leftColumnFrame.swift

private func leftColumnFrame(for availableSize: CGSize) -> CGRect {
    switch traitCollection.layoutDirection {
        case .unspecified, .leftToRight:
            return CGRect(x: 0.0, y: 0.0, width: leftColumnWidth, height: size.height)
        case .rightToLeft:
            return CGRect(x: size.width — leftColumnWidth, y: 0.0, width: leftColumnWidth, height: size.height)
    }
}