CODEWITHSUNDEEP
scaladefault-constructor
rupert160
rupert160

Reputation: 1531

Scala compile error: member of method parameter not visible to class method

I am getting a compile error of:

value txn is not a member of Charge
new Charge(this.txn + that.txn)
                           ^

with the following Scala class definition:

class Charge(txn: Double = 0){
  def combine(that:Charge): Charge = 
    new Charge(this.txn + that.txn)
}

Explicitly declaring txn as a val allows it to work:

class Charge(val txn: Double = 0){
  def combine(that:Charge): Charge = 
    new Charge(this.txn + that.txn)
}

I thought val was assumed? Can somebody explain this? Is it a problem with my understanding of the default constructor or the scope of the method?

Upvotes: 0

Views: 215

Answers (2)

Pritam Kadam
Pritam Kadam

Reputation: 2527

In scala, you can define classes in two forms, for ex.

  • class Charge(txn: Double) -> In this case scala compiler compiles it to java like below
public class Charge {
  ....
  public Charge combine(Charge);
  ....
  public Charge(double);
  ....
}

As you can notice in compiled java code, there is no public accessor for txn Let's look at another variation of Charge class, If you define like this class Charge(val txn: String), it gets compiled to below

public class Charge {

  ...
  public double txn();
  ...  
  public Charge combine(Charge);
  ...
  public Charge(double);
  ...
}

As you can see, in this case compiler generates public accessor for txn hence you are able to access that.txn when you mark it as val

  • case class Charge(txn: Double): This is data class for which scala generates getters, equals and toString for you. You can compile this class

  • scalac Charge.scala

  • javap -c Charge.class And then see what it generates

Upvotes: 3

Nebehr Gudahtt
Nebehr Gudahtt

Reputation: 189

What you pass to constructor is essentially constructor parameters whose scope is limited to the constructor. If you want to make them visible from the outside, you have to declare them as vals or reassign to some other vals in the constructor body.

Upvotes: 2

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