new vs mutation in Ruby

benchmark_new.rb

require "benchmark"

TIMES = 5_000_000

class Node
  attr_accessor :color, :left, :value, :right

  def initialize(color, left, value, right)
    @color = color
    @left = left
    @value = value
    @right = right
  end
end

node = Node.new(:R, nil, 0, nil)

Benchmark.bmbm do |bm|
  bm.report("new") do
    c = 0
    while c < TIMES
      Node.new(:B, nil, 0, nil)
      c += 1
    end
  end
  bm.report("color=") do
    c = 0
    while c < TIMES
      node.color = :B
      c += 1
    end
  end
end

CRuby

% jruby -v --server -X+C benchmark_new.rb
jruby 1.7.0.dev (ruby-1.9.3-p139) (2012-04-24 6a30d22) (Java HotSpot(TM) 64-Bit Server VM 1.7.0_03) [linux-amd64-java]
Rehearsal ------------------------------------------
new      1.290000   0.110000   1.400000 (  0.974000)
color=   0.200000   0.010000   0.210000 (  0.172000)
--------------------------------- total: 1.610000sec

             user     system      total        real
new      0.760000   0.000000   0.760000 (  0.663000)
color=   0.160000   0.000000   0.160000 (  0.133000)

JRuby

% ruby -v benchmark_new.rb 
ruby 2.0.0dev (2012-04-24 trunk 35453) [x86_64-linux]
Rehearsal ------------------------------------------
new      2.780000   0.000000   2.780000 (  2.792829)
color=   0.360000   0.000000   0.360000 (  0.363622)
--------------------------------- total: 3.140000sec

             user     system      total        real
new      2.710000   0.000000   2.710000 (  2.718985)
color=   0.370000   0.000000   0.370000 (  0.372109)