# File lib/gettext_i18n_rails/ruby_gettext_extractor.rb, line 42
    def extract_string(node)
      case node.first
      when :str
        node.last
      when :call
        type, recv, meth, args = node
        # node has to be in form of "string" + "other_string"
        return nil unless recv && meth == :+

        first_part  = extract_string(recv)
        second_part = extract_string(args)

        first_part && second_part ? first_part.to_s + second_part.to_s : nil
      else
        nil
      end
    end