Gist for https://rymc.io/2018/12/03/swipeable-nscollectionview/

nscollectionviewitem-setup.swift

class HolidayCalendarCollectionViewItem: NSCollectionViewItem {
    var leftAnchor: NSLayoutConstraint?
    var initialTouchOne: NSTouch?
    var initialTouchTwo: NSTouch?
    var currentTouchOne: NSTouch?
    var currentTouchTwo: NSTouch?
    var initialPoint: CGPoint?
    var isTracking = false

    public lazy var contentView: NSView = {
        let view = NSView(frame: .zero)
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()

    override func loadView() {
        let itemView = NSView(frame: .zero)
        itemView.postsFrameChangedNotifications = false
        itemView.postsBoundsChangedNotifications = false
        itemView.wantsLayer = true
        itemView.allowedTouchTypes = [.direct, .indirect]
        itemView.addSubview(contentView)
        
        leftAnchor = contentView.leftAnchor.constraint(equalTo: itemView.leftAnchor)
        NSLayoutConstraint.activate([
            contentView.topAnchor.constraint(equalTo: itemView.topAnchor),
            leftAnchor!,
            contentView.bottomAnchor.constraint(equalTo: itemView.bottomAnchor),
            contentView.widthAnchor.constraint(equalTo: itemView.widthAnchor),
        ])
        
        view = itemView
    }
}