hey why can't I use "removeFirst" here? <https://leetcode.com/playground/EViekAXG>

# getting-started

[Varun]

hey why can't I use "removeFirst" here? https://leetcode.com/playground/EViekAXG

[Varun]

managed to get a deque implementation working, but for learning purposes want to understand why i can't use removeFirst

[jbnizet]

Probably because the version of Kotlin that leetcode uses predates version 1.4, and removeFirst has been added to the standard lib in version 1.4: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/remove-first.html