PHP not quite object-oriented?

Anon

Hi!

I designed a small two-object architecture for my needs. It basically consists of the main data-handling class (class DataHandler) and the data-rendering class (DataRenderer). Specific extended classes of DataHandler know how to work with data (extract it from database or array, for instance), and pass this information to the DataRenderer, and when the 'row' of data is done with by the DataRenderer, they receive it, append to results string and go to the next iteration.
First, I designed this architecture with the main render(&$printer) method which iterated through the data and rendered it using the printer. Inside this method, I had something like this:

$result .= $printer->render();

and the $printer had to receive the $data array inside its render() method this way:
$this->handler->data.

However, although I clearly initialized the printer with the handler in the printer's init() method, the above line returned false on each iteration, although print_r($this->handler) produced the expected results.

Now I call the renderer like this:
$printer->render($data) and this works well enough (it is also more correct in terms of reuse, although I am not quite sure which method would be more memory-efficient).

However, the printer may need to know some other information of the handler (such as current row). Sending all these to the printer using $printer->render(...) is crazy.

My question is - what is wrong with PHP (I use 4.0.5)? I also saw some kind of mention about PHP's OOP flaws in Pear's source code. How can I handle my problem?

Thanks a lot in advance.

Best regards,
Stas

Anon

Try {$this->handler}->data ?

[deleted]

A codesample would help.

Anon

Hi and thanks for your answer.

Here's the example. I just discovered that the FALSE result that was returned by the DataPrinter object was specific to that example.
I think the problem is that somehow what we pass by reference to $printer->initHandler() is actually passed by value, so only the data variables specific to that state of the object become known to the $printer object.

Hence, in the script below, 'Microsoft' is printed three times in a row.
I debugged getNext, it does everything correctly.

Here's the script. I would appreciate any help I could get. I tried calling initHandler(&$this) (the documentation says that I only need to specify reference-passing in the function's declarations), so I don't know what else may be wrong.

Thanks in advance.

class DataHandler {
var $raw_data;
var $current_data;
var $currRecord;

function DataHandler($data_arr)
{
	$this->raw_data = $data_arr;
}

function getNext()
{
	if ($d = next($this->raw_data)) {
		return $d;
	} else return false;
}

function getCurrent()
{
	if ($d = current($this->raw_data)) {
		return $d;
	} else return false;
}

function getResults(&$printer)
{
	$results = false;
	reset ($this->raw_data);

	if ($this->current_data = $this->getCurrent()) { // records were returned

		$printer->initHandler($this);

		// cycle through records
		$this->currRecord = 0;

		while(is_array($this->current_data)) {
			$this->currRecord++;
			$results .= $printer->getResults();

			$this->current_data = $this->getNext();
		}

	}

	return $results;
}

}

class DataPrinter {
var $datahandler;

function initHandler(&$handler)
{
	$this->datahandler = $handler;
}

function getResults()
{
	return "<b>" . $this->datahandler->current_data[0] . "</b> <i>". $this->datahandler->current_data[1] . "</i> --- " . $this->datahandler->current_data[2]."<br>\n";
}

}

function Test()
{
$d = new DataHandler(array(array(1, "Microsoft", "Redmond, VA"), array(2, "Borland", ""), array(3, "Oracle", "")));
$p = new DataPrinter;

print $d->getResults($p);

}

Test();

Anon

GRAAAAAAAAAAAAAAAAAAAAAAA
YOUR NOT IN GOOD

Anon

Hi!

Thanks for the reply! For some reason or another (although I know the {} should work in tough cases), I get an error when I try this.

In any case, as I already posted under another message in this thread (with code sample), the problem is probably in PHP somewhere. Maybe it's just not that OOP as it is cracked up to be. :-)

Anyway, I would appreciate any help with this problem.

Thanks a lot in advance!

Stas

Anon

Hi!

I think I found the answer, but I just don't have any idea why! Not according to the php docs, anyway.

I changed the initHandler() method of DataPrinter.

function initHandler(&$handler)
{
$this->datahandler = &$handler;
}

As you can see, I pass an object by pointer, and then initialize the datahandler member variable to a pointer, again!

According to documentation, specifying the reference indicator (&) is enough to pass a reference.

I don't know, sometimes C++ pointers seem more logical than this.

Thanks for all the help!
Best regards,
Stas

[deleted]

no brain?

[deleted]

I'm a bit lost on all of this, you have two classes, and you use methods of the second class in the first, without extending the first on the second. What are your plans? :-)

Anon

Hi!

Well, I share your confusion :-)

Actually, I obviously couldn't upload a working example because it's bigger than this. When working on a few projects, I realized I essentially wasted time on coding data handling routines. Like: Get row from database, add to results, get next row.
When I had to redo an array-based approach (I used to have a dynamic menu which first needed to be small, so I hard-coded an array into the source, but then it had to grow, so I had to use a database), I decided to rethink the whole approach and standardize it a little.
If I extend the first on the second, I lose this functionality:
1) Just as I exemplified above, if I use an array of type array(array(), array()) at first and then go to a database, I will have to make all the printer objects extend another datahandler object, which is a bit stupid since I may still need to handle the raw information interchangeably with either the array-based datahandler or the database-based (perhaps using the phpLib database class or Pear's db class - all of the return a row as an associative array, which is exactly what I need). Then, what also happens is that I also need to change the getCurrent and getNext methods of all (!!!) printers that switched from array to database.
Not very nice, really.

There's a bunch of other things which are whirling around in my head but which I can't think of right now, but having a datahandler and a datarender classes is one of the top five in books on OOP software architectures.

Having a separate printer is also good because I may switch to another data-handling algorithm which will be generic and won't need to create a separate printer for each case.
For instance, we pay pass a row template to the printer (i.e. <tr><td>{firstname} {lastname}</td></tr&gt😉. The printer will replace each macro in the template with the value of the respective key in its data array. This will allow us to make it a very generic and reusable class. But then, if for some reason you will need to switch back to just inserting values into raw HTML, it won't be as difficult as with the standard approached (I mean just plain PHP functions).

The printer could, for example, incapsulate a keycol variable that allows us to print only the unique rows within a non-unique result set. This is also very effective.

I know I am losing a couple of microseconds on processing this way, but I see this as a better way to design software in PHP.

Thanks a lot, I would appreciate your further comments!

Best,
Stas

Anon

Hi!
There's a good example from real life - if I were an employer having a factory with one type of employee who knew how to both handle the data and produce nice readable output from it, I would be a bit surly if I had to employ another one just because none of the employees had time or knowledge to handle a new task.
If I had two types of employees, I would just combine their efforts for the new case.

In the software world, a good example would be printers and report programs - in any case, they never know how the raw data looks or how it should be circulated - they just know how to render it.

PHP may not yet be that fast when handling objects, but it's good enough in many cases and I guess with built-in libraries like Pear in the future, people will eventually accept more reusable architectures over straight php functions.

Thanks for your input, Vincent!

Best regards,
Stas