实际上这两种方法都是有效的，但这取决于你的需求。通过引用传递值通常会使脚本变慢。因此，考虑到执行时间，最好按值传递变量。此外，当按值传递变量时，代码流更加一致。

在PHP 5中通过引用传递对象，在PHP 4中通过值传递对象。 默认情况下，变量是按值传递的!

阅读此处:http://www.webeks.net/programming/php/ampersand-operator-used-for-assigning-reference.html

取决于版本，4是值，5是引用。

实际上这两种方法都是有效的，但这取决于你的需求。通过引用传递值通常会使脚本变慢。因此，考虑到执行时间，最好按值传递变量。此外，当按值传递变量时，代码流更加一致。

可以通过引用将变量传递给函数。这个函数将能够修改原始变量。

你可以在函数定义中通过引用来定义段落:

<?php
function changeValue(&$var)
{
    $var++;
}

$result=5;
changeValue($result);

echo $result; // $result is 6 here
?>

http://www.php.net/manual/en/migration5.oop.php

In PHP 5 there is a new Object Model. PHP's handling of objects has been completely rewritten, allowing for better performance and more features. In previous versions of PHP, objects were handled like primitive types (for instance integers and strings). The drawback of this method was that semantically the whole object was copied when a variable was assigned, or passed as a parameter to a method. In the new approach, objects are referenced by handle, and not by value (one can think of a handle as an object's identifier).