Symfony FormType getParent vs Inheritance - symfony

Question

When creating a custom field in Symfony, there is a method we define getParent
We define our class by extending from AbstractType class, then return a parent type using getParent method. instead of extending from parent class.
I want to know the philosophy behind this approach.
Is it possible to define my custom type like:
class ImageType extends FileType
{
public function getName()
{
return 'image';
}
}
instead of this :
class ImageType extends AbstractType
{
public function getParent()
{
return 'file';
}
public function getName()
{
return 'image';
}
}
If can, then what is the difference between these two approach?
Thanks!

Answer 1

There are two main differences:
The first one is about FormTypeExtensions. These extensions modify certain form types (e.g: they could change/add some default options, or even add a field).
Using the first approach (e.g. Inheritance), all extensions for the FileType type will be applied to the ImageType, but using the second approach (e.g. getParent), they won't, thus you have more control over your structure.
The second difference is about modifying the behaviour of the parent form inside child form, using buildForm and buildView.
Using the first approach (e.g. Inheritance), will override the base class's methods if you provide them in child, but the second approach (e.g. getParent) will add the child's logic to that of parent.
Consider the following example:
// FileType
public function buildForm(FormBuilderInterface $builder, array $options){
$builder->add('name', 'text');
}
// ImageType
public function buildForm(FormBuilderInterface $builder, array $options){
$builder->add('email', 'email');
}
Inheritance:
form fields: [email]
getParent
form fields: [name] [email]

Answer 2

No, you need to extend using AbstractType. This is used for displaying and building a form and is not a simple entity that you are extending. The base type, FileType in your case, relates to an file with specific methods and you will be allowed to easily override them but extending through AbstractType and can add new fields. If you extended FileType, I do not think Symfony2 would load any new functions properly.
I think the first method is more compact and would like to use it, but I think this would cause problems if you are adjusting the buildView or setDefaultOptions, or adding another method that was not part of the base type.