class Variable < Struct.new(:value)
  def to_s
    "#{value} #{self.class.to_s.downcase}s"
  end

  def inspect
    to_s
  end

  def and(other)
    current = resistance = voltage = nil

    [self, other].each do |element|
      case element
      when Ampere
        current = element.value
      when Ohm
        resistance = element.value
      when Volt
        voltage = element.value
      end
    end

    if current.nil?
      Ampere.new(voltage / resistance)
    elsif resistance.nil?
      Ohm.new(voltage / current)
    elsif voltage.nil?
      Volt.new(current * resistance)
    end
  end
end

class Ampere < Variable
end

class Ohm < Variable
end

class Volt < Variable
end