PHP Script to Create a unique alphanumeric string like Voucher Code, Referral Code, Coupon Code, OTP or any kind of Promotional Code

uniquable.php

<?php

/**
 *
 */
trait Uniquable
{
  // this function can create a unique alphanumeric string. To create a
  // unique string contains letter and number (alphanumeric) with the character limit $limit. These kinds of
  // unique string can be used as Voucher Code, Referral Code, Coupon Code, OTP or any kind of Promotional Code.
  //
  // In the above function, I’m using the default PHP functions.
  // base_convert – Convert a number between arbitrary bases.
  // sha1 – Calculate the sha1 hash of a string.
  // uniqid – Generate a unique ID.
  // mt_rand – Generate a random value via the Mersenne Twister Random Number Generator.
  function unique_code($limit)
  {
    return substr(base_convert(sha1(uniqid(mt_rand())), 16, 36), 0, $limit);
  }
}