OOP architecture advice

[bunner_bob]

I'm building a fairly complex site, and I've been teaching myself the use of classes recently and am starting to implement them.

At present, my typical page structure is a set of includes to build the html page, build the nav bar, build the body portion of the page, build the sidebar, and add a footer. Within two of the sections (body and sidebar) I use classes to assemble whatever is going to be there.

I'm thinking it might be cooler/better to just do a single class for the page, and populate the component sections using functions within that class, rather than having a non-oop structure defining the page and only using classes within it.

On the other hand, I like the fact that the sidebar is its own self-contained class, as is the main content area. It seems more elegant than having a single giant class with a whole lot of functions inside it. My class file is currrently well over 3000 lines already, though I do plan to split it up into "admin" and "public" portions, both inheriting from a common parent. I'll probably do these as separate files.

What'd make me really happy is a class for the page, and then a separate class for each section within the page - but I can't nest classes/objects this way can I? If I did, how would any "$this->" references know which "$this->" to point to?

Basically, I can't decide which way to go and am looking for some advice.

Thanks
- Bob

[swr]

Be sure to understand the difference between a class, and an object (an instance of a class).

Objects can contain references to other objects. Like so (untested):

class Page {
    var $parts;

function addPart(&$part) {
    $this->parts[] =& $part;
}

function renderAllParts() {
    for ($i = 0; $i < count($this->parts); $i++) {
        $this->parts[$i]->render();
    }
}
}

$page =& new Page();

$page->addPart(new Header());
$page->addPart(new LeftNav());
$page->addPart(new Content());
$page->addPart(new RightNav());
$page->addPart(new Footer());

$page->renderAllParts();

[bunner_bob]

Ahh - there is hope.

I'm not familiar with the "=&" operator - can you suggest a link to learn more about it?

Also, is there a way to call methods within the "sub classes"? So that if I'm not using constructors, or need to activate certain methods I can get at them? I'd think using $this=>method would only access methods in the "master" class.

• Bob

[Weedpacket]

Originally posted by bunner bob
I'm not familiar with the "=&" operator - can you suggest a link to learn more about it?

It's two operators; the assignment operator = and the reference operator &.

[bunner_bob]

OK - this is hurting my brain a bit...

I'm not sure why I'd want to use $a =& $b instead of just $a = $b. I Realize that with &=, any changes I make to one will be made to the other (which I guess is the point, right?). But why would I need two variables with different names and the same content? Kind of like having two identical cars.

In the case of creating objects, there seems to be a fondness for using
$bar =& new fooclass();
The manual says if you just use "=" you're making a copy of the object. But isn't any instance a copy of an object? Or does the act of typing "new fooclass()" actually create the object, in which case $bar = new fooclass() actually makes two objects: "$bar", and something called "new fooclass()" that you can't really access?

Thanks for your patience...

• Bob

[swr]

For OOP it's important to not copy. Each copy is a different object.

Suppose you have code like this:

function addPartToPage($page, $part) {
    $page->addPart($part);
}

$myPage = new Page();
addPartToPage($myPage, new Header());

That won't do anything. More precicely, it'll create a copy of $myPage, add the part to it, then discard the copy. The original $myPage will not have any header added to it. You need to use a reference, like so:

function addPartToPage(&$page, &$part) {

The & causes the function arguments to be passed by reference.

For OOP it is normal to assign objects by reference. In PHP5, objects will be assigned by reference, by default. Most other object-oriented languages work that way.

Always use & when working with objects, unless you are absolutely certain that you want to copy your object.

Also, be aware that with PHP 4 some language constructs always copy. foreach, for example. So if you have code like this:

foreach ($this->parts as $part) {
    $part->html .= "<p>Blah!</p>";
}

it won't do anything to $html in the original $this->parts, because $part is a copy. That's why I used a traditional for loop in my example. It wouldn't have made a difference in my example (assuming render() doesn't change the state of the object), but it is a good practice to not copy your objects needlessly.

[freebie]

You might consider checking out the smarty templating engine. It probably has all the functionality you need.
http://smarty.php.net
http://smarty.php.net/manual/en/

[bunner_bob]

Hmmm - yeah, that's a lot like what I'm after - and will probably end up with after a few years of continual tweaking & improvement. I'm building an engine that I'll end up reusing on a number of sites, continually evolving as I learn more and discover more things I want to do.

I'll have to study what the smarty folks are doing...

• Bob

[bunner_bob]

Sorry to be thick (still) - but - swr - when you wrote:

$this->parts[$i]->render();

in your example above, were you implying there was a method in each of those parts called "render()", and by the quoted line of code, you were activating the method inside the "part" (which is itself inside the "page" object)?

• Bob

[swr]

Yes, each object in the $parts array in $page would have it's render() method invoked.