bm_array.rb

require 'benchmark'

n = (ARGV.shift || 1000000).to_i

def append(words, n)
  n.times { res = words.inject("") {|string, p| string << "#{p}_"} }
end

def join_under(words, n)
  n.times { res = words.map{|s| s}.join("_") }
end

def join(words, n)
  n.times { res = words.map{|s| "#{s}_"}.join }
end

def tainted(words, n)
  n.times { res = words.map {|s| s.tainted? } }
end

def empty_loop(words, n)
  n.times { res = words.map {|s| s} }
end

words = ["string", :symbol, "string", "string", "string"]
Benchmark.bmbm(20) do |x|

  x.report('<< "_"') do
    append words, n
  end

  x.report("join('_')") do
    join_under words, n
  end

  x.report("join()") do
    join words, n
  end

  x.report("tainted?") do
    tainted words, n
  end

  x.report("loop") do
    empty_loop words, n
  end
end

gistfile2.txt

gauss:rubinius brian$ ruby1.8.7 -v bm_array.rb 
ruby 1.8.7 (2010-12-23 patchlevel 330) [i686-darwin9.8.0]
Rehearsal -------------------------------------------------------
<< "_"                8.120000   0.020000   8.140000 (  8.227373)
join('_')             2.870000   0.010000   2.880000 (  2.933932)
join()                4.980000   0.020000   5.000000 (  5.045320)
tainted?              1.830000   0.010000   1.840000 (  1.856563)
loop                  1.480000   0.000000   1.480000 (  1.505634)
--------------------------------------------- total: 19.340000sec

                          user     system      total        real
<< "_"                8.070000   0.020000   8.090000 (  8.171541)
join('_')             2.880000   0.010000   2.890000 (  2.894225)
join()                4.990000   0.010000   5.000000 (  5.063031)
tainted?              1.830000   0.000000   1.830000 (  1.852958)
loop                  1.480000   0.010000   1.490000 (  1.483677)
gauss:rubinius brian$ ruby1.9.2 -v bm_array.rb 
ruby 1.9.2p136 (2010-12-25 revision 30365) [i386-darwin9.8.0]
Rehearsal -------------------------------------------------------
<< "_"                4.510000   0.020000   4.530000 (  4.609053)
join('_')             2.710000   0.010000   2.720000 (  2.745341)
join()                4.000000   0.020000   4.020000 (  4.080192)
tainted?              1.530000   0.010000   1.540000 (  1.551690)
loop                  1.170000   0.000000   1.170000 (  1.177142)
--------------------------------------------- total: 13.980000sec

                          user     system      total        real
<< "_"                4.500000   0.020000   4.520000 (  4.572382)
join('_')             2.710000   0.010000   2.720000 (  2.840988)
join()                4.010000   0.020000   4.030000 (  4.080698)
tainted?              1.530000   0.010000   1.540000 (  1.558215)
loop                  1.170000   0.000000   1.170000 (  1.390231)
gauss:rubinius brian$ rbx -v bm_array.rb 
rubinius 1.2.1dev (1.8.7 52bb1a5b 2010-12-21 JI) [i686-apple-darwin9.8.0]
Rehearsal -------------------------------------------------------
<< "_"                4.719420   0.024558   4.743978 (  4.771132)
join('_')             4.988875   0.027527   5.016402 (  4.931477)
join()                4.760687   0.018208   4.778895 (  4.807103)
tainted?              1.301048   0.005075   1.306123 (  1.304868)
loop                  1.101795   0.004335   1.106130 (  1.097168)
--------------------------------------------- total: 16.951528sec

                          user     system      total        real
<< "_"                4.469994   0.017340   4.487334 (  4.564750)
join('_')             4.368997   0.015696   4.384693 (  4.475056)
join()                4.706614   0.016826   4.723440 (  4.787101)
tainted?              1.339720   0.005845   1.345565 (  1.322900)
loop                  1.073459   0.003020   1.076479 (  1.083705)