Kata Eighteen requires some code to calculate transitive dependencies, i.e. how dependencies propagate between things. Here is my solution.

class Dependencies

def initialize()
@direct = Hash.new
end

def add_direct(item, dependants)
@direct[item] = dependants
end

def dependencies_for(item)
dependants = []
toBeProcessed = @direct[item].clone
while not toBeProcessed.empty?
x = toBeProcessed.shift
if x != item and not dependants.include?(x)
dependants << x toBeProcessed.concat(@direct[x]) if @direct.include?(x) end end return dependants.sort! end end [/sourcecode]