Can PHP do Singleton Classes??

[ppowell]

Consider this:

class ActionHandler {

/*-------------------------------------------------------------------------------------------------------------------------------------------------------------------
	This class will be a singleton class structure by calling its constructor by reference only (prefixed by '&').  Is primarly used to
	reference its errorArray Array property as a single reference to allow for static usage
--------------------------------------------------------------------------------------------------------------------------------------------------------------------*/

var $isSuccessful = true;					// BOOLEAN PROPERTY DETERMINING IF ACTION WAS SUCCESSFUL
var $tableName;							// DB TABLE NAME PROPERTY
var $fileName;							// FILE NAME PROPERTY
var $dbConn;							// DB CONNECTION OBJECT
var $dbConnObj;							// DB RESOURCE LINK OBJECT


/*---------------------------------------------------------------------------------------------------------------------------------------------------------
	Remember that you since this class will be extended by other classes especially in action.inc.php, for properties to
	have value into the class this extends into, you will have to not "construct" them here since this constructor will not
	be called directly by the extended class.
------------------------------------------------------------------------------------------------------------------------------------------------------------*/
function &ActionHandler() {							//  SINGLETON CONSTRUCTOR
	static $errorArray = array();						// ASSOCIATIVE ARRAY PROPERTY FIELD => ERROR MSG
}

//----------------------------------------------------* GETTER/SETTER METHODS *--------------------------------------------------------------

function &getErrorArray() {												// STATIC ARRAY METHOD
	return $this->errorArray;
}


function &getHTMLRedirect($myImmedAction, $additionalQS = '') {			// STATIC HTML/JAVASCRIPT STRING METHOD
	global $section, $clientFolderName, $projectFolderName, $redirectArray;
	if ($redirectArray[$section][$myImmedAction] && $myImmedAction) {
	 $html = "\n<script>\n <!--\n location.href = '/$clientFolderName/$projectFolderName/index.php?section=$section&action=" .
	                $redirectArray[$section][$myImmedAction] . '&success=' . urlencode($this->getSuccessMsg());
	 $html .= ($additionalQS) ? '&amp;' . urlencode($additionalQS) : '';
	 $html .= "';\n //-->\n</script>\n<noscript>\n<meta http-equiv=\"Refresh\" content=\"1;URL=/$clientFolderName/$projectFolderNameindex.php?" .
	                 "section=$section&action=" . $redirectArray[$section][$myImmedAction] . '&success=' . urlencode($this->getSuccessMsg());
	 $html .= ($additionalQS) ? '&amp;' . urlencode($additionalQS) : '';
	 $html .= "\">\n</noscript>\n\n";
	}
	return $html;
}

function &getSuccessMsg() {												// STATIC STRING METHOD
	global $action, $choice, $db;
	return 'Successful ' . strtoupper($action) . ' ' . strtoupper($choice) . " to database $db - <a href=index.php?willViewLog=1>View Log</a><p>";
}

function setErrorArray($additionalErrorArray) {								// VOID METHOD
	if (is_array($this->errorArray) && @sizeof($this->errorArray) > 0 && is_array($additionalErrorArray) && @sizeof($additionalErrorArray) > 0) {
	 $this->errorArray =& $this->errorArray + $additionalErrorArray;
	} elseif (is_array($additionalErrorArray) && @sizeof($additionalErrorArray) > 0) {
	 $this->errorArray =& $additionalErrorArray;
	}
}

//--------------------------------------------------* END OF GETTER/SETTER METHODS *-------------------------------------------------------------------------

function &convert_to_HTML($content) {								// STATIC HTML STRING METHOD
	$content = preg_replace('/[\n\r]/i', '<BR>', $content);
	$content = preg_replace('/[\s]/i', '&nbsp;', $content);
	return $content;
}

function &convert_to_text($content) {									// STATIC TEXT STRING METHOD
	$content = preg_replace('/<br[^>]*>/i', '\n', $content);
	$content = preg_replace('/&nbsp;/i', '\s', $content);
	return $content;
}

}

THAT is my entire supposed Singleton class in its actual entirety. It is set up that way to call static methods upon a static array. That way, whenever you have this call in your class:

if (somethingsWrong) ActionHandler::setErrorArray('action' => 'Something is wrong'));

However, consider this example: I call an instance of a FileGenerator class from my ActionPerformer->perform() method. FileGenerator class object's getBackupFile() method does some code and if it breaks:

ActionHandler::setErrorArray('action' => 'Something is wrong'));

Everything in the FileGenerator class object method works just fine and were I to do this:

print_r(ActionHandler::getErrorArray());

I see:

Array (action => Something is wrong)

But the moment I leave the getBackupFile() method from FileGenerator class object and return to the code in ActionPerformer->perform() method and were I do this:

print_r(ActionHandler::getErrorArray());

I see:

Array ()

How then in PHP do you assure that anytime I call ActionHandler::setErrorArray() that the error array, which is supposed to be static, remains a single-instance entity with a value available to ALL classes everywhere? How do you build a singleton class in PHP?

Phil

[ahundiak]

The basic problem is that for:
ActionHandler::getErrorArray()
the getErrorArray method is not allowed to use $this. Which makes sense because $this is the current object but no object actually exists.

I know you are trying to avoid using globals but for php4 you can make your life easier by doing something like:

function getErrorArray()
{
  if (!isset($GLOBALS['master_error_array'])) {
    $GLOBALS['master_error_array']) = array();
  }
  return $GLOBALS['master_error_array'];
}

Once PHP5 is released then you can go back and tweak the class to use static variables.

A singleton class is a different concept. With a singleton you create one and only one instance of an object. Typically, you would add a singleton method to the class and use a global to store the single object.

function &singleton()
{
  if (!isset($GLOBALS['master_action_handler'])) {
    $GLOBALS['master_error_object'] = new ActionHandler();
  }
  return $GLOBALS['master_error_object'];
}

// To check for the error log */
$masterHandler =& ActionHandler::singleton();
print_r($masterHandler->getErrorArray());

Withe a singleton, the static class variables issue goes away.

[ppowell]

That is truly non-Java OO.. wow.. but thanx, and incidentally it's $GLOBALS not $_GLOBALS that worked for me.

Phil

[ppowell]

Ok someone please explain this one to me, I'm lost completely:

class ActionHandler {

  function &ActionHandler() {
   static $errorArray = array();
  }

  function &getErrorArray() {
   return $GLOBALS[$errorArray];
  }

  function &setErrorArray($additionalErrorArray) {
   if (is_array($additionalErrorArray)) 
    array_merge($this->errorArray, $additionalErrorArray);
   if (!isset($GLOBALS[$errorArray])) $GLOBALS[$errorArray] = $this->errorArray;
  }

}

Would someone please explain why I have to use:

$GLOBALS[$errorArray]

and the array is populated

but if I use

$GLOBALS['errorArray']

the very same array is null?

Phil

[goldbug]

In the first example, you are using a variable to reference an array key. In the second, you use an unchanging string.
For example:

$cow = array();

$foo = 'bar';

$cow['foo'] = 'moo';
$cow[$foo] = 'oink';

// Will display "moo"
echo $cow['foo'];

// Will display "oink";
echo $cow[$foo];

// Will ALSO display "oink"
echo $cow['bar'];

Simply put, the parser evaluates the value of $foo, then uses the result as the key name for the array.

[ppowell]

Sorry, your example does not seem to make sense in light of my problem.

if (!isset($GLOBALS['errorArray'])) $GLOBALS['errorArray'] = $this->errorArray;

The value of $GLOBALS['errorArray'] is NULL

if (!isset($GLOBALS[$errorArray])) $GLOBALS[$errorArray] = $this->errorArray;

The value of $GLOBALS[$errorArray] is whatever $this->errorArray is.

Why does this happen? $errorArray is never set at all!

Phil

[goldbug]

Ahh, I misunderstood. However, as to your current issue...I've no clue off the top of my head.

[ppowell]

One of the Zend gurus in NYC (love that town!) came up with a wild kludge to my problem:

class ActionHandler {

  function &ActionHandler() {
   static $errorArray = array();
  }

  function &getErrorArray() {
   return ActionHandler::setErrorArray();
  }

  function &setErrorArray($additionalErrorArray) {
   static $errorArray = array();
   if (is_array($additionalErrorArray)) $errorArray += $additionalErrorArray;
   return $errorArray;
  }

}

I absolutely don't understand it but it works!

Phil