test.php

<?php

class Test {
  private $number = 0;
  private $sub;

  public function __construct($n) {
    $this->number = $n;
    $this->sub = new SubTest($n, $this);
    echo "construct ".$this->number."\n";
  }

  public function release_childen() {
    unset($this->sub);
  }

  public function __destruct() {
    unset($this->sub);
    echo "destruct ".$this->number."\n";
  }
}

class SubTest {
  private $number = 0;
  private $parent;
  public function __construct($n, $parent) {
    $this->number = $n;
    $this->parent = $parent;
    echo "subtest construct ".$this->number."\n";
  }
  public function __destruct() {
    echo "subtest destruct ".$this->number."\n";
  }
}

$a = new Test(1);
$a->__destruct();
//$a->release_childen();
$a = new Test(2);
echo "--- end of script ---\n";
?>