Robert Ames (.com!)

Upgrading from PHP4 to PHP5

So, I’ve spent some time upgrading the darwingames.com codebase to be PHP5 compatible. For those considering the transition (and language designers who are considering an incompatible source version upgrade), I offer the following observations.

The Good:

Relatively few files and/or lines needed to be changed. The major “classes” of changes were:

• class var => class public/private/protected
  This is a straightforward change due to the new scoping capabilities of PHP5. For bulk changes like this, making the scope public will match the default behaviour of var in PHP4.

• cannot modify $this
  We had used the idiom of:
  $game = new GAME();
$game->load( $id );
  …which modified this:
  $this = unserialize( getData($id) );
  Now that static functions are available, it’s simply easier to use the factory-method idiom as they recommend.
  $game = GAME::fetchGame( $id );

• static methods
  I know that you could previously call methods via MyClass::myFunction();, but now that it feels more officially supported, it gives you more options and makes PHP feel more like a “real” language (that and: funcResult()->objectMethod(); call support!).

• random =& stuff
  Now that objects are passed by reference by default, most usages of =& and &function foo() {...} are unnecessary.

The Bad:

Most of the “PHP5 changes” taken individually really do make it a better language. However, there are some significant problems and barriers faced by PHP5 due to some of the decisions the implementors have made (remember, this is from a user’s/programmer’s perspective).

• E_STRICT
  I program with E_STRICT. No if’s, and’s, or but’s. PHP5 (or any PHP) with E_STRICT is nice because it can catch a lot of silly “-ism’s”, misspellings, bad habits, etc. That’s not the problem, the problem is how it interacts with existing PHP4 code and the PHP5 language changes…

• var => public/private/protected
  I know I said this was a good change above, but in the context of PHP4 and PHP5-E_STRICT, any existing class with var keywords (ie: every single PHP4 class) will not run on PHP5 using E_STRICT without changes. Ok, no big deal, but that leads us to the next point…

• PEAR and/or other third-party libraries
  Meaning that every library or third-party library must make a choice between being PHP4-compatible or PHP5-compatible. That’s a fork, and it’s pretty difficult to maintain something that’s both PHP4 and PHP5 compatible, dealing with STRICT-mode in both versions. Furthermore that’s a decision that’s tough for a project or module to make (support 85% of existing installs or go for the “new-hotness”), and it’s not a decision that is easy for you (an individual) to make yourself. Message to PEAR. Fork now. Pour all resources into the new-hotness (PHP5) and freeze features in PHP4 versions of the libraries.

• is_a() vs. instanceof
  Ok, so you remove function is_a() and make it operator: instanceof, life is good, less things to bugfix, etc. But WHY do you make instanceof not take a string as a paramter (only a $variable or actual class reference). I guess a minor issue in the long-term, but really annoying in the short-term.

So, when designing incompatible language changes let me offer this advice:

• Take into account third-party libraries, they have 99% more code available than the average coder will write in their lifetime.

• Have a transition plan in place (that takes into account third-party libraries)… ie: run E_ALL - E_STRICT for six-months, update silly syntax-changes, and then switch over after now() + $SIX_MONTHS.

• Consider an E_PHP4_STRICT / E_PHP5_STRICT (or more generically: E_ALL_STRICT, E_COMPATIBLE_STRICT) to make maintaining PHP4/PHP5 code-bases easier what also might be nice is to do something like E_STRICT_ONLY_ON_NON_INCLUDED_FILES, as I’m perfectly OK with errors in included files, but I’d like to tag my own code as ‘needing to be strict’.

Having only browsed through the PHP codebase a few times in my years of using PHP, I am totally unqualified to make sure these recommendations are feasible, but from a user of the language’s perspective, they’d be items I’d appreciate (and if this experience report helps you in your PHP4-PHP5 transition, I’m glad :^).

22:46 CST | category / entries
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