brew/Library/Homebrew/dependencies.rb

require "delegate"

class Dependencies < DelegateClass(Array)
  def initialize(*args)
    super(args)
  end

  alias eql? ==

  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

  def inspect
    "#<#{self.class.name}: #{to_a}>"
  end
end

class Requirements < DelegateClass(Set)
  def initialize(*args)
    super(Set.new(args))
  end

  def <<(other)
    if other.is_a?(Comparable)
      grep(other.class) do |req|
        return self if req > other
        delete(req)
      end
    end
    super
    self
  end

  def inspect
    "#<#{self.class.name}: {#{to_a.join(", ")}}>"
  end
end