# Add Array#sort_by!
class Array
  def sort_by! &block
    replace(sort_by(&block))
  end
end


class Foo
  class << self
    attr_accessor :subclasses, :priority
  end
  self.subclasses = []
  # 1 is highest, lower is low
  self.priority = 5

  def self.inherited klass
    subclasses << klass
  end

  # Call after you've loaded all subclasses, so we can sort them properly
  def self.order_subclasses
    self.subclasses.sort_by!(&:priority).reverse!
  end
end

class Bar < Foo
  self.priority = 10
end

class Sed < Foo
  self.priority = 15
end

class Fred < Foo
  self.priority = 3
end

Foo.order_subclasses
p Foo.subclasses
# should be [Sed, Bar, Fred]

# >> [Sed, Bar, Fred]