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

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

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 5

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

Answer 6

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;
?>

Answer 7

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