Open Radar

 
Summary:
Use of a temporary variable in a class's description computed property seems to make Playgrounds go wild, iterating forever.

Steps to Reproduce:
1. Download attached LinkedList.playground
2. Open it in Xcode 8.2.1 on El Capitan
3. Watch it run
4. Uncomment the "This iterates forever" code that is currently commented out, and comment out the "This works" code.

Expected Results:
Description should be executed just as before since the two code blocks are functionally identical.

Actual Results:
Playground starts iterating forever.

Version:
Xcode 8.2.1

Notes:

Configuration:
El Capitan 10.11.6 with latest updates.


Playground contents follow:

//: Playground - noun: a place where people can play

class LinkedList: CustomStringConvertible {
	var next: LinkedList?
	let data: Int
	
	init(next: LinkedList?, data: Int) {
		self.next = next
		self.data = data
	}
	
	var description: String {
		var result = "\(data)"

		// This works
		if next != nil {
			result += ", \(next!.data)"
		}
		// This iterates forever
		/*let i: LinkedList? = next
		if i != nil {
			result += ", \(i!.data)"
		}*/
		
		return result
	}
}


func linkedListFromArray(_ array: [Int]) -> LinkedList? {
	var head, tail: LinkedList?
	
	for data in array {
		let temp = LinkedList(next: nil, data: data)
		
		if head == nil {
			head = temp
		}

		tail?.next = temp
		tail = temp
	}
	
	return head
}

let linkedList1 = linkedListFromArray([10, 9, 8, 7, 6, 5, 4, 3, 2, 1])
let linkedList2 = linkedListFromArray([])
let linkedList3 = linkedListFromArray([1])