This has been discussed, and won't happen.  Runkit simply breaks too many of PHP's 
builtin (internal) assumptions.

I'm glad you like it though!

Umm what internal assumptions are broken if using runkit? And why is this so big of a problem? Also alternatively, it may be possible to extend the functionality of Reflection API so that the Reflection class does what runkit can do by adding/removing/copying methods to the target class. Heres what the user suggested:
https://github.com/zenovich/runkit/issues/54#issuecomment-22764898

The assumption that once you define a function/constant/class it stays defined.  
That may not sound dangerous, but it is.

Don't get me wrong, I wrote runkit, I don't dislike it from a "use with caution" 
point of view.  You'll have a massive uphill battle getting it (or similar 
manipulation behavior) into the standard distribution bowever.  When you do, what 
will you have?  A couple fewer steps while compiling...

I'm just trying to save you some time with a quick answer.

I see. From what you are saying this is not only ruling out any possibility to include runkit in PHP's core, but also eliminating metaprogramming from ever being employed in this language? If so, Id say its such a tragedy...

Sure class/method/constant stays defined is a huge assumption, breaking it can cause some serious trouble. However, I do believe there are times we have to turn the tides and move forward. Wasnt PHP assumed to be a mere templating language to begin with, wasnt PHP assumed to be a purely procedural language a few years ago, and wasnt PHP's functions/methods assumed to be passing by value instead of reference until PHP 5? 

Anyway I thank you for your patient replies and for making runkit in the very place. Sad it wont be making the core of PHP, but even so Id at least hope something else can be done to enable metaprogramming.

I would like to put in my vote for runkit / metaprogramming integration! I know its unlikely but it would open up a lot of possibilities for dynamic programming. I am writing a CMS / cart system with a MVC structure.  I would like to enable the possibility of extending classes (Controllers) at runtime to enable different plugins to extend the same class to override methods to alter the data passed to template files (Views).

Eg:
I have a class Controller_Product.
I have a plugin class Plugin_Controller_Product extends Controller_Product.
I have a 2nd plugin (built by some other guy) class Plugin2_Controller_Product extends ControllerProduct.

At runtime I would override any calls to Controller_Product with Plugin_Controller_Product. At the same time, with rootkit I could change Plugin2_Controller_Product to extend Plugin_Controller_Product. Therefore I am successfully keeping the functionality for both plugins available at the same time without the plugins ever having to know about each other.

I know I could achieve a simliar effect with composition (and synchronize the data between the 2 classes), but the runkit method would be a cleaner solution in my opinion and I would imagine would have better performance and less complexity.

However, I cannot implement the runkit method because its not packaged with PHP! This CMS / Cart will be installed on shared hosting systems which will not have the option to install runkit. 


Hoping that this real world example would help add some relevancy to the argument! PHP is always evolving, so even ideas about PHP's core functionality should be open for change! Especially since you would have to actually call these runkit / metaprogramming functions to notice any difference in PHP functionality. If you're using meta-programming code it is your responsibility to understand the consequences!

Well it seems highly unlikely though, PHP internals are doing whatever they can to prevent every little chance for possible metaprogramming. Look at this bug ticket and you will understand why:
https://bugs.php.net/bug.php?id=50029

I'd understand if runkits is not possible to integrate with PHP, but the above issue is just plainly annoying. *sigh*