Modeling with Scala case class

Question

I'm attempting to model responses from REST APIs as case classes which I can use pattern matching on. I thought it would be a good fit assuming inheritance, but I see that this is deprecated. I know there are already questions related to case classes and inheritance, but my question is more about how you would model the following the "right way" here without inheritance. I started with the following two case classes, which work fine: ``` case class Body(contentType: String, content: String) case class Response(statusCode: Int, body: Body) ``` i.e. a REST call would return with something like: ``` Response(200, Body("application/json", """{ "foo": "bar" }""")) ``` which I could pattern match like: ``` response match { case Response(200, Body("application/json", json)) => println(json) case Response(200, Body("text/xml", xml)) => println(xml) case Response(_,_) => println("Something unexpected") } ``` etc. which works fine. Where I ran into trouble is: I'd like helper extensions for the…

Accepted Answer

There are several reasons why case classes shouldn't be subclassed. In your case, the problem becomes that `OK` is another type than (a subtype of) `Response`, therefore the match fails (even if the arguments match, the type doesn't match).

You will want custom extractors, instead. For example:

```
case class Response(code: Int, body: String)
object OK {
  def apply(body: String) = Response(200, body)
  def unapply(m: Response): Option[String] = m match {
    case Response(200, body) => Some(body)
    case _                   => None
  }
}

def test(m: Response): String = m match {
   case OK(_) => ":-)"
   case _     => ":-("
}

test(Response(300, "Hallo"))  // :-(
test(Response(200, "Welt"))   // :-)
test(OK("Welt"))              // :-)
```

There are few more examples of custom extractors in this thread.

Modeling with Scala case class

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