class MyCapacity
include Comparable
attr :volume
def initialize(volume) # 0..9
@volume = volume
end
def inspect
'#' * @volume
end
def <=>(other)
self.volume <=> other.volume
end
def succ
raise(IndexError, "Volume too big") if @volume >= 9
MyCapacity.new(@volume.succ)
end
end
medium_volume = MyCapacity.new(4)..MyCapacity.new(7)
medium_volume.to_a
medium_volume.include?(MyCapacity.new(3))
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