brew/Library/Homebrew/dependencies.rb

class Dependencies
  include Enumerable

  def initialize(*args)
    @deps = Array.new(*args)
  end

  def each(*args, &block)
    @deps.each(*args, &block)
  end

  def <<(o)
    @deps << o unless @deps.include? o
    self
  end

  def empty?
    @deps.empty?
  end

  def *(arg)
    @deps * arg
  end

  def to_a
    @deps
  end
  alias_method :to_ary, :to_a

  def optional
    select(&:optional?)
  end

  def recommended
    select(&:recommended?)
  end

  def build
    select(&:build?)
  end

  def required
    select(&:required?)
  end

  def default
    build + required + recommended
  end
end