b.rb

# http://patshaughnessy.net/2012/1/4/never-create-ruby-strings-longer-than-23-characters

require 'benchmark'

ITERATIONS = 2000000 # original script was 1000000

def run(str, bench, op=nil)
  p = case op
  when :<<
    lambda { new_string = str << "x" } # String#<< は破壊的なので毎回strも変わる
  else
    lambda { new_string = str + "x" }
  end
  bench.report("#{str.length + 1} chars by #{op}") do
    ITERATIONS.times do
      p.call
    end
  end
end

Benchmark.bm do |bench|
  [:<<, :+].each do |op|
    run("12345678901234567890", bench, op)
    run("123456789012345678901", bench, op)
    run("1234567890123456789012", bench, op)
    run("12345678901234567890123", bench, op)
    run("123456789012345678901234", bench, op)
    run("1234567890123456789012345", bench, op)
    run("12345678901234567890123456", bench, op)
  end
end

=begin
$ ruby -v
ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-linux]


      user     system      total        real
21 chars by <<  0.570000   0.000000   0.570000 (  0.569075)
22 chars by <<  0.560000   0.000000   0.560000 (  0.560594)
23 chars by <<  0.570000   0.000000   0.570000 (  0.562083)
24 chars by <<  0.580000   0.000000   0.580000 (  0.583945)
25 chars by <<  0.590000   0.000000   0.590000 (  0.591878)
26 chars by <<  0.560000   0.000000   0.560000 (  0.563446)
27 chars by <<  0.560000   0.000000   0.560000 (  0.558477)
21 chars by +  0.630000   0.000000   0.630000 (  0.627031)
22 chars by +  0.700000   0.000000   0.700000 (  0.703161)
23 chars by +  0.700000   0.000000   0.700000 (  0.694024)
24 chars by +  0.780000   0.000000   0.780000 (  0.789131)
25 chars by +  0.790000   0.000000   0.790000 (  0.789473)
26 chars by +  0.790000   0.000000   0.790000 (  0.796314)
27 chars by +  0.800000   0.000000   0.800000 (  0.797088)
=end