Hello! When opened viewController is closed, and the caller viewController appears, I iterate through the data that the called viewController modified. And here's the strange part - I can't iterate through the classes in the array, for some reason, even though the conditions for while = true are met - Swift runtime refuses to enter inside while loop. I've tryed to emulate this situation in playground - there it works just fine. Is it bug in Swift, or some multighreading stuff ? Please help ? Code is: https://github.com/afirthes/Numberator UPDATE: It was some xcode debug caching error, after restart it worked fine.