ASLabel.swift

extension NSAttributedString {
    func size(forWidth width: CGFloat) -> CGSize {
        return boundingRect(
            with: CGSize(width: width, height: CGFloat.greatestFiniteMagnitude),
            options: [.usesLineFragmentOrigin, .usesFontLeading],
            context: nil
        ).size
    }   
}

class ASLabel: UIView {

    override var intrinsicContentSize: CGSize {
        return attributedText?.size(forWidth: bounds.width) ?? .zero
    }

    override func layoutSubviews() {
        super.layoutSubviews()

        if savedBounds == nil || savedBounds != bounds {
            invalidateIntrinsicContentSize()
        }

        savedBounds = bounds
    }

    private var savedBounds: CGRect?

    ...

}