new vs mutation in Ruby

benchmark_new.rb

require "benchmark"

TIMES = 1_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
    TIMES.times do |i|
      Node.new(:B, nil, 0, nil)
    end
  end
  bm.report("color=") do
    TIMES.times do |i|
      node.color = :B
    end
  end
end

CRuby

$ ruby-trunk -v benchmark_new.rb
ruby 2.0.0dev (2012-04-18 trunk 35385) [i686-linux]
Rehearsal ------------------------------------------
new      1.030000   0.000000   1.030000 (  1.035411)
color=   0.180000   0.000000   0.180000 (  0.180050)
--------------------------------- total: 1.210000sec

             user     system      total        real
new      1.010000   0.010000   1.020000 (  1.008668)
color=   0.180000   0.000000   0.180000 (  0.181044)

JRuby

$ jruby --1.9 -v benchmark_new.rb
jruby 1.6.7 (ruby-1.9.2-p312) (2012-02-22 3e82bc8) (OpenJDK Server VM 1.6.0_23) [linux-i386-java]
Rehearsal ------------------------------------------
new      0.790000   0.000000   0.790000 (  0.790000)
color=   0.241000   0.000000   0.241000 (  0.241000)
--------------------------------- total: 1.031000sec

             user     system      total        real
new      0.333000   0.000000   0.333000 (  0.333000)
color=   0.154000   0.000000   0.154000 (  0.154000)