    # File lib/spec/matchers/extensions/instance_exec.rb, line 7
        def instance_exec(*args, &block)
          begin
            orig_critical, Thread.critical = Thread.critical, true
            n = 0
            n += 1 while respond_to?(method_name="__instance_exec#{n}")
            InstanceExecHelper.module_eval{ define_method(method_name, &block) }
          ensure
            Thread.critical = orig_critical
          end
          begin
            return send(method_name, *args)
          ensure
            InstanceExecHelper.module_eval{ remove_method(method_name) } rescue nil
          end
        end