How to get Twig support for $$var like syntax?

page.html.twig

{% for i in 0..50 %}
    {% set someanswer = 'answer_' ~ i %}
    {% if form.{{someanswer}} is defined %}
        <div class="question">
            {{ form_label(form.{{someanswer}}) }}
            {{ form_errors(form.{{someanswer}}) }}
            {{ form_widget(form.{{someanswer}}_0, {'attr': {'class':'test_choices'} }) }}
        </div>
    {% endif %}
{% endfor %}