use_tracer=

# File lib/irb/ext/tracer.rb, line 30
    def use_tracer=(opt)
      if opt
        Tracer.set_get_line_procs(@irb_path) {
          |line_no, *rests|
          @io.line(line_no)
        }
      elsif !opt && @use_tracer
        Tracer.off
      end
      @use_tracer=opt
    end