Re: Listing objects

Dikkie Dik wrote:
> As Peter Fox has pointed out, put the tasks where they belong. I have
> the feeling that you are playing the role of a conductor who has to
> learn each musician how to play as well.
>
> Use clear names for objects. If your model represents companies,
> departments, employees, tasks and subtasks, just call your classes those
> descriptive names.

I figured that much :)

>
> If you have to compare different instances that might have the same
> state (value of internal variables), you could give the class an
> IsEqualTo method to do the comparison. Even better, a lazy collection
> can be used to ensure that equal objects are actually the same instance.
> You could then just use the reference equality operator (===).

Hmm.. $a === $b will return true if $a == $b (i.e. their properties have
the same values) and they are of the same class. That doesn't mean they
are the same object, though..

Ok, let me try a clearer version :)

Object
   |
   +--- App
   | ::$page
   |
   +--- Control
   | ::$parent
   | ::$data
   | ::$object
   |
   +--- Data
   | ::$id
   |
   +--- Template
          | ::owner
          | ::control
          |
          +--- Page

In the main script I have

$app = new App();

In constructors I have

function App() {
    ...
    $null = null;
    $this->page = new Page($null);
}

function Page(&$owner) {
    parent::Template(&$owner);
}

function Template(&$owner) {
    $this->owner = &$owner;
    ...
    $this->control = new Control(&$this);
}

function Control(&$parent) {
    $this->parent = &$parent;
    ...
    $this->data = new Data();
    ...
    if (already_exists($this->data->id)) {
       echo "Duplicate ID";
       return;
    }
    ...
    if ($some_condition) {
       $object = new $CustomSubclassOfTemplate($this->parent);
    }
}

function Data() {
    ...
    $this->id = $some_retrieved_id;
}

Basically, the interesting part is:

When Template is instantiated (initially Page in App constructor), it
instantiates Control, which, in turn, instantiates Data. At this point,
$data->id will be set.
At the end of Control's constructor, if some condition is satisfied, a
subclass of Template will be instantiated and stored in Control's $object.
Thus, we can have:
$app->$page->$control->$object->$control->$object->...->$control->null($object)
We can also pretty much go bottom-up through Template objects via $owner
and we can get the Template object from Control via $parent.

Now, in the middle of Control's constructor there is a check that
$data-id does not already exist.

One way would be to go through Templates:

$temp = $this->parent;
while (isset($temp)) {
   if ($this->data->id == $temp->control->data->id) {
      echo "error";
      return;
   }
}

Apparently this does not work, even though owner is passed by reference.

Another way would be to have a global array and save all objects there
by reference. This is actually more appealing to me, since then I could
access any object at any time from anywhere. Say, if I have an array of
objects under Template and each of them has an associative array
key=>value, then to "compile" an associative array from all those
arrays, I'd simply iterate through the global array, check object's
class, and take in the key/value pairs in the resulting array, rather
than traverse a tree of Templates and those objects. Anyways, what I
tried is something like this:

global $objects;
$objects = array();

class Object() {
    global $objects;
    $objects[count($objects)] = &$this;
}

However, if a property of an object is changed, the object in $objects
stays the same.. But then, it must be a copy?

luph
Received on Tue Jan 3 03:50:22 2006