require 'fiddle' class Object def find_nearest spec found = nil [-1, 1].map { |dir| Thread.new { |i = 0| while !found && i += dir obj = ObjectSpace._id2ref __id__ + i rescue next break found = obj if spec === obj end } }.each(&:join) found end end e = Enumerator.new { |y| y << 42 } e.next p e.find_nearest Fiber