are collections completely immutable by default if you use val?

# getting-started

[Bernhard]

are collections completely immutable by default if you use val?

[rocketraman]

No. val just means the variable reference cannot be reassigned. The referenced object itself can be mutated if the object supports mutation.

[Bernhard]

ok, weird. I have a data class which defines a set as val something and I can't do: data.something.remove(stuff)

[Bernhard]

or kotlin sets just different from java sets in terms of signatures?

[rocketraman]

Is it a Set or MutableSet?

[Bernhard]

Set

[Bernhard]

converting from java atm

[Bernhard]

I suppose I either need MutableSet then or copy

[rocketraman]

Kotlin has mutable and immutable collections. List, Set are immutable (really not immutable, but read-only, as the underlying collection is the same, just the interface is different).

[rocketraman]

Yup, on your last comment

[Bernhard]

thanks

[adam-mcneilly]

You don't always need copy -> you can do mySet.toMutableSet() and it's a little more readable. 🙂