Let you set UITextField max length in storyboard or xib

textFieldMaxLength.swift

// Set textfield max length
private var __maxLengths = [UITextField: Int]()
extension UITextField {
    @IBInspectable var maxLength: Int {
        get {
            guard let l = __maxLengths[self] else {
                return Int.max // (global default-limit. or just, Int.max)
            }
            return l
        }
        set {
            __maxLengths[self] = newValue
            addTarget(self, action: #selector(fix), for: .editingChanged)
        }
    }

    @objc func fix(textField: UITextField) {
        let t = textField.text
        textField.text = t?.safelyLimitedTo(length: maxLength)
    }
}

extension String {
    func safelyLimitedTo(length n: Int) -> String {
        let c = self
        if c.count <= n { return self }
        return String(Array(c).prefix(upTo: n))
    }
}