hiddenKeyPath.swift

import UIKit

let keyPath = "continuous" + "Corners"

extension CALayer {
    var infiniteCorners: Bool {
        get { return value(forKeyPath: keyPath) as! Bool }
        set { setValue(newValue, forKeyPath: keyPath) }
    }
}

You should definitely add a resendsToSelector-check in case something changes. You have no guarantee that SPI stays the same.

responds(to: Selector(("setContinuousCorners:")))