One of the nice features of WordPress is the plugin system, where ‘hooks’ allow custom functionality to be added without monkeying around with the core functionality.
I haven’t played around with this myself yet, but from what I could gather from the documentation, it does this using functions which are all defined in the global scope.
I was wondering today whether similar functionality could be achieved using a more object-oriented approach.
I wanted to be able to extend core functionality of one object by registering ‘hook’ methods on other objects at specific execution points. So I threw together the following code as a demo:
/**
* Binding class - represents a single event binding
*/
class Binding {
var $oObj;
var $sMethod;
/**
* Constructor
* @param object &$oObj the object on which we wish to call a method, passed by referenct
* @param string $sMethod the method to call
*/
function __construct(&$oObj, $sMethod) {
$this->oObj = $oObj;
$this->sMethod = $sMethod;
}
/**
* Trigger the event
* @param $aArgs an array of arguments for the bound function
*/
function trigger($aArgs = array()) {
call_user_func_array(array($this->oObj, $this->sMethod), $aArgs);
}
}
/**
* Singleton class to hold all event bindings
*/
class Hook {
/**
* Stores the static instance of this object - singleton design pattern
* @param object
*/
private static $instance;
/**
* Array of hooks
*/
private $aHooks = array();
/**
* Constructor
*/
private function __construct() {
}
/**
* get instance of this object
*/
public static function getInstance() {
if (!self::$instance)
{
self::$instance = new Hook();
}
return self::$instance;
}
/**
* Bind functionality
* @param string $sEvent the name of the event to bind
* @param object &$oObj the object whose method we wish to call
* @param string $sMethod the method to call
*/
function bind($sEvent, &$oObj, $sMethod) {
$this->aHooks[$sEvent][] = new Binding($oObj, $sMethod);
}
/**
* Trigger a bound event
* @param string $sEvent the event to trigger
* @param array $aArgs an array of arguments to pass to the bound function
*/
function trigger($sEvent, $aArgs = array()) {
if(array_key_exists($sEvent, $this->aHooks)) {
foreach($this->aHooks[$sEvent] as $key => $Binding) {
$Binding->trigger($aArgs);
}
}
}
}
class Extend {
function __construct() {
$Hook = Hook::getInstance();
$Hook->bind('pre', $this, 'beforeDoSomething');
$Hook->bind('post',$this, 'afterDoSomething');
}
function beforeDoSomething($arg) {
echo '<li>This before... the calling function wanted to say"' . $arg . '"';
}
function afterDoSomething($arg) {
echo '<li>The calling function said "' . $arg . '"';
}
}
class Extend2 {
function __construct() {
$Hook = Hook::getInstance();
$Hook->bind('post', $this, 'beforeDoSomething');
}
function beforeDoSomething() {
echo '<li>This is done in a second extended object';
}
}
/**
* Class providing base functionality
*/
class Base {
function __construct() {
}
function doSomething() {
$Hook = Hook::getInstance();
$Hook->trigger('pre', array("I'm about to start doing something..."));
echo '<li>doing the core functionality...';
$Hook->trigger('post', array("Ok I'm all done now!"));
}
}
$Base = new Base();
$Extend = new Extend();
$Extend2 = new Extend2();
$Base->doSomething();
Hopefully someone will find it useful 
& 0xFF;
$b = $rgb & 0xFF;
// Brightness defined 0-1
$brightness = ($r + $g + $b) / (3 * $this->max_rgb);
// Greyness by measuring difference between channels defined 0-1
$rg = 255 - abs($r - $g); // Range 0-255
$rb = 255 - abs($r - $b); // Range 0-255
$gb = 255 - abs($g - $b); // Range 0-255
$greyness = ($rg + $rb + $gb) / (3 * $this->max_rgb);
// Alpha value - combines the brightness and greyness of the image using power laws so they drop off rapidly
$alpha = $this->max_alpha * pow($brightness, 2) * pow($greyness, 3);
// Create new partially transparent colour
$new_colour = imagecolorallocatealpha( $new , $r , $g , $b , $alpha);
// Set pixel with new partially transparent colour in new image
imagesetpixel ($new , $x, $y , $new_colour );
}
}
$this->newim = $new;
}
/**
* Save the new PNG to the specified file
*/
function toFile($file) {
imagepng($this->newim, $file);
}
/**
* Resample
*/
function resample($iNewWidth = 100) {
settype($iNewWidth, 'int');
// Aspect ratio
$r = $this->w_orig / $this->h_orig; // Aspect ratio
// Calculate new height
$iNewHeight = floor($iNewWidth/$r);
$newim = imagecreatetruecolor($iNewWidth, $iNewHeight); // Create new image
// Turn off alpha blending and set alpha flag
imagealphablending($newim, false);
imagesavealpha($newim, true);
$success = ImageCopyResampled($newim, $this->newim, 0, 0, 0, 0, $iNewWidth, $iNewHeight, $this->w_orig, $this->h_orig);
$this->newim = $newim;
}
/**
* Stream to output
*/
function stream() {
header('content-type: image/png');
imagepng($this->newim, null);
}
}
?>