gistfile1.php

<?php

class A {
  public $id;
  
  public function __construct($id){
    $this->id = $id;
  }
}

$a = new A(10);

print '$a->id = '. $a->id .'<br />';

$b = new A(12);

print '$b->id = '. $b->id .'<br />';

$b = $a;

print 'After: $b->id = '. $b->id .'<br />';

$b->id = 15;

print 'After: $b->id = '. $b->id .'<br />';
print 'After: $a->id = '. $a->id .'<br />';

?>