排序可选项目的数组保存又一可选 [英] Sort an array of optional items that holds yet another optional

问题描述

我怎么能进行排序自选数组保存一个可选的NSDate？

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]

我如何可以排序基于dateCompleted阵列？

How can I sort array based on dateCompleted?

推荐答案

您的排序功能，可以使用另购的链接和零组合
合并运算符：

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
}

这将在 dateCompleted 值项的所有项目进行排序，并
是无和 dateCompleted ==零是在遥远的过去当作物品
使他们之前的所有其他项目进行排序。

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.

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