module Enumerable

  # Same as #collect but with an iteration counter.
  #
  #   a = [1,2,3].collect_with_index { |e,i| e*i }
  #   a  #=> [0,2,6]
  #
  # CREDIT: Gavin Sinclair

  def collect_with_index
    r = []
    each_index do |i|
      r << yield(self[i], i)
    end
    r
  end

  # Alias for collect_with_index.

  alias_method :map_with_index, :collect_with_index

  # A more versitle #compact method. It can be used to
  # collect and filter items out in one single step.
  #
  #   [1,2,3].compact_map do |n|
  #     n < 1 ? nil : n
  #   end
  #
  # _produces_
  #
  #   [2,3]
  #
  # NOTE: Perhaps nicer to have as added functionality for #compact.
  #
  # CREDIT: Trans

  def compact_map(trash=nil, &block)
    y = []
    if block_given?
      each do |*a|
        r = yield(*a)
        y << r unless trash == r
      end
    else
      each do |r|
        y << r unless trash == r
      end
    end
    y
  end

  alias_method :compact_collect, :compact_map
end