retrieve_variable

# File actionpack/lib/action_view/renderer/partial_renderer.rb, line 409
    def retrieve_variable(path)
      variable = @options.fetch(:as) { path[%_?(\w+)(\.\w+)*$', 1] }.try(:to_sym)
      variable_counter = :"#{variable}_counter" if @collection
      [variable, variable_counter]
    end