PHP returning static variable by reference

Question

Ignore the namespaces etc could any one explain why I can't return a reference to my static array? Effectively the class is a getter and setter. I wanted to use static methods as the class will never need to be instantiated again throughout the applications life cycle.

I understand what I'm doing might just be "bad practice" - any more knowledge on this matter would be appreciated.

namespace xtend\core\classes; 
use xtend\core\classes\exceptions;

class registry {

private static $global_registry = array();

private function __construct() {}

public static function add($key, $store) {
    if (!isset(self::$global_registry[$key])) {
        self::$global_registry[$key] = $store;
    } else {
        throw new exceptions\invalidParameterException(
            "Failed to add the registry. The key $key already exists."
        );
    }
}

public static function remove($key) {
    if (isset(self::$global_registry[$key])) {
        unset(self::$global_registry[$key]);
    } else {
        throw new exceptions\invalidParameterException(
            "Cannot remove key $key does not exist in the registry"
        );
    }
}

public static function &get($key) {
    if (isset(self::$global_registry[$key])) {
        $ref =& self::$global_registry[$key];
        return $ref;
    } else {
        throw new exceptions\invalidParameterException(
            "Cannot get key $key does not exist in the registry"
        );
    }
}

}

Using it like this

$test = array("my","array");
\xtend\core\classes\registry::add("config",&$test);
$test2 =& \xtend\core\classes\registry::get("config");
$test2[0] = "notmy";    
print_r($test);

Your would presume I would get back

array("notmy","array");

But I just get back the original.

Answer 1

Executive summary:

class Registry {
    private static $global_registry = array();

    public static function Add($key, &$value){
        static::$global_registry[$key] =& $value;
    }
    public static function &Get($key){
        return static::$global_registry[$key];
    }
    public static function Remove($key){
        unset(static::$global_registry[$key]);
    }
}

$test = array("my", "array");
Registry::Add("config", $test);
$test2 =& Registry::Get("config");
$test2[0] = "notmy";    
var_dump($test);

It's really quite simple once you understand how it works:

• Firstly, the add function must pass by reference, otherwise the value that is seen in the function isn't even the value that you have passed in.

• Secondly, when storing the value in $global_registry, we must assign by reference. Otherwise, the value stored isn't even the value seen in the function.

• Thirdly, we must return by reference by putting an ampersand in the function declaration. You have already done this, except this code:

$ref =& self::$global_registry[$key]; // redundant line
return $ref;

Is the same as this code:

return self::$global_registry[$key];

Because in the line public static function &get, we have already declared that the return value is a reference.

• And Lastly, we need to assign the returned reference by reference, which you have also did:

$test2 =& Registry::Get("config");

As you can can see, the whole chain must be by reference. If any one of the step is not done by referece, it wouldn't work.