- Introduction
- Introducing Ruby
- Having Some Fun with Ruby
- Where Next?
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Having Some Fun with Ruby
Writing single classes, although instructive, is just part of a bigger picture. Useful software arises from the interaction of many different objects, and so to illustrate this the CircularCounter class will be used to create an Odometer. Just for fun, the Odometer will be configurable as to which number base it will use, and each wheel on the Odometer will be represented by a kind of CircularCounter. Like all toy problems, this design could be drastically improved, but it demonstrates inheritance and some of the more esoteric functionality of the Array class.
The first thing to do is save the definition of the CircularCounter class in a file called CircularCounter.rb, and then create an OdometerWheel.rb file containing the following definition:
class OdometerWheel < CircularCounter def initialize (limit, initialValue, nextWheel) super (limit,initialValue) #invoke parent constructor @nextWheel = nextWheel end def increment if (super) #invoke superclass version of increment nextWheel.increment end end end
Once that's in place, the Odometer class itself is relatively simple to create (in Odometer.rb), even if the collect! idiom does require a bit of thought and a scan through the Array documentation:
class Odometer
def initialize(size,base)
@wheels = Array.new(size)
@wheels[0] = CircularCounter.new(base,0)
prev = @wheels[0]
@wheels.collect! { |elem|
if (nil == elem)
elem = OdometerWheel.new(base,0,prev)
prev = elem
else
elem = prev
end
}
end
def increment
@wheels.last.increment
end
def reading
val =""
@wheels.each{|elem| val = val + elem.value.to_s }
val
end
end
Once this is in place, a simple test script can validate that everything is working as expected:
require "CircularCounter.rb"
require "OdometerWheel.rb"
require "Odometer.rb"
# decimal Odometer
o = Odometer.new (6,10)
12345.times { o.increment }
p o.reading
# Binary odometer
bin = Odometer.new (8,2)
32.times { bin.increment }
p bin.reading
With this script in a file called OdometerTest.rb, it can be executed directly in interactive Ruby:
D:\Ruby\bin>ruby irb irb(main):001:0> require "OdometerTest.rb" "012345" "00100000" true irb(main):002:0> exit
The script can also be run as a normal Ruby script:
D:\Ruby\bin>ruby OdometerTest.rb "012345" "00100000" D:\Ruby\bin>