each_with_index.rb

require 'benchmark'

arr = (1..100).to_a


Benchmark.bm(20) do |x|
  x.report("each.with_index") do
    100_000.times do
      arr.each_with_index do |v, i|
      end
    end
  end

  x.report("each.with_index b&") do
    100_000.times do
      bv = arr.each.with_index
      arr.length.times do |i|
        bv.next
      end
    end
  end

end

                           user     system      total        real
each.with_index        0.590000   0.000000   0.590000 (  0.591757)
each.with_index b&    11.630000   0.040000  11.670000 ( 11.685133)

                       user     system      total        real

each.with_index 0.780000 0.000000 0.780000 ( 0.787362)
each.with_index b& 7.700000 1.980000 9.680000 ( 9.699257)

Seems a Fiber adds about 1 ms per call. Wonder what this would look like if you compared Fibers against Threads.