unserialize_tostring.php

<?php
class Foo {
  public $value = 'abc';

  public function __toString() {
    echo(__METHOD__).PHP_EOL;
    return '';
  }
}

function func($text) {
  echo('func start').PHP_EOL;

  $a = unserialize($text);
  $a .= '.txt'; // not string

  echo('func end').PHP_EOL;
}

func('O:3:"Foo":1:{s:5:"valua";s:3:"abc";}');