@dynamicMemberLookup example

HexColor.swift

// An (useless) example of Swift 4.2 @dynamicMemberLookup attributes.
// let color1 = HexColor().cbcbcb
// let color2 = HexColor().000000 // This can also be built. Will be treat as "000000"

import Foundation

@dynamicMemberLookup
struct HexColor {
    subscript(dynamicMember member: String) -> UIColor? {
        do {
            let regex = try NSRegularExpression(pattern: "^([A-Fa-f0-9]{6}|[A-Fa-f0-9]{8})$", options: [])

            let results = regex.matches(in: member, options: [], range: NSRange(member.startIndex..., in: member))

            guard let hexString = results.map ({ (member as NSString).substring(with: $0.range) }).first else {
                return nil
            }

            var hexValue: UInt32 = 0
            guard Scanner(string: hexString).scanHexInt32(&hexValue) else {
                return nil
            }

            switch hexString.count {
            case 6:
                return UIColor(hex6: hexValue)
            case 8:
                return UIColor(hex8: hexValue)
            default:
                return nil
            }
        } catch {
            return nil
        }
    }
}

// Copied and modified from https://github.com/yeahdongcn/UIColor-Hex-Swift/blob/master/HEXColor/UIColorExtension.swift
extension UIColor {
    convenience init(hex6: UInt32, alpha: CGFloat = 1) {
        let red = CGFloat((hex6 & 0xFF0000) >> 16)
        let green = CGFloat((hex6 & 0x00FF00) >> 8)
        let blue = CGFloat( hex6 & 0x0000FF)
        let divisor: CGFloat = 255
        self.init(red: red / divisor,
                  green: green / divisor,
                  blue: blue / divisor,
                  alpha: alpha)
    }

    convenience init(hex8: UInt32) {
        let red = CGFloat((hex8 & 0xFF000000) >> 24)
        let green = CGFloat((hex8 & 0x00FF0000) >> 16)
        let blue = CGFloat((hex8 & 0x0000FF00) >> 8)
        let alpha = CGFloat(hex8 & 0x000000FF)
        let divisor: CGFloat = 255
        self.init(red: red / divisor,
                  green: green / divisor,
                  blue: blue / divisor,
                  alpha: alpha / divisor)
    }
}