It's RUBY time :) - Strongly typed arraylists in Ruby

Hey Guys,

I was trying out Ruby and in the program below I am attempting to create a strongly typed ArrayList :) Seriously, I really really enjoy programming in Ruby :) Let me know if you have any comments...!

# Author - Karthik Ananthapadmanaban
# Date/Time  - 11/21/2009 1.43 AM
# Updated on - 11/21/2009 11.21 AM

# A simple module that encrypts/decypts strings
# Similar to caesar's cipher
module Crypt
class Cryptor
  def Encrypt(string)
    @str1 = ""
    string.each_byte{|x| @str1 = @str1 + ((x+1).chr)}
    return @str1
  end

  def Decrypt(string)
    @str1 = ""
    string.each_byte{|x| @str1 = @str1 + ((x-1).chr)}
    return @str1
  end
end
end

# A simple module that implements
# various arithmetic operations
module Math
  class Arithmetic
      def Add(num1,num2)
          return num1+num2
      end

      def Sub(num1,num2)
          return num1-num2
      end

      def Mul(num1,num2)
          return num1*num2
      end

      def Div(num1,num2)
          return num1/num2
      end

      def Sqr(num1)
          return num1*num1
      end

      def Sqrt(num1)
          return num1 ** 0.5
      end
end
end

# As we all know, ruby is dynamically typed
# I just wanted to create a class 
# that allows only manipulating a certain type
# so,  the result is a strongly typed class (trivially?) :)
# Yes, in C# ArrayList items are not strongly typed, 
# against List<>, where the items are strongly typed <>
# comments are welcome ;)
module Collections
  class ArrayList
      def initialize (defType)
          @defaultType = defType
          @objArr = []
          
          @posIndex = 0
      end
    
      def Add(someObj)
        if (someObj.class.to_s.eql?(@defaultType))
          puts("Adding the object")
          @objArr.push(someObj)
        else
          puts("Not adding the object")
        end
      end
      
      def Get
        return @objArr
      end

      # Why don't you just use Array.At? :)
      def GetItemAt(pos)
        for obj in @objArr
            
            if (@posIndex == pos.to_i)
                @posIndex = 0
                return obj
            else
                @posIndex = @posIndex +1  
            end            
        end
      end
  end
end

include Crypt
include Math
include Collections

cr = Cryptor.new
puts(cr.Encrypt("this is a very very very long string"))
puts(cr.Decrypt(cr.Encrypt("this is a very very very long string")))

puts("\n")

m1 = Arithmetic.new
m2 = Arithmetic.new
m3 = Arithmetic.new
m4 = Arithmetic.new
m5 = Arithmetic.new

# coll = ArrayList.new("Math::Arithmetic")
# or
coll = ArrayList.new(m1.class.to_s)

# All of the following would be added
coll.Add(m1)
coll.Add(m2)
coll.Add(m3)
coll.Add(m4)
coll.Add(m5)

puts("\n")

# This wouldn't be added
coll.Add(cr)

puts("\n")

i = 10

for obj in coll.Get
  puts(obj.Add(4,i))
  i = i+1
end

puts("\n")

puts("Number of items: ")
puts(coll.Get.length)

puts("\n")

# This would work
obj = coll.GetItemAt(3)
puts(obj.Add(4,10))

puts("\n")

# This wouldn't work
# As the obj would be undefined, an error would be 
# generated at the top
obj = coll.GetItemAt(30)
puts(obj.Add(4,10))

Thanks and Happy coding :)