Override twig variable in included template in Symfony 3 - symfony

Question

I'm trying to override a variable in the included template.
Can I do this in a Symfony3 & Twig?
My twig template looks like this:
{% set foo = 'bar' %}
{% include 'first.html.twig' %}
{% include 'second.html.twig' %}
// first.html.twig
{{ foo }}
{% set foo = 'second' %}
// second.html.twig
{{ foo }}
I get such a result:
bar bar
But I expect:
bar second

Answer 1

The following Twig code:
{% set a = 42 %}
{{ include("first.twig") }}
Will be compiled to this one:
// line 1
$context["a"] = 42;
// line 2
echo twig_include($this->env, $context, "first.twig");
And twig_include prototype is:
# lib/Twig/Extension/Core.php
function twig_include(Twig_Environment $env, $context, $template, $variables = array(), $withContext = true, $ignoreMissing = false, $sandboxed = false)
So variables are passed by copy, not by reference in included templates. Thus your changes in included templates won't be reflected to including templates.
Moreover, since Twig 2.0, you can't call TwigEnvironment::addGlobal once twig runtime is initialized, so you can't glitch using simple extensions.
All in all, you can understand that if you need to update variables cross templates, it means some template contains business logic and Twig isn't build for that. You need to prepare the whole context in controllers.

Answer 2

Alternatively you may call a PHP class method from TWIG. Example of a page-counter needed when generating a pdf.
Custom class :
class PageCounter
{
private $pageNumber = 0;
public function incrementPageCounter()
{
$this->pageNumber ++;
return $this->pageNumber;
}
}
Controller:
....
$twigVariables = [
...
'pageCounter' => new PageCounter()
];
return $this->render('template.html.twig', $twigVariables);
Twig template (object pageCounter available from any included template)
{{ pageCounter.incrementPageCounter() }} / {{totalPages}}

Answer 3

You just need to do the check and override the variable with another variable :))
{% if name is defined %}
{% set foo = name %}
{% else %}
{% set foo = 'bar' %}
{% endif %}
{% include 'first.html.twig' %}
{% include 'second.html.twig' %}
// first.html.twig
{% set name = 'first' %}
// second.html.twig
{% set name = 'second' %}

Answer 4

Why not override your variable with your include tag/function like :
{% include 'first.html.twig' with {'foo': 'second'} %}
or :
{ include('first.html.twig', {foo: 'second'}) }}