Chapter 3 (Ruby)

Saas solutions-to-homework

#Project 4 (this one is credited to https://gist.github.com/tomtung/1973534)
class Class
  def attr_accessor_with_history(attr_name)
    attr_name = attr_name.to_s
    attr_reader attr_name
    attr_reader attr_name+"_history"
    class_eval %Q{
      def #{attr_name}=(value)
        if(!defined?(@#{attr_name}_history))
          @#{attr_name}_history = [@#{attr_name}]
        end
 
        @#{attr_name} = value
        @#{attr_name}_history << value
      end
    }
  end
end


#Project 5
module Enumerable
  def each_with_custom_index(start, step)
    self.each_with_index do |elt, index|
      yield elt, index*step+start
    end
  end
end

#Project 6
class FibSequence
  include Enumerable
  @fibs=0
  def initialize(nr)
    @fibs=nr
  end
  def each 
    @prev=0
    @index=0
    @fibs.times do 
      if @index == 0
        yield @index=1
      else
        temp=@index
        yield @index=@prev+temp
        @prev=temp
      end
    end
  end
end

#Project 9
def each_with_flattening
  self.each do |item| 
    if item.class == Array
      item.each_with_flattening { |s| yield s }
    else
      yield item
    end
  end
end

#Project 10 
module Enumerable 
  def each_permuted
    arr_cpy = self.dup
    if self.respond_to?(:each)
      arr_cpy.sort_by { rand }
    end
  end
end

#Project 11 #Not quite sure if it works (inspired by http://stackoverflow.com/questions/12205180/implementing-binary-tree-in-ruby)
class BinaryTree
  
  attr_accessor :val

  def initialize(val=nil)
    @val = val
    @left = @right = nil
  end

  def empty? 
    @val == nil 
  end

  def << (x)
    if self.empty? 
      @val=x
    else
      test = @val <=> x
      case test
        when 1 # @val is greater
          @left = BinaryTree.new(nil)
          @left << x
        when -1, 0 # @val is less or equal
          @right = BinaryTree.new(nil)
          @right << x
      end
    end
  end

  def each 
    unless self.empty? 
      @left.each { |val| yield val }
      yield @val
      @right.each { |val| yield val }
    end
  end
end
   
#Project 13
class Numeric
  def dollars
    Float.new(self)
  end
  def euro
    self/1.3
  end
  def yen 
    self*0.012
  end
  def in(val)
    case val
    when :dollars
      self
    when :euro
      self*1.3
    when :yen
      self/0.012
    else 
      "not defined currency"
    end 
  end
end