PHP 中的引用赋值运算符

<?php
    $test = array();
    $test1 =& $test['z'];
    var_dump($test);
?>

array(1) {
  ["z"]=>
  &NULL
}

<?php
    $firstValue=100;
    $secondValue =& $firstValue;
    echo "First Value=".$firstValue."<br>";
    echo "Second Value=". $secondValue."<br>";
    $firstValue = 45000;
    echo "After changing the value of firstValue, secondValue will reflect the firstValue  because of =&","<br>";
    echo "First Value=". $firstValue."<br>";
    echo "Second Value=". $secondValue;
?>

First Value=100
Second Value=100
After changing the value of firstValue, secondValue will reflect the firstValue  because of =&
First Value=45000
Second Value=45000

<?php
    $second = 50;
    $first =& $second;
    $third =& $second;
    $fourth =& $first;
    $fifth =& $third;
    // $first, $second, $third, $fourth, and $fifth now all point to the same data, interchangeably
    //should print 50
    echo $fifth;
?>

50

<?php
    $second = 50;
    $sixth = 70;
    $first =& $second;
    $third =& $second;
    $fourth =& $first;
    $fifth =& $third;
    // $first, $second, $third, $fourth, and $fifth now all point to the same data, interchangeably
    //unlink $fourth from our link, now $fourth is linked to $sixth and not $third
    $fourth = $sixth;
    echo $fourth;
?>

70