Programming in Kotlin - Part 36: Mutable vs | Ray Wenderlich Videos

Learn the difference between the two types of collections.

This is a companion discussion topic for the original entry at

I don’t know why, but IntelliJ is giving me an unresolved reference error when I try to declare an ArrayList as you did in the tutorial. I’ve tried using Alt+Enter to import it properly, but it didn’t make any difference.

Have you tried to manually type the import? For example:
import kotlin.collections.ArrayList