Variable Empty until Reassigned - php

Question

I am not quite sure why this is happening, or how to properly explain it, but maybe someone can shed some light on this.
I have a CMS system I based off of the CodeIgniter/Opencart Framework utilizing a Registry, Controller and Module. I have run into a scenario where I have previously saved a variable to the registry as:
$this->application_page = 'current/page';
But for some reason when I call it in the application:
echo empty($this->application_page)?'yes':'no';
//Returns Yes
But.. When I Reassign it:
echo empty($this->application_page)?'yes':'no';
//Returns Yes
$page = $this->application_page;
echo empty($page)?'yes':'no';
//Returns No
A var_dump returns:
var_dump($this->application_page);
string 'current/page' (length=12)
I can get around this quite easily by just using $page but I'm curious to know why this is happening?
UPDATE:
So I messed around with the _isset function but didn't get it to work, possibly my error, possibly not.. Here is how it all works together:
class Registry {
private $data = array();
public function get($key){ return (isset($this->data[$key]) ? $this->data[$key] : NULL); }
public function set($key,$val){ $this->data[$key] = $val;
}
abstract class Controller {
protected $registry;
public function __construct($registry){ $this->registry = $registry; }
public function __get($key){ return $this->registry->get($key); }
public function __set($key,$value){ $this->registry->set($key, $value); }
}
class Applications {
private $registry;
function __construct($Registry){ $this->registry = $Registry; }
function __get($key){ return $this->registry->get($key); }
function __set($key,$val){ return $this->registry->set($key,$val); }
public function buildApplication(){
$this->application_page = 'current/page';
$application = new application($this->registry);
}
}
class Application extends Controller {
public function index(){
echo empty($this->application_page)?'yes':'no';
//Returns Yes
$page = $this->application_page;
echo empty($page)?'yes':'no';
//Returns No
}
}
Hopefully this helps?
Had a Typo, Registry's functions are not magic methods. Also $registry was declared in Applications.

Answer 1

The class probably didn't implement the magic __isset() method which is triggered by calling isset() or empty() on inaccessible properties.
Example:
Live demo I:
<?php
class Test {
private $a = '42';
public function __get($name) {
return $this->a;
}
}
$obj = new Test();
var_dump($obj->a); // string(2) "42"
var_dump(empty($obj->a)); // bool(true)
Implementing the __isset() method as follows (Live demo II) will yield the correct result:
public function __isset($name) {
if ($name == 'a') {
return true;
}
return false;
}
// ...
var_dump($obj->a); // string(2) "42"
var_dump(empty($obj->a)); // bool(false)
Here is a new version of your code implementing the __isset() methods: http://ideone.com/rJekJV
Change log:
Added __isset() method to Controller class which internally calls Registry::has().
Added has() method to Registy class.
[Only for testing: Object initialization and running Application::index() method.]
There was one issue (after updating your answer):
You haven't declared $registry as a member variable in the Applications class.
The code fails otherwise because it doesn't access the actual member variable (magic __set() method!)
Also, you had quite some redundancy in your code (not DRY). I hope this isn't production code ;)