A UILabel subclass that can hold attributes and apply them to text

Label.swift

import UIKit
/// A UILabel subclass that can hold attributes and apply them to text
@IBDesignable
final class Label: UILabel {
    convenience init(attributes: [NSAttributedStringKey: Any]) {
        self.init()
        self.attributes = attributes
    }

    // MARK: Properties
    /// The attributes for the attributed string.
    var attributes: [NSAttributedStringKey: Any] = [:] {
        didSet {
            guard let existingString = super.attributedText?.string else { return }
            super.attributedText = NSAttributedString(string: existingString, attributes: attributes)
        }
    }
    /// The current text that is displayed by the label.
    override var text: String? {
        set { super.attributedText = NSAttributedString(string: newValue ?? "", attributes: attributes) }
        get { return super.attributedText?.string }
    }
    /// The font used to display the text.
    override var font: UIFont! {
        get { return attributes[.font] as? UIFont ?? .systemFont(ofSize: 17) }
        set { attributes[.font] = newValue }
    }
    /// The color of the text.
    override var textColor: UIColor! {
        get { return attributes[.foregroundColor] as? UIColor ?? .black }
        set { attributes[.foregroundColor] = newValue }
    }
    /// The text alignment of the receiver.
    override var textAlignment: NSTextAlignment {
        get { return paragraphStyle?.alignment ?? .natural }
        set { setParagraphValue(newValue, for: \.alignment) }
    }
    /// The mode that should be used to break lines in the receiver.
    override var lineBreakMode: NSLineBreakMode {
        get { return paragraphStyle?.lineBreakMode ?? .byWordWrapping }
        set { setParagraphValue(newValue, for: \.lineBreakMode) }
    }
    /// The distance in points between the bottom of one line fragment and the top of the next.
    var lineSpacing: CGFloat {
        get { return paragraphStyle?.lineSpacing ?? 0.0 }
        set { setParagraphValue(newValue, for: \.lineSpacing) }
    }
    /// The receiver’s minimum height.
    @IBInspectable
    var minimumLineHeight: CGFloat {
        get { return paragraphStyle?.minimumLineHeight ?? 0 }
        set { setParagraphValue(newValue, for: \.minimumLineHeight) }
    }
    /// The receiver’s maximum height.
    @IBInspectable
    var maximumLineHeight: CGFloat {
        get { return paragraphStyle?.maximumLineHeight ?? 0 }
        set { setParagraphValue(newValue, for: \.maximumLineHeight) }
    }
    /// The natural line height of the receiver is multiplied by this factor (if positive) before being constrained by minimum and maximum line height.
    @IBInspectable
    var lineHeightMultiple: CGFloat {
        get { return paragraphStyle?.lineHeightMultiple ?? 0 }
        set { setParagraphValue(newValue, for: \.lineHeightMultiple) }
    }
    /// This value specifies the number of points by which to adjust kern-pair characters.
    @IBInspectable
    var kern: CGFloat {
        get { return attributes[.kern] as? CGFloat ?? 0 }
        set { attributes[.kern] = newValue }
    }
    // MARK: Private
    private var paragraphStyle: NSMutableParagraphStyle? {
        return attributes[.paragraphStyle] as? NSMutableParagraphStyle
    }
    /// Sets a value at the specified KeyPath of ParagraphStyle.
    private func setParagraphValue<T>(_ value: T, for keyPath: ReferenceWritableKeyPath<NSMutableParagraphStyle, T>) {
        let style = paragraphStyle ?? NSMutableParagraphStyle()
        style[keyPath: keyPath] = value
        attributes[.paragraphStyle] = style
    }
    // MARK: Unavailable
    @available(*, unavailable)
    override var attributedText: NSAttributedString? { willSet { } }
}