Programming in Scala Forum - Understanding 'var' and 'val'

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Understanding 'var' and 'val'

2 replies on 1 page. Most recent reply: Mar 15, 2018 11:32 PM by jinf Fei

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akash dhasade

Posts: 1
Nickname: akash58
Registered: Jun, 2017

Understanding 'var' and 'val'

Posted: Jun 28, 2017 4:11 AM

var defines a mutable object and val defines an immutable object. So as suggested in the book if I define ->
import scala.collection.mutable.Set
val set = Set(1,2,3)
set += 4

It works. Since I have imported a mutable set.

Similarly if I would do as follows:
import scala.collection.immutable.Set
var set = Set(1,2,3)
set += 4

It should give me an error because my set is immutable but it doesn't!

Why??

Guke Huang

Posts: 1
Nickname: guke
Registered: Dec, 2017

Re: Understanding 'var' and 'val'

Posted: Dec 19, 2017 7:31 PM

You misunderstand the immutable object that val refers to. The keyword val defines a object that can not be reassigned, but it's just a refrence. That means val can not refer to others.

jinf Fei

Posts: 3
Nickname: jm8371
Registered: Mar, 2018

Re: Understanding 'var' and 'val'

Posted: Mar 15, 2018 11:32 PM

Yes, you can think that val variable point a "box", you can put a apple into box or put a bannel into box. But you can not change the "box".

So you can change Set context but you can not change the Set object.

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