zeroAllocNearestCommonAncestor.swift

public extension UIView {
   public func nearestCommonAncestor(with otherView: UIView) -> UIView? {
      let myHierarchyDepth = sequence(first: self, next: { $0.superview }).reduce(0) { (count, view) in count + 1 }
      let otherHierarchyDepth = sequence(first: otherView, next: { $0.superview }).reduce(0) { (count, view) in count + 1 }
      var longest = sequence(first: myHierarchyDepth < otherHierarchyDepth ? otherView : self, next: { $0.superview })
      var shortest = sequence(first: myHierarchyDepth < otherHierarchyDepth ? self : otherView, next: { $0.superview })
      return zip(
         longest.dropFirst(abs(myHierarchyDepth - otherHierarchyDepth)),
         shortest
      ).first(where: { $0.0 === $0.1 })?.0
   }
}