class Array
  class << self
    # Standard in Ruby 1.9. See official documentation[http://ruby-doc.org/core-1.9/classes/Array.html]
    def try_convert(x)
      x.to_ary if x.respond_to? :to_ary
    end unless method_defined? :try_convert
  end

  # Standard in Ruby 1.9. See official documentation[http://ruby-doc.org/core-1.9/classes/Array.html]
  make_block_optional :collect!, :map!, :each, :each_index, :reverse_each, :reject, :reject!, :delete_if, :test_on => [42]
  
  # Standard in Ruby 1.9. See official documentation[http://ruby-doc.org/core-1.9/classes/Array.html]
  def combination(num)
    num = num.to_i
    return to_enum(:combination, num) unless block_given?
    return self unless (0..size).include? num
    # Implementation note: slightly tricky.
                                             # Example: self = 1..7, num = 3
    picks = (0...num).to_a                   # picks start at 0, 1, 2
    max = ((size-num)...size).to_a           # max (index for a given pick) is [4, 5, 6]
    pick_max_pairs = picks.zip(max).reverse  # pick_max_pairs = [[2, 6], [1, 5], [0, 4]]
    lookup = pick_max_pairs.find(Proc.new{return self})
    loop do
      yield values_at(*picks)
      move = lookup.each{|pick, max| picks[pick] < max}.first
      new_index = picks[move] + 1
      picks[move...num] = (new_index...(new_index+num-move)).to_a
    end
  end unless method_defined? :combination
  
  # Standard in Ruby 1.9. See official documentation[http://ruby-doc.org/core-1.9/classes/Array.html]
  def cycle(*arg, &block)
    return to_enum(:cycle, *arg) unless block_given?
    nb = arg.empty? ? (1/0.0) : arg.first
    nb.to_i.times{each(&block)}
  end unless method_defined? :cycle
  
  # extract_options! in backports.rb
  
  # flatten & flatten!, standard in ruby 1.9. See official documentation[http://ruby-doc.org/core-1.9/classes/Array.html]
  unless ([[]].flatten(1) rescue false)

    # Recursively flatten any contained Arrays into an one-dimensional result.
    # Adapted from rubinius'
    def flatten_with_optional_argument(level=nil)
      return flatten_without_optional_argument unless level || level == (1/0.0)
      dup.flatten!(level) || self
    end

    # Flattens self in place as #flatten. If no changes are
    # made, returns nil, otherwise self.
    # Adapted from rubinius'
    def flatten_with_optional_argument!(level=nil)
      return flatten_without_optional_argument! unless level || level == (1/0.0)
      
      ret, out = nil, []
      ret = recursively_flatten_finite(self, out, level)
      replace(out) if ret
      ret
    end

    alias_method_chain :flatten, :optional_argument
    alias_method_chain :flatten!, :optional_argument

    # Helper to recurse through flattening
    # Adapted from rubinius'; recursion guards are not needed because level is finite
    def recursively_flatten_finite(array, out, level)
      ret = nil
      if level <= 0
        out.concat(array)
      else
        array.each do |o|
          if o.respond_to? :to_ary
            recursively_flatten_finite(o.to_ary, out, level - 1)
            ret = self
          else
            out << o
          end
        end
      end
      ret
    end
    private :recursively_flatten_finite
  end # flatten & flatten!
  
  # index
  unless ([1].index{true} rescue false)
    def index_with_block(*arg)
      return index_without_block(*arg) unless block_given? && arg.empty?
      each_with_index{|o,i| return i if yield o}
      return nil
    end
    alias_method_chain :index, :block
    alias_method :find_index, :index
  end
  
  # pop. Standard in Ruby 1.9. See official documentation[http://ruby-doc.org/core-1.9/classes/Array.html]
  unless ([1].pop(1) rescue false)
    def pop_with_optional_argument(*arg)
      return pop_without_optional_argument if arg.empty?
      n = arg.first.to_i
      slice!([0,size-n].max, size)
    end
    alias_method_chain :pop, :optional_argument
  end
  
  def product(*arg)
    arrays = [self, *arg].reverse
    first_enum = Enumerator.new{|yielder| yielder.yield [] }
    arrays.inject(first_enum) do |enum, array|
      Enumerator.new do |yielder|
        array.each do |obj|
          enum.each do |partial_product|
            yielder.yield [obj] + partial_product
          end
        end
      end
    end.to_a
  end unless method_defined? :product

  # rindex
  unless ([1].rindex{true} rescue false)
    def rindex_with_block(*arg)
      return rindex_without_block(*arg) unless block_given? && arg.empty?
      reverse_each.each_with_index{|o,i| return size - 1 - i if yield o}
      return nil
    end
    alias_method_chain :rindex, :block
  end
  
  # shift. Standard in Ruby 1.9. See official documentation[http://ruby-doc.org/core-1.9/classes/Array.html]
  unless ([1].shift(1) rescue false)
    def shift_with_optional_argument(*arg)
      return shift_without_optional_argument if arg.empty?
      n = arg.first.to_i
      slice!(0, n)
    end
    alias_method_chain :shift, :optional_argument
  end
  
  
  def sample(*arg)
    return self[rand(size)] if arg.empty?
    n = [arg.first.to_i, size].min
    index = Array.new(size)
    n.times do |i|
      r = i + rand(size - i)
      index[i], index[r] = index[r] || r, index[i] || i
    end
    values_at(*index.first(n))
  end unless method_defined? :sample
  
  def shuffle
    sample(size)
  end unless method_defined? :shuffle

  def shuffle!
    replace(sample(size))
  end unless method_defined? :shuffle!

end