Description:
------------
    $data = [1,2,3];
    foreach ($data as &$value)
    {
    }
    foreach($data as $value)
    {
    }
var_dump($data);
在第二次foreach之后，通过xdebug打印的data显示结果：
data: (refcount=1, is_ref=0)=array (0 => (refcount=1, is_ref=0)=1, 1 => (refcount=1, is_ref=0)=2, 2 => (refcount=2, is_ref=1)=2)


Test script:
---------------
    $data = [1,2,3];
    foreach ($data as &$value)
    {
    }
    foreach($data as $value)
    {
    }
var_dump($data);


Expected result:
----------------
array(3) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
}

Actual result:
--------------
array(3) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  &int(2)
}