Pass a variable to a parent form in twig - forms

Question

I need to pass a variable to a parent form in twig:
{# This block is called for the children and the parent #}
{% block form_rows %}
{% for child in form %}
{% if child.vars.foo == 'bar' %}
{% set form.vars = form.vars|merge({'key': 'value'}) %}
{% endif %}
{# Parent check children key var #}
{% if child.vars.key %}
{# do something #}
{% endif %}
{# Will call children form_rows block recursively #}
{{ form_row(child) }}
{% endfor %}
{% endblock form_rows %}
This of course don't work because you cannot set a variable like this and form is an object not an array.
I couldn't find any solution until now.

Answer 1

Ok, the whole thing is a bad idea, but it should be possible since Twig v1.2 using the attribute function. For that you need a setter Method in you form object, eg:
class YourFormClass {
public $vars;
/* your class code comes here */
public function setVars($newVars) {
$this->vars = $newVars;
}
}
Assuming that the twig form variable is an instance of YourFormClass you can now use the attribute function like this:
{% set newVal = form.vars|merge({'key': 'value'}) %}
{{ attribute(form, 'setVars', [newVal]) }}
{{ dump(form.vars) }}