Behind The Code, with DrByte

This the 3rd in a series about readying your plugins for PHP 5.3, and for PHP 5.4, 5.5 and 5.6.

NOTE: This post assumes some pretty solid PHP knowledge, because all the changes listed will require adapting your code to find a new way to do whatever it was doing before.

NOTE: This is not the complete official list of changes. I've edited this list down to the basics, catering mostly to the topics that might affect people writing plugins for Zen Cart. For much more detailed lists of changes, see the official PHP documentation on migrating between PHP versions.



In PHP 7.0 the following functionality/features changed:
a) class constructors must be called __construct and not just be the same function name as the class anymore.
b) indirection - use of $$foo['bar']['baz'] needs to be rewritten as ${$foo['bar']['baz']} else it will be seen as ($$foo)['bar']['baz']. Also, $foo->$bar['baz'] has to be rewritten as $foo->{$bar['baz']} if that's what was intended.
c) switch() statements cannot have multiple "default:" blocks

In PHP 7.1 there were numerous changes, but few likely to impact regular Zen Cart use
PHP 7.1 is nearly identical to PHP 7.0 in terms of compatibility, but 7.1 is faster, so there's no point in using 7.0 if 7.1 is available to you!


For PHP 7.2 the following changes are required:
a) calls to each() are deprecated; use foreach() instead. See examples here: Refactor each() to foreach() for compatibility with PHP 7.2
b) create_function() is deprecated. Use anonymous functions ("Closures") instead.
c) The __autoload() mechanism is deprecated in favor of spl_autoload_register() instead.


For PHP 7.3 the only change found necessary in Zen Cart (over PHP 7.2 compatibility) was:
- using the "continue" statement inside a "switch" loop -- should be changed to "break"
- many "strict" conditions now trigger notices

Other notes about 7.3:
- calls to compact() with undefined variables will cause errors
- In case of troubleshooting rare problems that could be caused by the very few SPL autoloads in ZC, that any SPL Autoloads that fail will cause all subsequents to fail too, instead of just a warning in previous PHP versions.

For PHP 7.4 the only change found necessary in Zen Cart (over PHP 7.3 compatibility) was:
- a couple nested ternary operator calls needed extra parentheses for clarity

Other notes about 7.4:
- added Null coalescing assignment operator (??=)


On github I've posted a gist containing some regex patterns which can be used to identify incompatible old PHP code


PLEASE NOTE THE OFFICIAL PHP VERSION SUPPORT TIMELINE: http://php.net/supported-versions.php