followup about scala constructor oveloading

Question

This is a followup question to Scala constructor overload? I'd like a case class constructor that operates on a restricted form of the input and so overrides, rather than overloads the constructor:

abstract class Expr

case class RegExpr(regex : Regex) extends Expr {
  override def this(regex : Regex) = {
    if (regex.toString contains "*") 
     throw new Exception("Restricted class of regular expressions: cannot contain Kleene star.")
    else if (regex.toString contains "|")
      throw new Exception("Restricted class of regular expressions: cannot contain disjunction.")
    else this(regex)
  }
}

This doesn't compile; I've tried a couple different iterations of this, but they all come back to the compiler telling me it expects 'this', but 'if' is found instead. How do I get the behavior I want?

score 5 · Accepted Answer · answered Dec 11 '12 at 08:23

5

There is no need for two constructors. Just add the check inside the class, they will be run at construction time.

case class RegExpr(regex: Regex) extends Expr {
   if (regex.toString contains "*") throw ...
   if (regex.toString contains "|") throw ...


}

answered Dec 11 '12 at 08:23

Didier Dupont

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3

`require(!regex.toString.contains("*"), "...")` is more idiomatic argument test. – senia Dec 11 '12 at 10:40
Also, the final else is unnecessary. – yakshaver Dec 11 '12 at 18:22

followup about scala constructor oveloading

1 Answers1