class Array

  # The class for the "floe" object that constructed by
  # Array#each_with_floe and Array#each_with_index_floe
  class FirstLastOddEven
    def initialize(i, size) # :nodoc:
      @first = i == 0
      @last = i == size -1
      @odd = i.odd?
    end
    
    # Returns true for the first element
    def first? 
      @first
    end
    
    # Returns true for the last element
    def last?
      @last
    end

    # Returns true for odd-numbered elements
    def odd?
      @odd
    end

    # Returns true for even-numbered elements
    def even?
      !@odd
    end

    # Returns a space-separated list of "first", "last", "odd", and "even"
    # as appropriate for the current element.
    def to_s
      @str ||= [@first && "first", @last && "last", @odd ? "odd" : "even"].select{|x| x}.join(' ')
    end
  end

  # For each element in the array, calls the block with two arguments: the
  # element and a "floe" object.
  #
  #    ary.each_with_floe do |element, floe|
  #      if floe.first?
  #          puts "#{element} is the first element"
  #      end
  #      if floe.last?
  #          puts "#{element} is the last element"
  #      end
  #      if floe.odd?
  #          puts "#{element} is an odd-numbered element"
  #      end
  #      if floe.even?
  #          puts "#{element} is an even-numbered element"
  #      end
  #  end
  #
  # If no block is given, an enumerator is returned instead.
  def each_with_floe() # :yields: element, floe
    if block_given?
      each_with_index do |element, i|
        yield(element, FirstLastOddEven.new(i, size))
      end
    else
      Enumerable::Enumerator.new(self, :each_with_floe)
    end
  end
  
  # For each element in the array, calls the block with three arguments: the
  # element, its index, and a "floe" object.
  #
  #   ary.each_with_index_floe do |element, i, floe|
  #       assert_equal(i == 0,        floe.first?)
  #       assert_equal(i == ary.last, floe.last?)
  #       assert_equal(i % 2 == 1,    float.odd?)
  #       assert_equal(i % 2 == 1,    float.even?)
  #   end
  #
  # If no block is given, an enumerator is returned instead.
  def each_with_index_floe() # :yields: element, i, floe
    if block_given?
      each_with_index do |element, i|
        yield(element, i, FirstLastOddEven.new(i, size))
      end
    else
      Enumerable::Enumerator.new(self, :each_with_index_floe)
    end
  end
end