php5 to php7 migration code problem using odd OOP references? [duplicate] - php

Question

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Variable variables in classes using PHP 7
(2 answers)
Closed 1 year ago.
I'm trying to fix a friend's web site that needs to be updated to run on php7.2. It works fine on php5 but appears to crash with no errors when executing a command like this:
$$mod_name = &$$parent_array[$mod_parent]->addItem(new XNode($mod_name,$mod_url,"Images/doc.gif",false));
The weird variable reference like &$$ is not something I've seen before. Has this notation been depreciated in php7?
The code is using a library called xPandMenu. Here is the library:
https://www.phpclasses.org/package/2018-PHP-Generate-a-dynamic-hierarchic-menu.html
I reached out to the author of this code and he's not interested in updating it, and doesn't work with PHP much any more. I am not familiar with OOP and the odd variable/class references used.
Does anybody know what would cause this code to work fine in php5, but crash without error in php 7.2?

Answer 1

Here is the solution to this.
The way PHP7 parses double variable references is now different, according to this page:
https://www.php.net/manual/en/migration70.incompatible.php
So the proper re-writing of this:
&$$parent_array[$mod_parent]->addItem(new XNode($mod_name,$mod_url,"Images/doc.gif",false));
is:
&${$parent_array[$mod_parent]}->addItem(new XNode($mod_name,$mod_url,"Images/doc.gif",false));
Likewise a reference such as this in PHP5:
$$var['key'];
Behaves differently under PHP7 and must be hard-noted as this:
${$var['key']};