gistfile1

require 'benchmark'
require 'benchmark/ips'

class Test
  attr_reader :instance_var

  def initialize
    @instance_var = 'value'
  end
end

object = Test.new

Benchmark.ips do |x|
  x.report { object.instance_var }
  x.report { object.instance_variable_get :@instance_var }
end

# $ ruby -v
# ruby 1.9.3p194 (2012-04-20 revision 35410) [x86_64-darwin12.0.0]
# $ ruby ivar_benchmark.rb
# Calculating -------------------------------------
#                          42823 i/100ms
#                          51152 i/100ms
# -------------------------------------------------
#                       2603014.6 (±3.9%) i/s -   13018192 in   5.011281s
#                       2372758.6 (±2.4%) i/s -   11867264 in   5.005498s