How to get safeAreaInsets in viewWillTransitionToSize (iPhone X)

I got the valid solution at Stackoverflow Japan.

It's just getting the insets in the UIViewControllerTransitionCoordinator.animate(alongsideTransition:completion:) closure like below:

override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
    super.viewWillTransition(to: size, with: coordinator)

    coordinator.animate(alongsideTransition: { (context) in
        ...

        let insets = ...safeAreaInsets

        ...
    }, completion: nil)
}