etag_mapping.rb

require 'digest/md5'
require 'benchmark'

parts = []
body  = ['Hello World']

Benchmark.bm do |x|
  x.report('each') do
    body.each { |part| parts << part }
    Digest::MD5.hexdigest(parts.join)
  end
  x.report('map') do
    parts = body.map  { |part| part }
    Digest::MD5.hexdigest(parts.join)
  end
end

#          user        system      total        real
# each    0.000000   0.000000     0.000000  (  0.000078)
# map     0.000000   0.000000     0.000000  (  0.000012)