sorting - Sort an array of optional items that holds yet another optional

Question

How can I sort an array of optionals that holds an optional NSdate?

class HistoryItem {
   var dateCompleted: NSDate?
}

let firstListObject = someListOfObject.last
let secondListObject = someOtherListOfObject.last
let thirdListObject = evenSomeOtherListOfObject.last //Last returns 'T?'

var array = [firstListObject , secondListObject, thirdListObject]

How can I sort array based on dateCompleted?

Answer 1

Your sort function could use a combination of optional chaining and the nil coalescing operator:

sort(&array) {
    (item1, item2) -> Bool in
    let t1 = item1?.dateCompleted ?? NSDate.distantPast() as! NSDate
    let t2 = item2?.dateCompleted ?? NSDate.distantPast() as! NSDate
    return t1.compare(t2) == NSComparisonResult.OrderedAscending
}

This would sort the items on the dateCompleted value, and all items that are nil and items with dateCompleted == nil are treated as "in the distant past" so that they are ordered before all other items.

---

Update for Swift 3 (assuming that dateCompleted is a Date):

array.sort { (item1, item2) -> Bool in
    let t1 = item1?.dateCompleted ?? Date.distantPast
    let t2 = item2?.dateCompleted ?? Date.distantPast
    return t1 < t2
}