ios – Partially retaining the placeholder in UITextField

I’m making an attempt to attain beneath picture:

As you’ll be able to see within the picture, when a person varieties a quantity into the textfield, the opposite digits of the quantity nonetheless stand as a placeholder. (000 000 0000)

To do this, I positioned a UILabel within the UITextField.

var placeHolderLabelString = "___ ___ ____"
var placeholderLabel = UILabel()
placeholderLabel.textual content = placeHolderLabelString
placeholderLabel.sizeToFit()
numberInputView.addSubview(placeholderLabel)
placeholderLabel.textColor = .grey
placeholderLabel.font = numberInputView.font

I need to delete every underscore when a person varieties a digit into the textfield. I’ve tried the beneath code:

func textField(_ textField: UITextField, shouldChangeCharactersIn vary: NSRange, replacementString string: String) -> Bool {

    let rnd = Vary(vary, in: placeHolderLabelString)!
    placeHolderLabelString = placeHolderLabelString.replacingCharacters(in: rnd, with: " ")
    placeholderLabel.textual content = placeHolderLabelString

    return true
}

However this does not work. It provides an area char to the start of the placeHolderLabelString, not changing it. How can I try this?