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kotlinlang

```
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 `=`?

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

It does still use operator overloading of course :wink:

<@U5UU34LPK> you are referring to the `+` in immutable list example right?

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