PHP create new instance of child class based on existing instance of parent class

Question

I know this is going to be a bit of a weird one, so I'll try to be as brief and as clear as possible.

I am working on a plugin for Grav. I have determined that the most effective way to accomplish my goal is to extend one of the base classes, Pages.

The structure looks something like this:

index.php creates an instance of grav class.
Base grav class creates an instance of Pages class and stores it as a service.
After grav class has finished it's loading process, index.php tells grav to run process on it's service handlers.
PagesProcessor runs the init() function on the stored Pages class.
PagesProcessor fires an event signaling that pages have been initalized.
Plugin receives event.

What this looks like in practical terms.

index.php

$grav = Grav::instance(
    array(
        'loader' => $loader
    )
);

Grav.php

protected static $diMap = [
    .....
    'pages' => 'Grav\Common\Page\Pages',
    'pagesProcessor' => 'Grav\Common\Processors\PagesProcessor',
    .....
];

protected $processors = [
    .....
    'pagesProcessor',
    .....
];

public static function instance(array $values = [])
{
    if (!self::$instance) {
        self::$instance = static::load($values);
    .....
    return self::$instance;
}

protected static function load(array $values)
{
    $container = new static($values);
    .....
    $container->registerServices($container);

    return $container;
}

protected function registerServices()
{
    foreach (self::$diMap as $serviceKey => $serviceClass) {
        .....
        $this->registerService($serviceKey, $serviceClass);
        .....
    }
}

protected function registerService($serviceKey, $serviceClass)
{
    $this[$serviceKey] = function ($c) use ($serviceClass) {
        return new $serviceClass($c);
    };
}

index.php
```
try {
    $grav->process();
} 
```

Grav.php

public function process()
{
    foreach ($this->processors as $processor) {
        $processor = $this[$processor];
        .....
            $processor->process();
        .....
    }
    .....
}

PageProcessor.php

public function __construct(Grav $container)
{
    $this->container = $container;
}
public function process()
{
    .....
    $this->container['pages']->init();
    $this->container->fireEvent('onPagesInitialized', new Event(['pages' => $this->container['pages']]));
    .....
}

Finally, Plugin.php

public static function getSubscribedEvents()
{
    return [
        'onPagesInitialized' => ['onPagesInitialized', 0]
    ];
}

public function onPagesInitialized(Event $event) {
    // Do things here...
}

Whew... ok.

Now what I would like to do is extend Pages.php (not listed above) so that I can modify some of it's protected properties that don't have setters nativly. The problem is, there is no way to tell grav to use the extended method until AFTER it's been initailized.

I could always create a new instance of my extended class, initailize it, and overwrite the existing instance, but that means effectivly forcing the initailization twice, which means doubling the processing time, and that's super inefficent.

What I would like to do is something like the following:

Pages.php <- I can't change this:

class Pages
{
    protected $grav;

    protected $instances;

    protected $children;

    protected $routes = [];

    public function __construct(Grav $c)
    {
        $this->grav = $c;
    }
    .....
    public function init()
    {
        .....
        $this->instances = [];
        $this->children = [];
        $this->routes = [];

        $this->buildPages();
    }
    .....

PagesExtended.php <- My class

class PagesExtended extends Pages
{
    public function __construct(Pages $original)
    {
        // set the properties of this class to the original instance
        parent = $original;
    }

    public function setInstances(Array $newInstances){
        $this->instances = $newInstances;
    }
    .....
}

Then in my Plugin.php

public function onPagesInitialized(Event $event) {
    // Do things here...
    $this->grav['pages'] = new PagesExtended($event['pages']);
}

The only other thing I can think of is some sort of __call trick.

So.... Thoughts?

EDIT------------------------

Well... I still would like to know if this can be done, but as it turns out grav "freezes" these services so they can't be overridden..... not very happy right now.

I think it'd be helpful to hear why you're trying to do this. My first thought is that this is a possible XY problem, but regardless, more information about the "why" would help any sort of answer. — Jacobm001, Jun 13 '18 at 15:48

score 0 · Answer 1 · answered Jun 21 '18 at 16:33

0

I don't know what you really want to achieve, but your custom methods for Page must return something and they are used in Twig.

I often put the custom data of Page into page's header. In my plugin, it gets the custom data ($oldHeader = $page->header()), calculate stuff and add the final result to Page object again as a custom new properties ($page->header($newHeader)), then in Twig I can access and print out these new data of my page ({{ page.header.data_generated_in_plugin }}).

This way I can do anything without overriding Page class.

answered Jun 21 '18 at 16:33

Hung Tran

790
2
8
24

Yes, I know how the page headers work. The information from the pages that I wanted to modify are not exposed to plugins at all. Plus, the point was that I needed to avoid overriding the twig files in admin. I was making an admin plugin, but was unable to override a twig file because it would have interfered with a different admin plugin. – Dalen Catt Jun 22 '18 at 23:53

score 0 · Accepted Answer · answered Jun 22 '18 at 23:50

0

It turns out what I was trying to do was impossible in the grav environment, no matter what classes I tried to extend. It could never be done from a plugin because those classes were "frozen" by grav.

answered Jun 22 '18 at 23:50

Dalen Catt

111
1
9

PHP create new instance of child class based on existing instance of parent class

2 Answers2