Demonstration of the code execution difference in speed when class, object and local variables are used.

cl_obj_loc_perf.rb

# Demonstration of the code execution difference in speed when class, object and local variables are used.
# This example shows class variables performing much much worst, perhaps due to internal synchronization within Ruby engine.
# I've recently noticed that issue, profiling my code, so I don't really know the reason.
# The PI calculation algorithm has been taken somewhere and might be not best, but that's not the point.
# Results:
# MRI 1.9.3
#                   user     system      total        real
# @@class =>  434.228000   0.063000 434.291000 (437.134613)
# @object =>  200.243000   0.031000 200.274000 (202.477156)
# local =>    132.492000   0.000000 132.492000 (133.706739)
#
# JRuby 1.6.5
#                   user     system      total        real
# @@class => 183.354000   0.000000 183.354000 (183.174000)
# @object =>  65.529000   0.000000  65.529000 ( 65.529000)
# local =>    20.658000   0.000000  20.658000 ( 20.658000)

require 'benchmark'

class PiClass
  class << self
    def calculate
      @@num = 4.0
      @@pi = 0
      @@plus = true

      @@den = 1
      while @@den < 10000000
        if @@plus
          @@pi = @@pi + @@num/@@den
          @@plus = false
        else
          @@pi = @@pi - @@num/@@den
          @@plus = true
        end

        @@den += 2
      end

      @@pi
    end
  end
end


class PiObject
  def calculate
    @num = 4.0
    @pi = 0
    @plus = true

    @den = 1
    while @den < 10000000
      if @plus
        @pi = @pi + @num/@den
        @plus = false
      else
        @pi = @pi - @num/@den
        @plus = true
      end

      @den += 2
    end

    @pi
  end
end


class PiLocal
  def calculate
    num = 4.0
    pi = 0
    plus = true

    den = 1
    while den < 10000000
      if plus
        pi = pi + num/den
        plus = false
      else
        pi = pi - num/den
        plus = true
      end

      den += 2
    end

    pi
  end
end


N = 100
Benchmark.bm do |x|
  print '@@class => '
  x.report { N.times { PiClass.calculate } }

  print '@object => '
  pi_obj = PiObject.new
  x.report { N.times { pi_obj.calculate } }

  print 'local => '
  pi_loc = PiLocal.new
  x.report { N.times { pi_loc.calculate } }
end