Scala: Cannot change object attribute of var: Assignment to val

Question

I am confused as to what the issue is here. I have an function:

def myFunc(activity:Activity):updatedActivity = {
    //var updatedActivity:Activity = activity <- This doesnt work either
    var updatedActivity:Activity = activity.copy()

    val params =  Params (
      "Attribute"
    )

    updatedActivity.parameters = params
    updatedActivity
}

This will not work, because reassigning an attribute updatedActivity.parameters = params throws a reassignment of val error, even though updatedActivity is a var. How can I update the activity parameter I passed in and return it?

updatedActivity may be a var, but if it's a case class then the attribute parameters is definitely a val, this is why you are getting the error. — Tanjin
– Tanjin, Commented Oct 26, 2017 at 16:31

galbarm · Accepted Answer · 2017-10-26 16:37:29Z

4

updatedActivity may be a var but class Activity has a field called parameters which is a val. So it must be assigned during construction.

if its a case class, try this:

def myFunc(activity:Activity):updatedActivity = {   
    val params =  Params (
      "Attribute"
    )

    activity.copy(parameters = params)
}

If it is not a case class, it has to be passed as a regular parameter to the constructor, i.e.

new Activity(params)

edited Oct 26, 2017 at 16:37

answered Oct 26, 2017 at 16:32

galbarm

2,5633 gold badges34 silver badges54 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

adrice727 · Accepted Answer · 2017-10-26 16:31:58Z

1

I'm assuming that Activity is a case class. Even though updatedActivity is a var, the underlying value (case class) is immutable, meaning that you can reassign updatedActivity, but cannot change the current value in place. Instead, you can just return:

updatedActvity.copy(parameters = params)

answered Oct 26, 2017 at 16:31

adrice727

1,49212 silver badges17 bronze badges

Collectives™ on Stack Overflow

Scala: Cannot change object attribute of var: Assignment to val

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related