I just can't extend the Symfony2 Form class. Tried everything - php

Question

I have literally tried everything to try and extend the Symfony2 Form class.
I want to add a new method to Form and call it in a controller:
$form = $this->createForm($this->get('my_form_service'), $entity);
$form->myNewMethod();
Because the Form class isn't defined as a service and is instantiated in another class (FormBuilder, line 221) then I can't see what I can do. I don't want to hack the core.
I could extend the controller class, e.g. the createForm() method returns the instantiated Form object:
// Extend Controller and do something with Form before returning
public function createForm($type, $data = null, array $options = array())
{
return $this->container->get('form.factory')->create($type, $data, $options);
In fact How to add a new method to a php object on the fly? shows how I could do the above and add my new method that way, but my understanding is that you need to at least add __call to the Form class - which I can't do - or the added method won't be able to use $this (which I need).
I only need to add this for when the form is used in a controller. I don't need it for any CLI processing.
Any ideas how I can add a method to the Form class without hacking the core?
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EDIT: Why am I doing this?
I want to 'silently fail' a form submit if a certain criteria is met. I believe the best way to do this would be to do this in a controller:
if ($form->isValid()) {
if ($form->requiresSilentFail()) {
// Silently fail
} else {
// As normal, add to DB etc.
}
}
I suppose I could just do something like this:
if ($form->isValid()) {
if ($this->get('check_my_form')->requiresSilentFail($form)) {
// Silently fail
} else {
// As normal, add to DB etc.
}
}
.... but I need to also perform a little bit of extra logic in Form::handleRequest() first, so I believe extending Form is the only option.

Answer 1

I don't really understand why you need to extend the form class simply on your controller/service where you process the form call your method under is valid check, see below:
$form->handleRequest($request);
if ($form->isValid()) {
$this->get($apiResource->getResourceHandlerName())->update($resourceData);
$response = new Response();
$response->setStatusCode($statusCode);
if ($this->isSuccessFullStatusCode($statusCode)) {
$serializedObject = $this->getSerializer()->serialize($resourceData, 'json',$serializationContext);
$response->setStatusCode($responseStatusCode);
$response->setContent($serializedObject);
return $response;
}
}