import UIKit import CommonCore final class VisibilityTrackingCardView: UIView, VisibleBoundsTrackingContainer { var blockView: VisibleBoundsTrackingView? { didSet { oldValue?.removeFromSuperview() blockView.map { addSubview($0) } } } var visibleBoundsTrackingSubviews: [VisibleBoundsTrackingView] { blockView.asArray() } }