inherited.rb

class ShippingOption   # Base class
  @children = []  
  def self.inherited(child)
    @children << child
  end
  def self.shipping_options(weight, international)
    @children.select {|child| child.can_ship?(weight, international)}
  end
end

class MediaMail < ShippingOption
  def self.can_ship?(weight, international)
    !international
  end
end

class FlatRatePriorityEnvelope < ShippingOption
  def self.can_ship?(weight, international)
    weight < 64 && !international
  end
end
  
class InternationalFlatRateBox < ShippingOption
  def self.can_ship?(weight, international)
    weight >= 64 && weight < 9*16 && international
  end
end
       
puts "Shipping 16oz domestic"
puts ShippingOption.shipping_options(16, false)

puts "\nShipping 90oz domestic"
puts ShippingOption.shipping_options(90, false)

puts "\nShipping 16oz international"
puts ShippingOption.shipping_options(16, true)