ++ FromScala(sve).transform(ToJson.string)
  case mve: MultipleValueExpression => filter ++ FromScala(mve).transform(ToJson.string)
}

You could even have something like

val fromScala =
  expressions.head match {
    case sve: SingleValueExpression => FromScala(sve)
    case mve: MultipleValueExpression => FromScala(mve)
  }

filters ++ fromScala.transform(ToJson.string)

You can alternatively use @ to do extraction and binding in one case (e.g. you want to match based on a component of a case class but save the overall match):

case sve @ SingleValueExpression(value, _, _) if somePredicate(value) =>
  // sve is the overall SingleValueExpression, and value is also available in this branch

Upvotes: 3

Related Questions