Here's something I came up with that works with PHP5 or higher because it uses "magic methods" (__get, __set, __call, etc.) and is_callable and call_user_func_array. Basically it lets you take any class and convert it into a plugin class that you can override class methods and properties with new values, or use it to log existing values (such as to a log or notification system), as well as block a class property or class method from executing with the given argument(s).
I list it for your comments. I like this better than the Observer Pattern (see the stackoverflow.com reference above) because it doesn't require that you extend your class, and it doesn't require you add any special things inside your class. The only thing that might be a pain is that call_user_func_array tends to run a little slow (as in another few microseconds) according to some discussion on the web about this, and then I make it another more microseconds slower by having it run my plugin code. However, if you want the plugin architecture, I guess you have to accept this -- where even the Observer Pattern introduces some more microseconds of time.
Code: Select all
<?php
////////////////////
// PART 1
////////////////////
class Plugin {
private $_RefObject;
private $_Class = '';
public function __construct(&$RefObject) {
$this->_Class = get_class(&$RefObject);
$this->_RefObject = $RefObject;
}
public function __set($sProperty,$mixed) {
$sPlugin = $this->_Class . '_' . $sProperty . '_setEvent';
if (is_callable($sPlugin)) {
$mixed = call_user_func_array($sPlugin, $mixed);
}
$this->_RefObject->$sProperty = $mixed;
}
public function __get($sProperty) {
$asItems = (array) $this->_RefObject;
$mixed = $asItems[$sProperty];
$sPlugin = $this->_Class . '_' . $sProperty . '_getEvent';
if (is_callable($sPlugin)) {
$mixed = call_user_func_array($sPlugin, $mixed);
}
return $mixed;
}
public function __call($sMethod,$mixed) {
$sPlugin = $this->_Class . '_' . $sMethod . '_beforeEvent';
if (is_callable($sPlugin)) {
$mixed = call_user_func_array($sPlugin, $mixed);
}
if ($mixed != 'BLOCK_EVENT') {
call_user_func_array(array(&$this->_RefObject, $sMethod), $mixed);
$sPlugin = $this->_Class . '_' . $sMethod . '_afterEvent';
if (is_callable($sPlugin)) {
call_user_func_array($sPlugin, $mixed);
}
}
}
} //end class Plugin
class Pluggable extends Plugin {
} //end class Pluggable
////////////////////
// PART 2
////////////////////
class Dog {
public $Name = '';
public function bark(&$sHow) {
echo "$sHow<br />\n";
}
public function sayName() {
echo "<br />\nMy Name is: " . $this->Name . "<br />\n";
}
} //end class Dog
$Dog = new Dog();
////////////////////
// PART 3
////////////////////
$PDog = new Pluggable($Dog);
function Dog_bark_beforeEvent(&$mixed) {
$mixed = 'Woof'; // Override saying 'meow' with 'Woof'
// $mixed = 'BLOCK_EVENT'; // if you want to block the event
return $mixed;
}
function Dog_bark_afterEvent(&$mixed) {
echo $mixed; // show the override
}
function Dog_Name_setEvent(&$mixed) {
$mixed = 'Coco'; // override 'Fido' with 'Coco'
return $mixed;
}
function Dog_Name_getEvent(&$mixed) {
$mixed = 'Different'; // override 'Coco' with 'Different'
return $mixed;
}
////////////////////
// PART 4
////////////////////
$PDog->Name = 'Fido';
$PDog->Bark('meow');
$PDog->SayName();
echo 'My New Name is: ' . $PDog->Name;
In Part 1, that's what you might include with a require_once() call at the top of your PHP script. It loads the classes to make something pluggable.
In Part 2, that's where we load a class. Note I didn't have to do anything special to the class, which is significantly different than the Observer pattern.
In Part 3, that's where we switch our class around into being "pluggable" (that is, supports plugins that let us override class methods and properties). So, for instance, if you have a web app, you might have a plugin registry, and you could activate plugins here. Notice also the "Dog_bark_beforeEvent" function. If I set $mixed = 'BLOCK_EVENT' before the return statement, it will block the dog from barking and would also block the Dog_bark_afterEvent because there wouldn't be any event.
In Part 4, that's the normal operation code, but notice that what you might think would run does not run like that at all. For instance, the dog does not announce it's name as 'Fido', but 'Coco'. The dog does not say 'meow', but 'Woof'. And when you want to look at the dog's name afterwards, you find it is 'Different' instead of 'Coco'. All those overrides were provided in Part 3.
So how does this work? Well, let's rule out eval() (which everyone says is "evil") and rule out that it's not an Observer pattern. So, the way it works is the sneaky empty class called Pluggable, which does not contain the methods and properties used by the Dog class. Thus, since that occurs, the magic methods will engage for us. That's why in parts 3 and 4 we mess with the object derived from the Pluggable class, not the Dog class itself. Instead, we let the Plugin class do the "touching" on the Dog object for us. (If that's some kind of design pattern I don't know about -- please let me know.)
So, anyway, let me know if you think something could be done better here.