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Date: Thu, 11 Nov 2004 20:17:33 +0100
Reply-To: Marcus Boerger <helly@php.net>
Message-ID: <535857716.20041111201733@marcus-boerger.de>
To: Jason Perkins <jperkins@sneer.org>
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Subject: Re: [PHP-DEV] __get() "feature"
From: helly@php.net (Marcus Boerger)

Hello Jason,

Thursday, November 11, 2004, 4:21:23 PM, you wrote:

> I've ran into an issue using __get() and want to ascertain if this is 
> how it was intended to work or if it's a bug. The general notion of 
> what I'm attempting to accomplish using __get() is that a given object 
> will potentially contain other objects, but these contained objects 
> aren't known (or generated) until runtime.

> For example, we'll instantiate a sales_order object and then, using its 
> has_a() method, add a customer object to it. To prevent cascades of 
> objects being instantiated, I'd plan to use lazy initialization - the 
> customer object won't be instantiated until the first time that it's 
> accessed through the customer class. The problem that I'm having is 
> that lazy initialization in PHP 5 is accomplished via the __get() 
> method which is called when an attribute (or contained class in this) 
> isn't available - it's passed the name of the property that wasn't 
> found and that's not enough information for me to return the attribute 
> of the contained object that was being accessed. Here's some quickly 
> written code with extra code stripped that'll demonstrate what I mean:

> <?

> class sales_order {
>      ...

>    public function has_a( $class ) {
>      $this->relationships[ $class ] = 'has_a';
>    }

>    public function __get( $class ) {
>      if(array_key_exists( $class, $this->relationships )) {
>        if( $this->relationships[ $class ] == 'has_a') {
>          $this->$class  = new $class( $this->id );
>          return;
Change the above line to:
          return $this->$class;

>        }
>      }
>    }
> }

> So if $attribute exists in the relationships array, it's instantiated 
> (and, yeah, I plan to move the contained objects into a declared array. 
> one thing at a time :) )

> $sales_order = new sales_order;
> $sales_order->has_a( customer );
> print $sales_order->customer->name;

> The last line fails, because __get is passed only 'customer' and not 
> 'customer->name' - I have no way of knowing what attribute of customer 
> was being accessed, so I can't return the requested data. Running this 
> code:

> $sales_order = new sales_order;
> $sales_order->has_a( customer );
> print $sales_order->customer->name;
> print $sales_order->customer->name;

> the fourth line works, because the customer object was instantiated 
> during line three (line three still fails to return a value). Is this 
> an issue with __get() or is this how it was intended to work?


> --
> Jason N Perkins




-- 
Best regards,
 Marcus                            mailto:helly@php.net