``` var immutableList = listOf(1, 2, 3) immutable...

# getting-started

[harry.singh]

var immutableList = listOf(1, 2, 3)

immutableList += 4

Since plusAssign operator is not defined on a Collection in Kotlin, what does immutableList += 4 really do. It can't add the element to the the List as it is immutable unlike ArrayList. So does it first create a new List from the plus operator and then assign it to the reference variable through =?

[Ruckus]

Yes, this one does not use operator overloading, so it is interpreted literally as

immutableList = immutableList + 4

Note that if this was a mutable list, you'd get an error from ambiguity.

[harry.singh]

yep because both mutableList = mutableList + 4 and mutableList.plusAssign(4) would be applicable in this case and hence compiler will generate an error for the ambiguity

[harry.singh]

right?

[Ruckus]

Exactly

[karelpeeters]

It does still use operator overloading of course 😉

[harry.singh]

@karelpeeters you are referring to the + in immutable list example right?

[karelpeeters]

Yes.

[harry.singh]

Also if there was no plus operator defined on List, we would never get compiler error in the case of mutable list for += right?

[karelpeeters]

Yep.

[Ruckus]

@karelpeeters Fair point 🙂