Passing by reference is not working as expected

Question

Why in the below simplified Plugins system example, passing by reference ($data) is not working ($content is not modified)?

class Plugins
{
    public static function runhook()
    {
       $args = func_get_args();
       $hook = array_shift($args);
       foreach ($args as &$a); // be able to pass $args by reference
       call_user_func_array(array('Plugin', $hook), $args);
    }

}

class Plugin
{
    public static function modifData(&$data)
    {
       $data = 'Modified! :'.$data;
    }
}

class Application
{
    public $content;

    public function __construct()
    {
       $this->content = 'Content from application...';
    }

    public function test()
    {
       echo $this->content; // return 'Content from application...'
       Plugins::runHoook('modifData', $this->content);
       echo $this->content; // return 'Content from application...' instead of 'Modified! :Content from application...'

    }
}

$app = new Application();
$app->test();

As you can see $this->content should be modified by the modifData() called in background by runHook() function of the Plugin class. But for a strange reason nothing expected happens and the variable stay stuck in his original state... Maybe I'm wrong?

Thanks in advance for any help...

IT's because you are only passing by reference to the Plugin class. Plugins::runHook isn't recieving a reference — Pinoniq, Aug 31 '14 at 13:57
FWIT, you can just pass the whole object because objects are always passed by reference. — Ryan, Aug 31 '14 at 16:28
@Pinoniq Thanks for the explanation i will try in the original code — Albertine, Aug 31 '14 at 17:10

score 0 · Accepted Answer · edited May 23 '17 at 10:33

Not possible with a variable amount of paramters (see also https://stackoverflow.com/a/7035513/684353).

You could achieve it with this (repeat this for the amount of parameters you're expecting, which shouldn't be too many):

<?php

class Plugins
{
    public static function runHook($hook, &$param1)
    {
       $args = func_get_args();
    //   call_user_func_array(array('Plugin', $hook), [$param1]); // doesn't work, probably can fix this but didn't seem necessary 
       Plugin::$hook($param1);
    }

}

class Plugin
{
    public static function modifData(&$data)
    {
       $data = 'Modified! :'.$data;
    }
}

class Application
{
    public $content;

    public function __construct()
    {
       $this->content = 'Content from application...';
    }

    public function test()
    {
       echo $this->content; // return 'Content from application...'
       Plugins::runHook('modifData', $this->content);
       echo $this->content; // return 'Content from application...' instead of 'Modified! :Content from application...'

    }
}

$app = new Application();
$app->test();

Or wait for PHP 5.6 and hope the ... token will allow this.

Oh okay, so I could search for a very long time if it's just not possible! Thank you for the explanation, i'll try something based on your example :) — Albertine, Aug 31 '14 at 17:15

Passing by reference is not working as expected

1 Answers1