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class Bicycle
  attr_reader :style, :size, :tape_color, :front_shock, :rear_shock

  def initialize(**opts)
    @style = opts[:style]
    @size = opts[:size]
    @tape_color = opts[:tape_color]
    @front_shock = opts[:front_shock]
    @rear_shock = opts[:rear_shock]
  end

  def spares
    if style == :road
    { chain: '11-speed',
      tire_size: '23',
      tape_color: tape_color }
    else
    { chain: '11-speed',
      tire_size: '2.1',
      front_shock: front_shock }
    end
  end
  # ...
end

class MountainBike < Bicycle
  attr_reader :front_shock, :rear_shock

  def initialize(**opts)
    @front_shock = opts[:front_shock]
    @rear_shock = opts[:rear_shock]
    super
  end

  def spares
    super.merge(front_shock: front_shock)
  end
end