part5.rb

# (a)
class Class
  def attr_accessor_with_history attr

    attr = attr.to_s

    attr_reader attr

    class_eval %Q{
      # Create a history method for the attribute
      def #{attr}_history
        # This isn't super elegant, but the homework examples show
        # the arrays starting with nil. See part3.rb for an explanation
        # of ||=
        @#{attr}_arr ||= [nil]
      end

      # Sets the new value and also adds it to the array
      # of values for that attribute
      def #{attr}= newValue
        @#{attr} = newValue
        @#{attr}_arr ||= [nil]
        @#{attr}_arr << newValue
      end
    }
  end

end


class MyClass
  attr_accessor_with_history :foo
  attr_accessor_with_history :bar
end

#foo = MyClass.new
#foo.foo = "hello"
#foo.foo = "world"
#foo.foo = ["another", "thing"]
#puts foo.foo.inspect
#puts foo.foo_history.inspect

#foo = MyClass.new
#foo.bar = "that"
#foo.bar = "that"
#foo.bar = ["this", "thing"]
#puts foo.bar.inspect
#puts foo.bar_history.inspect


class Numeric
  @@currencies = {'yen' => 0.013, 'euro' => 1.292, 'rupee' => 0.019, 'dollar' => 1.0}
  def method_missing(method_id)
    singular_currency = method_id.to_s.gsub( /s$/, '')
    if @@currencies.has_key?(singular_currency)
      self * @@currencies[singular_currency]
    else
      super 
    end
  end 

  def in curr
    curr = curr.to_s

    singular_currency = curr.to_s.gsub( /s$/, '')
    self / @@currencies[curr] if @@currencies.has_key?(curr)
  end
end

# NOTE: I don't think I'm doing this quite right, because 1.rupee.in(:rupees) should just
# return 0.019, but it returns 0.019*0.019. So my solution doesn't really work I don't think.
#puts 1.rupees.in(:rupees)

# (b)


class String
  def palindrome?
    str = self.downcase
    str.gsub! /[\W]/, ""
    str == str.reverse
  end
end

#puts "hello".palindrome?
#puts "lol".palindrome?

# (c)

module Enumerable
  def palindrome?
    # reverse another method that's part of Enumerable, so we let it
    # do all the work
    arr = self.to_a
    arr == arr.reverse
  end
end

puts [1, 0].palindrome?
puts [1, 1].palindrome?
puts [1,2,3,2,1].palindrome?
puts ({ :this => "foo" }.palindrome?)