Function that contains common validations for a textfield

CommonTextfieldValidations.swift

//
//  CommonTextfieldValidations.swift
//
//  Created by Rigoberto Sáenz Imbacuán (https://www.linkedin.com/in/rsaenzi/)
//  Copyright © 2019. All rights reserved.
//

extension MyViewController: UITextFieldDelegate {
    
    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        
        // Deletion is enabled
        if string.count == 0 {
            return true
        }
        
        // Only numbers are permitted
        guard string.rangeOfCharacter(from: CharacterSet.decimalDigits.inverted) == nil else {
            return false
        }
        
        // Max digits allowed
        let fullLength: Int = textField.text!.count + string.count
        if fullLength > 10 {
            return false
        }
        
        return true
    }
}