CODEWITHSUNDEEP
scalaparametersconstraints
user1826663
user1826663

Reputation: 377

constraints on constructor parameters

Excuse me, but I'm new to Scala. I have a abstract class and a concrete class that inherits from the abstract class and implements its fields.

abstract class Element {
  var name: String
  var description: String
}

class ConcreteElement (var name: String, var description: String)extends Element

Is this right? Yes? I have many classes that inherit from abstract class Element. Now I want to put a check on the variable name, that I want to instantiate name only in accordance with certain constraints. Where do I put this control? Obviously in abstract class Element.

In Scala A variable declaration var x: T is equivalent to declarations of a getter function x and a setter function x_=, defined as follows:

def x: T
def x_= (y: T): Unit

So I decided to declare the variables in this way and posizionere my constraints in the getter method name.

abstract class Element {    
def name: String
def name_= (y: String): Unit = {CONSTRAINT}

var description: String
}

class ConcreteElement (var name: String, var description: String)extends Element

This reasoning is correct? ConcreteElement actually implements the fields of Element?

Upvotes: 1

Views: 436

Answers (1)

Yang Bo
Yang Bo

Reputation: 3728

Your def name_= works only if it has not been overriden by the sub-class. So I guess you need final to prevent it being overriden.

abstract class Element {
  protected var _name: String
  final def name: String = _name
  final def name_= (value: String) {
    if (isBadValue(value)) throw new IllegalArgumentException
    _name = value
  }
  var description: String
}
class ConcreteElement (protected var _name: String, var description: String) extends Element

Upvotes: 1

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