about = <<'ABOUT'

This is quite a long example in which we define a class,
and several subclasses. I've added it here because it shows
the use of a static (class) variable @@numtrains, and a static
(class) method getnt, which is called on the class and not on
individual object members of the class.

ABOUT

class Transport
        @@numtrains = 0
        def initialize(seats,standees = 0)
                @bumholders = seats
                @suckers = standees
                @@numtrains += 1
        end
        def getloadfactor()
                return @bumholders + @suckers
        end
        def self.getnt()
                # Can only refer to class variables
                # Could write Transport.getnt instead (Yuk!)
                return @@numtrains
        end
end

class Train < Transport
        def grumble()
                @suckers -= 7
        end
end
class Bus < Transport
        def initialize(route,seats,standees = 0)
                super(seats,standees+1)
                @route = route
        end
        def grumble()
                @suckers /= 2
        end
end

if __FILE__ == $0
        barking_train = Train.new(180,400)
        newquay_train = Train.new(458,60)
        stratford_bus = Bus.new("1A",70,65)
        stonehenge = Bus.new(3,120,8)

        pubtrans = [barking_train, newquay_train,
                stratford_bus, stonehenge ]

        pubtrans.each do | thomas |
                thomas.grumble()
                crushval = thomas.getloadfactor()
                puts crushval
        end
        puts "There are #{Transport::getnt} transport pieces"
        puts "There are #{Transport.getnt} transport pieces"
end

__END__

92:sqs grahamellis$ ruby obtest.rb
573
511
103
124
There are 4 transport pieces
There are 4 transport pieces
92:sqs grahamellis$