Why does Twig require the __invoke method while using custom view helper?
When I want to use my custom view helpers in the Twig template while implementing in the ZF2 based project, I need to add the magic method __invoke method in the view helper; otherwise, Twig template engine throw an error which says about unable to call the __invoke method of the view helper.
Now I want to know why I need to declare this __invoke magic function in the view helpers?
Check the docs: https://framework.zend.com/manual/2.1/en/modules/zend.view.helpers.advanced-usage.html
If you want your helper to be capable of being invoked as if it were a method call of the PhpRenderer, you should also implement an __invoke() method within your helper.
The same must apply with the twig renderer, it's trying to execute the helper class (using invoke as a shortcut)
You can see where the PHPRenderer is using __invoke() as a proxy / shortcut to the helpers:
https://github.com/zendframework/zend-view/blob/master/src/Renderer/PhpRenderer.php#L389
/**
* Overloading: proxy to helpers
*
* Proxies to the attached plugin manager to retrieve, return, and potentially
* execute helpers.
*
* * If the helper does not define __invoke, it will be returned
* * If the helper does define __invoke, it will be called as a functor
*
* @param string $method
* @param array $argv
* @return mixed
*/
public function __call($method, $argv)
{
$plugin = $this->plugin($method);
if (is_callable($plugin)) {
return call_user_func_array($plugin, $argv);
}
return $plugin;
}
I imagine the Twig renderer is just doing something similar, infact we can see below it is:
https://github.com/ZF-Commons/ZfcTwig/blob/master/src/ZfcTwig/View/TwigRenderer.php#L83