Is it possible to dynamically add code to/extend a class?

Question

I want to write a sort of "plugin/module" system for my code, and it would make it much easier if I could "add" stuff into a class after it's been defined.

For example, something like this:

class foo {
  public function a() {
     return 'b';
  }
}

There's the class. Now I want to add another function/variable/const to it, after it's defined.

I realize that this is probably not possible, but I need confirmation.

Answer 1

No, you cannot add methods to an already defined class at runtime.

But you can create similar functionality using __call/__callStatic magic methods.

Class Extendable  {
    private $handlers = array();
    public function registerHandler($handler) {
        $this->handlers[] = $handler;
    }

    public function __call($method, $arguments) {
        foreach ($this->handlers as $handler) {
            if (method_exists($handler, $method)) {
                return call_user_func_array(
                    array($handler, $method),
                    $arguments
                );
            }
        }
    }
}

Class myclass extends Extendable {
    public function foo() {
        echo 'foo';
    }
}

CLass myclass2 {
    public function bar() {
        echo 'bar';
    }
}

$myclass = new myclass();
$myclass->registerHandler(new myclass2());

$myclass->foo(); // prints 'foo'
echo "\n";

$myclass->bar(); // prints 'bar'
echo "\n";

This solution is quite limited but maybe it will work for you

Answer 2

To add/change how classes behave at runtime, you should use Decorators and/or Strategies. This is the prefered OO approach over resorting to any magic approaches or monkey patching.

A Decorator wraps an instance of a class and provides the same API as that instance. Any calls are delegated to the wrapped instance and results are modified where needed.

class Decorator 
{
    // …

    public function __construct($decoratedInstance)
    {
        $this->_decoratedInstace = $decoratedInstance;    
    }
    public function someMethod()
    {
        // call original method
        $result = $this->_decoratedInstance->someMethod();
        // decorate and return
        return $result * 10;
    }
    // …
}

For Strategy, see my more complete example at Can I include code into a PHP class?

More details and example code can be found at

• http://sourcemaking.com/design_patterns/decorator
• http://sourcemaking.com/design_patterns/strategy

Answer 3

I have a few methods for you to try. :) Have fun coding.

Method for only one class:

class main_class {
    private $_MODS = array(),...;
    public ...;
    public function __construct(...) {
        ...
        global $MODS_ENABLED;
        $this -> $_MODS = $MODS_ENABLED;
    }
    ...
    public function __get( $var ) {
        foreach ( $this->_MODS as $mod ) 
            if ( property_exists( $mod, $var ) )
                return $mod -> $var;
    }
    public function __call( $method, $args ) {
        foreach ( $this->_MODS as $mod )
            if ( method_exists( $mod, $method ) )
                return call_user_method_array( $method, $mod, $args );
    }
}

Method for when you want to deal with more than one class:

class modMe {
    private $_MODS = array();
    public function __construct__() {
        global $MODS_ENABLED;
        $this -> $_MODS = $MODS_ENABLED;
    }
    public function __get( $var ) {
        foreach ( $this->_MODS as $mod ) 
            if ( property_exists( $mod, $var ) )
                return $mod -> $var;
    }
    public function __call( $method, $args ) {
        foreach ( $this->_MODS as $mod )
            if ( method_exists( $mod, $method ) )
                return call_user_method_array( $method, $mod, $args );
    }
}
class mainClass extends modMe {
    function __construct(...){
        $this -> __construct__();
    }
}

Now lets try to use them:

$MODS_ENABLED = array();
$MODS_ENABLED[] = new mod_mail();
$myObj = new main_class(...);
$myObj -> mail("me@me.me","you@you.you","subject","message/body","Extra:Headers;More:Headers");
# Hey look, my mail class was just added into my main_class for later use.

Note:

I am currently using the first method (I only have one class, the mods are exceptions) in my own CMS that I have made from scratch (http://sitegen.com.au), and it works great, my reason on needing this is because I have my main_class that is getting generated after I have required all mods in ./mods-enabled/* creating functions and changing how other functions work, I will also come back here another time with a solution for two mods to both change a function without one winning as it ran first. I have split my plugins in two, mods that run on every site, and plugins that have settings for a site and may not even be enabled.
Have fun programming.

Answer 4

If it is not enough magic for you, you can use dynamic objects. The common idea is here: https://github.com/ptrofimov/jslikeobject

Answer 5

You can extend the class

class foo {
  public function a() {
     return 'b';
  }
}

class woo extends foo {
  public function newStuff() {
     $var = $this->a();
     echo $var;
  }
}

By extending foo from the woo class the functionality in foo is usable while you can also create new methods in woo. That's the easiest way to add new functionality to a class.

Answer 6

You can use magic functionality of PHP to provide actions on methods that are not defined at compile time.

Answer 7

It is actually possible. For instance:

<?php
class Test {

  function set($set, $val) {
    $this->$set = $val;
  }

  function get($get) {
    return $this->$get;
  } 
}

$t = new Test();
$t->set('hello', 'world');
echo $t->get('hello');
exit; 
?>