This trivial piece of code in a Playground sets the Running wheel spinning forever, and it never prints output. Other attempts to create a 2D array have led to an infinite Indexing loop in my real project. I can't go to Xcode 10 due to my hardware being too old. Has anyone got working code for 2D arrays?
import Cocoa
var str = "Hello, playground"
var arr = [[Int?]] ()
arr[1][2] = 17
print(str)