Static typing

There is some renewed discussion about introducing static typing in PHP. I just read one very interesting post: The Safyness of Static Typing which I suggest everybody that is interested in this topic should read (and the links there). You may agree or disagree, but it is worth reading and even if you disagree it is worth ensuring you know the answers to the questions raised there, otherwise your disagreement lacks substance. I must admit I liked that post because it agreed with my feelings (not substantiated prior to that by any experimental data besides general experience I’ve acquired in the field) that type safety is not as close to silver bullet as some put it.

Within the context of PHP, I’m not sure if more strict typing (coercive typing is something in between and would require a bit different treatment) would be beneficial. I can see where it could be useful – i.e., for making JIT it probably would be very nice. On the other hand, Javascript has excellent JIT engines, as I have heard, without any additions of strict typing, so it’s not absolutely necessary. With PHP code living in runtime and static analysis tools not being routine part of mainstream development, at least as far as I have seen, I’m not sure addition of strict typing would help in any substantial way. Facebook guys, obviously, disagree – I wonder if they have some data to back it up, i.e. how that worked in practice and especially how “hybrid” model – i.e. having typed and untyped code coexist (that as I understand is what is happening, may be I am wrong here) works out and if it indeed provides better safety and reduced development time?

P.S. oh, and if you want a surefire way to annoy me, please call strict typing “type hinting”. I’m sure in the history of PHP there were examples of worse terminology (“safe mode” comes to mind as one) but that does not excuse this most unfortunate decision to name strictly typed arguments “hinting”.

hiphop for php

By now probably everybody that is connected to PHP world knows about Facebook’s HipHop.
So here are my thoughts about it.

1. This is a very cool and exciting technology. There were multiple attempts to do this in various ways, and from what it looks, HipHop is the most successful and appealing. I know doing these things is not easy – I tried something like that myself somewhere back in 2006 but was unable to go past very basic examples (I also made a mistake of choosing C instead of C++ as target, which I now think was not a smart decision). And the progress and support for almost all of the PHP magic is definitely great. There still are unsupported areas, but mostly are dark corners into which not many people venture (or should venture, at least 🙂

2. I do not see it as a replacement for php.net code or Zend Engine. The mainstream of PHP development still happens in the community around php.net and I do not think it is going to change anytime soon. I also see the fact that HipHop engine basically re-implements all the extensions as a serious disadvantage, for which the solution should be sought, even though I completely understand the technical reasons for doing so. I do not know which kind of the solution but while for the company like Facebook it might be OK to “freeze” certain set of extensions and features and maybe catch up periodically, I think it is obvious how such model can be a problem for the wider adoption.

3. If we talk about broader adoption of this technology in a wider PHP world, there are some serious challenges to consider:

• Plugins: right now, you must compile your whole application. However, many real-life applications have extensive plugin models, which consist of their main competitive advantage – take WordPress, Drupal, Magento, any Zend Framework app – all of these allow to write custom plugins and run them alongside the main code base. The model in which you have to rebuild whole application each time you add/change a line of code is not acceptable in these circumstances.
• Modularity: this is connected to the above, but is a bit different. PHP right now runs on Apache, IIS, Lighty, nginx, and tons of other servers in different environments. For the use of the technology in the wide variety of environments PHP is used in, one must be able to modularize  and separate the application PHP code from the runtime and the environment.
• Portability: I tried to run a bunch of my scripts through the demo that the HipHop team was very kind to give me – and most of them experiences unsupported functions or some function didn’t work exactly as their PHP counterparts (random example: PHP’s fopen() would error out given empty first argument, while HPHP implementation would open the current directory as file. There are more such things…). Now, I admit, it would be very easy to fix them, to use different functions and they would work, but again I think it’s obvious how it can be a problem for a PHP programmer, if you are not coding targeting HipHop specifically – and especially of you use 3rd-party code. Having different implementations always presents portability challenges.
• Thread-safety: A huge problem with PHP thread-safety is third-party libraries. Many of them are not thread safe either explicitly, or, even worse, implicitly – i.e. they just have either bugs or information leaks between threads (like changing some setting in one thread and feeling its effect in another – imagine chdir() leaking through the thread boundaries – see how it can be a problem?) HipHop team’s answer to this question was “we had fixed all those extensions” – which, without diminishing the capabilities of this excellent team, I think is not a satisfactory answer. It very well may be that they indeed fixed all the problems they could see in the code they run – but let us not forget they run one (albeit huge) application. I have hard time believing they have fixed every threading problem with every C library in existence that has interface to PHP and will continue to do so as long as C libraries exist. This of course goes back to modularity question, since here we have coupling between compiling and runtime model.
• Debugging: obviously, debugging C++ code is orders of magnitude harder than PHP code. So you either need ninja debugging skills, or a very good set of tools to allow you to identify a problem in a live server running non-source PHP.

4. I also see certain danger potential in the success of this project. The danger primary being that the performance is very important in the web world, and it can give an incentive to the PHP community to change PHP in ways that may be better for performance, but would make PHP into being an entirely different language. The obvious example of this is strict typing – strict typing, of course, would help the compiler a lot in figuring out what’s going on with the code. However, I am not convinced at all that it would make the life of a PHP programmer easier. I know there are a number of proponents of this but I am still not convinced it’s the way for PHP to go. And there might be other incentives like this – i.e. to add or drop features to PHP, or avoid using certain constructs and features, for the sole reason of making it more compile-able. Now, there’s nothing wrong with being compiler-friendly, but I don’t think for a language like PHP it should be the primary motivation.

Re-reading these notes I realized some of it might give an impression that I dislike the technology. It is absolutely not so – on the contrary, I think it is a great addition to the PHP world and I want again to congratulate the HipHop team on a huge achievement and thank them for making the PHP world better and more exciting. It would be very interesting to see how this develops and how and if the problems can be overcome and how this technology changes the PHP world and is changed by it.

duck operator

Crazy idea for today – operator to check conformance to specific interface without actually implementing it. Why one would want that?
Well, if you are into duck typing style of programming, it may be interesting for you to have an object that implements certain set of functions, but not necessary declares it at class definition. Languages like Smalltalk do it all day along, so why PHP couldn’t? The idea is it looks like this:

interface Cow {
  function moo();
  function eatGrass();
}
/* somewhere else */
class MooingGrassEater {
  function moo() {/*stuff */}
  function eatGrass() {/*stuff */}
  /*stuff */
}
/* somewhere else */
function CowConsumer($classname) {
$foo = new $classname();
if($foo implements Cow) {
  echo "Behold the cow:";
  $foo->eatGrass();
  $foo->moo();
} else {
  echo "$classname is not a cow!";
}

implements here is our duck operator. Note that unlike instanceof, no formal relationship is required, but only practical implementation. So another name would be “common law marriage operator” 😉

Of course, this one would be anathema to “strict OO” camp, so if you subscribe to that, just ignore this post 🙂

Two challenges to this idea are:

1. __call() – we have no way to know what __call does. So either we ignore it or say “ok, __call does everything”. I’d go for the latter.
2. Performance. To check duck implementation one basically would have to match method lists, which amounts to number of is_callable calls equal to the number of methods in interface being checked.

Actually, PHP uses this style sometimes – see, for example, user defined streams. But there’s no nice way to work with it from the consumer side.