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/* ---------------------------------------------- */
/*  Default Display Name as First Name Last Name
/* ---------------------------------------------- */

/**
 * New user registrations should have display_name set to 'firstname lastname'
 * Best used on 'user_register'
 * @param string $name 
 * @return $name
 * @uses pre_user_display_name()\
 */

add_filter('pre_user_display_name', 'default_display_name');

function default_display_name($name) {
  if ( isset( $_POST['billing_first_name'] ) ) {
    $firstname = sanitize_text_field( $_POST['billing_first_name'] );
  }
  if ( isset( $_POST['billing_last_name'] ) ) {
    $lastname = sanitize_text_field( $_POST['billing_last_name'] );
  }
  $name = $firstname . ' ' . $lastname;
  return $name;
}