Swift create array of type with dynamic type reference without generics

Question

Given this function:

func createEmptyArrayWithViewType(viewType: UIView.Type) -> [UIView] {
    /// Create array of viewType views
}

How do I create an empty array with that function? viewType parameter can be any UIView subclass (UIImageView, UILabel, etc.) Is it possible without using generics?

UPDATE

Ok I think some more context would help.

What I am trying to build is a reuse queue that pretty much does what UITableView and UICollectionView provide.

This is my class's current code:

class SwipeView: UIView {
  private var _reuseQueues = [String: [MatchSwipeCell]]()

  ...
}


/// -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
//MARK: - Reuse queue
/// -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
extension SwipeView {
  func registerClass(cellClass: SwipeCell.Type, forCellWithReuseIdentifier identifier: String) {
    if let reuseQueue = _reuseQueues[identifier] {
      fatalError("Reuse identifier '\(identifier)' was already registered with class '\(reuseQueue.dynamicType.Element.self)'")
    }

    /// This is not working!
    _reuseQueues[identifier] = [cellClass]()
  }

  func dequeueReusableCellWithReuseIdentifier(identifier: String) -> SwipeCell {
    guard var reuseQueue = _reuseQueues[identifier] else {
      fatalError("No class was registered for the reuse identifier '\(identifier)'")
    }

    if let cell = reuseQueue.first {
      reuseQueue.removeFirst()
      cell.prepareForReuse()
      return cell
    }

    return reuseQueue.dynamicType.Element(reuseIdentifier: identifier)
  }

  private func enqueueCellForReuse(cell: SwipeCell) {
    _reuseQueues[cell.reuseIdentifier]?.append(cell)
  }
}

I think that using a switch statement on the view type in your function is the only way to do it. — AlexB
– AlexB, Commented Jan 2, 2016 at 17:01
Is there any reason you are trying to build something generic without generics? I do not see the use case for what you are asking for! — luk2302
– luk2302, Commented Jan 2, 2016 at 17:09
it's very simple. Just use return Array<UIView>() Since the return isn't generic it doesn't matter what subclass you enter as a param. There is no way/need/reason to specialise it in any way, since the return would undo all that. — R Menke
– R Menke, Commented Jan 2, 2016 at 17:15
in a UITableView it also just uses UITableViewCell instead of specific subclasses. You still have to downcast them. Just use the same method. — R Menke
– R Menke, Commented Jan 2, 2016 at 18:17

kostek · Accepted Answer · 2016-01-02 17:24:15Z

1

Wait, you merely want to create an empty array of UIViews? Your function would then look like this:

func createEmptyArrayWithViewType(viewType: UIView.Type) -> [UIView] {
    return []
}

viewType parameter is not needed. You can put into this array any view that you want (UIImageView, UILabel, etc.)

var array = createEmptyArrayWithViewType(UIImageView)
array.append(UIImageView())
array.append(UILabel())

If you want to have you function return [UIView] you just end up with empty array of UIViews

answered Jan 2, 2016 at 17:24

kostek

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