yeti

<?php

/*

I have a question here regarding object orientation in PHP and any other
language.

Let's start with some hypothetical code:

*/

// <--- 1st CLASS

class ParkingLot {

var size; // size in sq feet

var max_number_of_cars; // how many cars there is space for

function __construct($size, $max_cars) {

$this->size = $size; $this->max_number_of_cars = $max_cars;

}

};

cpark = new ParkingLot(50000, 17);

// <--- 2nd CLASS

class ParkingSpace extends ParkingLot {

var ps_ID; // ID of the parking space ( 1 .. max_number_of_cars )

var occupied_by; // ID of the car on the parking space

var st_time; // Unix time stamp set when the car parks

function __construct($car, $id) {

$this->st_time = time();

$this->occupied_by = $car;

$this->ps_ID = $id;

}

};

/*

OK, so i got a parking lot class and its subclass parking space.

Now the question:

I want a list of occupied parking spaces, where do I put that? One might put
it into the ParkingLot Class, but wouldn't that be a recursion (a child
instance in the parent class)?

*/

$occ_parking_spaces = array();

$occ_parking_spaces[] =& new ParkingSpace('Joes Car', 8);

$occ_parking_spaces[] =& new ParkingSpace('My Prshe', 17);

$occ_parking_spaces[] =& new ParkingSpace('Toms Caddy', 4);

/*

After a while a method to print all occupied spaces is necessary. Correct me
if I'm wrong, but I usually add it to the ParkingLot class.

class ParkingLot {

// previous code ...

var $occ_parking_spaces = array();

function print_occ_spaces() {

var_dump($this->occ_parking_spaces)

}

};

What bothers me here is that I'm actually having a list of child classes in
the parent class, is there a better/correct way to do this?

I hope I made myself clear.

Greetz,

Yeti

*/

?>

robert

Here's the point of your comfusion. ParkingSpace is not really a
ParkingLot is it? I mean you could say a parking lot having a single
parking space qualifies, but not really. I see you problem being similar
to apples versus apple tree. You wouldn't do the following (would you?):

<?php

class AppleTree
{
}

class Apple extends AppleTree { }
?>

Cheers,
Rob.
--
http://www.interjinn.com
Application and Templating Framework for PHP

ted-talks

Object-oriented programming, with it's "class" and "object" approach,
is meant to model real life more closely than functional programming.

In, a "parking space" is physically inside a "parking lot", but a
parking space is not a subclass of a parking lot. It's not a variation
or mini parking lot. It's an entirely different entity. A parking lot
consists of parking spaces, but a parking space is its own thing.

In other words, don't extend ParkingSpace from ParkingLot. They should
be separate classes entirely.

As for the recursion... no, that won't be a problem. Each ParkingSpace
you're instantiating is a separate instance, and won't be related to
the parent ParkingLot in anyway way internally.

<?php

class ParkingSpace {
var $size;
var $num_spaces;
var $spaces = array();
}

class ParkingSpace {
var $ps_ID;
var $occupied_by;
var $st_time;
}

?>

In the above class definition, simply populate the $spaces array with
instances of the ParkingSpace class.

~Ted

ted-talks

Corrected code example:

(too early in the morning to think)

<?php

class ParkingLot {
var $size;
var $num_spaces;
var $spaces = array();
}

class ParkingSpace {
var $ps_ID;
var $occupied_by;
var $st_time;
}

?>

In the above class definition, simply populate the $spaces array with
instances of the ParkingSpace class.

~Ted

eric.butera

Listen to what everyone else has said so far. Look up IS-A versus
HAS-A. Favor composition over inheritance. You want your parking lot
to have spaces, but spaces don't have to be in a parking lot.

http://www.javacamp.org/moreclasses/oop/oop5.html

eric.butera

---------- Forwarded message ----------
From: Yeti <yeti@myhich.com>
Date: Fri, Jul 11, 2008 at 2:08 PM
Subject: Re: [php] Question regarding OO
To: Eric Butera <eric.butera@gmail.com>


I understand my error in thinking now.

Apple can't extend Tree.

Oak, Evergreen or Willow extend Tree.

I thank you all for helping me to understand.

jblanchard

[snip]
I understand my error in thinking now.

Apple can't extend Tree.

Oak, Evergreen or Willow extend Tree.

I thank you all for helping me to understand.
[/snip]

By jove, I think he's got it!

Parking space could be a member variable of parking lot, that would make
sense.

tmboyd1

One thing at a time, Jay... one thing at a time.


Todd Boyd
Web Programmer