poodr2/3_45.rb at master · Try2Code/poodr2 · GitHub

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# with keyword args
class Gear
  attr_reader :chainring, :cog
  def initialize(chainring:, cog:)
    @chainring = chainring
    @cog       = cog
  end

  def gear_inches(diameter)
    ratio * diameter
  end

  def ratio
    chainring / cog.to_f
  end
  # ...
end

class Wheel
  attr_reader :rim, :tire, :gear
  def initialize(rim:, tire:, chainring:, cog:)
    @rim  = rim
    @tire = tire
    @gear = Gear.new(chainring: chainring, cog: cog)
  end

  def diameter
    rim + (tire * 2)
  end

  def gear_inches
    gear.gear_inches(diameter)
  end
  # ...
end

puts Wheel.new(
       rim:       26,
       tire:      1.5,
       chainring: 52,
       cog:       11).gear_inches
# => 137.0909090909091