[RESOLVED] Classes with lists/collections

[Rodders]

Hi folks

I'm still getting to grips with OOP in PHP, though I work with VB.Net everyday. As such I'm trying to create a little web-based administration system for my 5-a-side football team.

I have a Squad class which needs to contain a list of all the players in the squad.

With VB.Net I would simply define my class like this:

<?php

class Squad
{
	//Properties
	public $Name;
	public $Season;
	public $Division;
	public $ListOfPlayers;
}

?>

Where ListOfPlayers is a collection that allows me to add players (instances of the Player class) and remove players.

So, is there a similar "collection" thing within PHP?

Or, will I need to write my own "collection"? If I do that, I'd like it to be generic so I can have a "collection of Player" or a "collection of Match" or a "collection of EmailAddress" etc.

Thanks in advance

[laserlight]

You would likely use an array, which in PHP can function as a numerically indexed array, or an associative array (i.e., a map or dictionary).

[Rodders]

OK, and thanks for the quick reply.

My understanding is that arrays are of fixed dimension. So, to add to it you effectively have to create a new one and copy the contents across. Of course, there is built-in functions to do this but is it good for performance?

array_pop and array_push I assume are the functions to use.

How would I begin to implement this in my class?

I want $ListOfPlayers to be an array, but can I tell it that only instances of the Player class can be added? Perhaps I need to set my property as Private and then do some further code within my Squad class to check the type of object that is being added to ListOfPlayers and deal with it accordingly?

I believe I can use Type Hinting in my constructor?

	class Squad
	{
		//Properties
		public $Name;
		public $Season;
		public $Division;
		public $ListOfPlayers;
	}

	//Contructor
	function __construct($name, $season, $division, array $players) {
	}
}

[laserlight]

Rodders wrote:

My understanding is that arrays are of fixed dimension. So, to add to it you effectively have to create a new one and copy the contents across.

That is not true. You might want to read the PHP manual on arrays.

Rodders wrote:

I want $ListOfPlayers to be an array, but can I tell it that only instances of the Player class can be added? Perhaps I need to set my property as Private and then do some further code within my Squad class to check the type of object that is being added to ListOfPlayers and deal with it accordingly?

I believe I can use Type Hinting in my constructor?

Yes, type hinting should be what you want. However, constraining the type to be an array type still means that an array of objects of an unexpected type can be provided, unfortunately. On the other hand, you can provide a method that accepts a Player object as an argument, and which then adds this Player to the member array.

[Rodders]

Thanks.
I think my misunderstanding about arrays comes from using VB.Net, in which they are fixed dimension....I vaguely recall having a similar discussion on here a few months ago about that same issue.

OK, I think I can work out how to use type hinting to control adding and removing players from my array. I'll go and have a play around to see what I can come up with.

Thanks.

[Rodders]

Resolved.
I found an article explaining how to extend the ArrayObject base class to include type checking. So, I now force my $ListOfPlayers property to be of type PlayerList. PlayerList is an extended ArrayObject which checks the type of anything you try to append to it.

squad.php

<?php

class Squad
{
	//Properties
	public $Name;
	public $Season;
	public $Division;
	public $Players;

	//Contructor
	function __construct($name, $season, $division, PlayerList $players) {
		$this->Name = trim($name);
		$this->Season = trim($season);
		$this->Division = trim($division);
		$this->Players = $players;
	}
}

?>

playerlist.php

<?php

require_once("classes/typesafearray.php");
require_once("classes/player.php");

// An attempt at creating a strongly typed array implementation
class PlayerList extends TypeSafeArray
{
	protected function typeCheck($val)
	{
		if (!is_a($val, "Player"))
		{
			throw new Exception("Only objects of type 'Player' can be added to PlayerList.");
		}

		return true;

	}
}

?>

typesafearray.php

<?php

// The inspiration and code for this came from:
// http://liamgraham.wordpress.com/2007/05/21/typesafe-arrays-for-php/

abstract class TypeSafeArray extends ArrayObject
{
	// Override ArrayObject::append
	public function append($val)
	{
		$this->typeCheck($val);
		parent::append($val);
	}

	// Override ArrayObject::offsetSet
	// used when setting values with []
	public function offsetSet($index, $val)
	{
		$this->typeCheck($val);
		parent::offsetSet($index, $val);
	}

	// Abstract function typeCheck, to be implemented
	// by subclasses to define type-checking behaviour
	abstract protected function typeCheck($val);

}

?>