ruby cookbook -- SortedArray

rubycook book:
Recipe 4.7. Making Sure a Sorted Array Stays Sorted

class SortedArray < Array
  def initialize(*args,&sort_by)
    @sort_by = &sort_by || Pro.new{|x,y| x <=> y}
    super(*args)
    sort! @sort_by
  def insert(i,v)
    insert_before = index(find{|x| @sort_by.call(x,y) == 1 }
    super(insert_before ? insert_before : -1,v)
  end
  def <<(v)
    insert(0,v)
  end
  alias push <<
  alias unshift <<

  ["collect!", "flatten!", "[]="].each do |method_name|
     module_eval %{
       def #{method_name}(*args)
	 super
	 sort! &@sort_by
       end
     }
  end

  def reverse!
    #Do nothing; reversing the array would disorder it.
  end
end

	class  
SortedArray
	  def []=(*args)
	    if args.size == 3
	      #e.g. "a[6,3] = [1,2,3]"
	      start, length, value = args
	      slice! Range.new(start, start+length, true)
	      (value.respond_to? :each) ? value.each { |x| self << x } : self << value
	    elsif args.size == 2
	      index, value = args
	      if index.is_a? Numeric
	        #e.g. "a[0] = 10" (the most common form of array assignment)
	        delete_at(index)
	        self << value
	      elsif index.is_a? Range
	        #e.g. "a[0..3] = [1,2,3]"
	        slice! index
	        (value.respond_to? :each) ? value.each { |x| self << x } : self << value
	      else
	        #Not supported. Delegate to superclass; will probably give an error.
	        super
	        sort!(&sort_by)
	      end
	    else
	      #Not supported. Delegate to superclass; will probably give an error.
	      super
	      sort!(&sort_by)
	    end
	  end
	end