the_dup_cost.rb

require 'benchmark'


class Tester
  attr_accessor :hash

  HASH = Hash[*(1..100).to_a]

  def init_with_dup
    @hash = HASH.dup
  end

  def init_with_hash
    @hash = Hash[HASH]
  end

  def init_with_copy
    @hash = HASH
  end

  def look_all_up
    50.times{|i| @hash[i]}
  end

  def look_all_up_with_fallback
    @bla = nil
    50.times{|i| @bla[i] if @bla; @hash[i]}
  end
end


@iterations = 100_000

@tester = Tester.new

Benchmark.bmbm do |x|
  x.report("init with dup") do
    @iterations.times{@tester.init_with_dup}
  end

  x.report("init with hash") do
    @iterations.times{@tester.init_with_hash}
  end

  x.report("init with copy") do
    @iterations.times{@tester.init_with_copy}
  end

  x.report("init with dup with lookup") do
    @iterations.times{@tester.init_with_dup; @tester.look_all_up}
  end

  x.report("init with hash with lookup") do
    @iterations.times{@tester.init_with_hash; @tester.look_all_up}
  end

  x.report("init with copy with lookup") do
    @iterations.times{@tester.init_with_copy; @tester.look_all_up}
  end

  x.report("init with copy with fallback lookup") do
    @iterations.times{@tester.init_with_copy; @tester.look_all_up_with_fallback}
  end
end

                                          user     system      total        real
init with dup                         0.730000   0.000000   0.730000 (  0.743440)
init with hash                        0.380000   0.000000   0.380000 (  0.386889)
init with copy                        0.000000   0.000000   0.000000 (  0.006719)
init with dup with lookup             1.080000   0.000000   1.080000 (  1.085757)
init with hash with lookup            0.760000   0.000000   0.760000 (  0.768564)
init with copy with lookup            0.400000   0.000000   0.400000 (  0.407021)
init with copy with fallback lookup   0.410000   0.000000   0.410000 (  0.408564)