This document is http://tnx.nl/php5 - If you replicate it, please do link. Trust HTTP headers for last-modified info. Corrections and additions are welcome at geeks#@tnx.nl.

Existing problems not addressed

Yes, some bugs were fixed in PHP 5, but none of the issues described in http://tnx.nl/php was addressed. PHP is still a world of inconsistency, still lacks advanced scoping, still has a bloated core, etcetera.

The rest of this document will be a discussion of the language changes in http://www.php.net/zend-engine-2.php. Again, it will mainly be a comparison with Perl. In general, this means that you'll be told that Perl already had the feature ages ago :)

Oh, please note that I am not an OO expert and will not claim that anything is or is not "pure OO".

New Object Model

PHP has a new object model. This is the first really useful incarnation of object orientation in PHP. Without doubt, the changes made are very valuable to PHP and were all inspired by the needs of PHP coders.

There is a big philosophical difference between PHP and Perl, that makes the object models hard to compare. In Perl, the object model is extremely flexible and simple, and doesn't force the user into any mindset. It does not have special syntax, but re-uses other parts of the language. A class is just a package, a method is just a sub, an object is just a reference to a blessed data structure.

Private and Protected Members/Methods

PHP 5 introduces the private and protected keywords. Perl does not have these. It also doesn't have any keywords that are equivalent. That does not mean that there is no equivalent. Perl lets you check these things yourself with the caller operator, which returns information about the calling context.

In general, private and protected things are rare in Perl. Many Perl coders believe in freedom, and only prefix an underscore as a visual indication. The perlmodlib document says:

Perl does not enforce private and public parts of its modules as you may have been used to in other languages like C++, Ada, or Modula-17. Perl doesn't have an infatuation with enforced privacy. It would prefer that you stayed out of its living room because you weren't invited, not because it has a shotgun.

Because some masochists do like painting themselves into a corner, Perl 6 will support these features.

Abstract Classes and Methods, Interfaces

In Perl, you create these yourself. Nothing special. It should be noted that Perl supports multiple inheritance, while PHP does not. There are those who think multiple inheritance is evil, and there are those who know it can be a useful tool in some situations. Perl does not limit the people who think it's useful.

Perl 6 will have special syntax for these features.

Class Type Hints

Perl has no types, period. However, an object's class can be checked manually.

I find it strange that although PHP does have types, this mechanism cannot be used to test built-in types.

Perl 6 will have types and subroutine signatures.


PHP lets you block inheritance. Perl does not provide this option at all.

Larry Wall says in Apocalypse 12:

Some languages solve this (or think they solve it) by letting classes declare themselves to be closed and/or final. But that's actually a bad violation of OO principles. It should be the users of a class that decide such things--and decide it for themselves, not for others. As such, there has to be a consensus among all users of a class to close or finalize it. And as we all know, consensus is difficult to achieve.

Still, because the Perl wants to let people free in how they code, Perl 6 will support this feature.

Object Cloning

A PHP object can now be cloned. Not with $object->clone, as I would have expected, but with clone $object.

Perl has real references, and objects are just data structures. Because circular references are possible, and perl cannot tell if a certain data structure is part of the object, it cannot provide a default cloning method. A class has to provide one.

PHP has just taken another step towards never being able to support real references.

Unified Constructors

This is just a philosophy change. Perl has a different philosophy than PHP 4 and PHP 5.


PHP finally has destructors. Perl has had destructors for a very long time. Now if only PHP had lexical scope, the destructors would be really useful! But alas, it doesn't sport such classy extras. Instead, only explicit destruction and destruction at the end of the function or script exist.


PHP now has constants in classes. Nothing special, and something that Perl coders usually laugh about: why are classes so different from "normal" code?


Perl has had exception handling all along, but with unusual syntax. Throwing an exception is done with die, catching it is done with eval { ... } (which is neither slow nor dangerous) and if ($@) { ... }. And for those who want very complex exception mechanisms, there are several extensions available from CPAN.

Dereferencing objects returned from functions

Believe it or not, in PHP 4, it was impossible to call a method on a returned object. That also made it impossible to stack methods, and essentially made OO programming a pain in the ass. Again, Perl coders laughed: why make OO programming different from the rest of the language, if you can merge the two and get all features for free?

Static Methods

Because in Perl a method is just a sub that gets passed one extra argument, calling methods from outside object oriented context has always been possible.


In Perl, this is called isa and it has been around for a very long time. (Read it as is-a.) I find it funny that PHP has this as an infix operator, instead of using object oriented syntax. Can the internals of PHP still not really handle OO?

PHP: if ($foo instanceof Bar) ...
Perl: if ($foo->isa('Bar')) ...

TODO: find out if the class has to be a literal (none of the PHP examples are like $foo instanceof $bar, while in Perl it is perfectly valid to say $foo->isa($bar).


This is not Perl's AUTOLOAD, but something that is called when a class that does not exist is used. In Perl, this has been possible for a long time, and there even is a module that automatically loads modules on demand using this mechanism.

Overloadable Method calls and Property accesses

Perl has many, many ways of doing this. But, I have to admit that in general I like how PHP does __get and __set better (just not the names).


Perl has several ways of letting an object be iterable

New __METHOD__ constant

Perl doesn't have this as a constant (partly because the method name isn't always known at compile time), but allows you to retrieve the current sub's name through caller.

New __toString() method

Hah, they call this magic! PHP lets the coder specify how their objects should be stringified, but provides no way of using it as an array or number.

Perl has a very sophisticated overloading mechanism that lets you overload an object differently in different contexts.

Reflection API

Perl has always been this flexible, just in a different way


Life has just been made much better for PHP programmers. But the real, lower level issues remain. Adding an object model doesn't fix the shortcomings that exist throughout the language.

And they still don't support real OO syntax for their built in objects like MySQL "resources".

PHP 5 isn't a BIG improvement. I wonder why it deserves a new major version number.