Ruby benchmark: Array#each vs for x in array

each_benchmark.rb

#!/usr/bin/env ruby -w
require "benchmark"

TIMES = 100_000
ARRAY = (1..1_000).to_a

Benchmark.bm(30) do |b|
  b.report "each" do
    TIMES.times do |i|
      ARRAY.each do |element|
      end
    end
  end

  b.report "for ... in" do
    TIMES.times do |i|
      for x in ARRAY
      end
    end
  end
end

__END__
                                    user     system      total        real
each                            9.710000   0.010000   9.720000 (  9.740620)
for ... in                      7.460000   0.000000   7.460000 (  7.475158)

This is more likely a side effect of how the JIT optimizes one block of code and then the other block of code. These two pieces of code compile to the exact same IR and bytecode.

ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-linux]

                                     user     system      total        real
each                             4.910000   0.000000   4.910000 (  4.916322)
for ... in                       6.780000   0.000000   6.780000 (  6.783303)
for ... in 0..limit              8.390000   0.000000   8.390000 (  8.396801)
while i <ARRAY.size              7.920000   0.000000   7.920000 (  7.936485)
while i <limit                   6.100000   0.000000   6.100000 (  6.101939)

Ruby 2.7.0

each                             2.158537   0.000000   2.158537 (  2.159440)
for ... in                       2.278251   0.000000   2.278251 (  2.279027)
for ... in 0..limit              2.698481   0.000000   2.698481 (  2.699452)
while i <ARRAY.size              1.650970   0.000000   1.650970 (  1.651618)
while i <limit                   1.560133   0.000000   1.560133 (  1.560785)

ruby 3.0.2p107 (2021-07-07 revision 0db68f0233) [x86_64-linux]

                                     user     system      total        real
each                             2.767563   0.001415   2.768978 (  2.769054)
for ... in                       2.910278   0.000017   2.910295 (  2.910301)
for ... in 0..limit              3.669667   0.000005   3.669672 (  3.669689)
while i < ARRAY.size             2.346777   0.000007   2.346784 (  2.346790)
while i < limit                  1.973913   0.000000   1.973913 (  1.973939)

ruby 3.1.2p20 (2022-04-12 revision 4491bb740a) [x86_64-linux]

                                     user     system      total        real
each                             6.655506   0.011998   6.667504 (  6.668422)
for ... in                       7.203961   0.008000   7.211961 (  7.212894)
for ... in 0..limit              8.075872   0.012000   8.087872 (  8.088514)
while i <ARRAY.size              4.219771   0.008000   4.227771 (  4.227991)
while i <limit                   3.359660   0.003999   3.363659 (  3.363865)

ruby 3.2.1 (2023-02-08 revision 31819e82c8) [x86_64-linux]

                                     user     system      total        real
each                             2.052966   0.000207   2.053173 (  2.053209)
for ... in                       2.225467   0.000006   2.225473 (  2.225489)
for ... in 0..limit              2.478339   0.000000   2.478339 (  2.478365)
while i <ARRAY.size              1.727570   0.000000   1.727570 (  1.727601)
while i <limit                   1.469423   0.000001   1.469424 (  1.469439)

ruby 3.2.2 (2023-03-30 revision e51014f9c0) [x64-mingw-ucrt]

                                   user     system      total        real
each                             4.203000   0.000000   4.203000 (  4.222868)
for ... in                       4.562000   0.000000   4.562000 (  4.583148)
for ... in 0..limit              5.047000   0.000000   5.047000 (  5.050032)
while i <ARRAY.size              2.219000   0.000000   2.219000 (  2.235048)
while i <limit                   1.984000   0.000000   1.984000 (  2.017428)

ruby 3.3.1 (2024-04-23 revision c56cd86388) [x86_64-linux]

                                     user     system      total        real
each                             3.574591   0.000000   3.574591 (  3.586114)
for ... in                       3.879859   0.000000   3.879859 (  3.892989)
for ... in 0..limit              4.631031   0.000000   4.631031 (  4.637611)
while i <ARRAY.size              2.519849   0.000000   2.519849 (  2.520258)
while i <limit                   1.927129   0.000000   1.927129 (  1.927600)