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Better Object-Oriented Design Through... Tail-Call Optimization?
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# Abstract UnionList base class | |
class AbstractUnionList | |
private :initialize | |
def length | |
how_many?(0) | |
end | |
def how_many?(counter) | |
raise NotImplementedError | |
end | |
end | |
# UnionList NullObject | |
class NullUnionList < AbstractUnionList | |
public :initialize | |
def how_many?(counter) | |
counter | |
end | |
end | |
# How one might intuitively implement UnionList | |
class UnionList < AbstractUnionList | |
attr_reader :adjoining | |
def initialize(adjoining) | |
@adjoining = adjoining | |
end | |
def how_many?(counter) | |
adjoining.how_many?(counter + 1) | |
end | |
end | |
# OO-design violating work around for SystemStackError | |
class IterativeUnionList < UnionList | |
def how_many?(counter) | |
remaining = self | |
count = 0 | |
# Shouldn't have to know anything about NullUnionList :( | |
while !remaining.is_a?(NullUnionList) | |
count += 1 | |
remaining = remaining.adjoining | |
end | |
count | |
end | |
end | |
# OO-design friendly and it works? Still my beating heart! | |
require "tco_method" | |
class TCOUnionList < UnionList | |
extend TCOMethod::Mixin | |
tco_method :how_many? | |
end | |
# A class to test each of the UnionList implementations | |
class UnionListTest | |
def test(class_under_test, length) | |
last = NullUnionList.new | |
length.times { last = class_under_test.new(last) } | |
msg = "class_under_test=#{class_under_test.name} length=#{length} result=" | |
msg.concat(last.length == length ? "Success" : "Fail") | |
puts(msg) | |
rescue StandardError, SystemStackError => e | |
puts msg.concat("Fail error=#{e.class}") | |
end | |
end | |
# Let the testing begin! | |
test_case = UnionListTest.new | |
classes_to_test = [ | |
UnionList, | |
IterativeUnionList, | |
TCOUnionList, | |
] | |
divider = "-----------------" | |
puts divider | |
# Test lists of length 1..10000 | |
5.times do |pow| | |
length = 10 ** pow | |
classes_to_test.each do |class_under_test| | |
test_case.test(class_under_test, length) | |
end | |
puts divider | |
end | |
# ----------------- | |
# class_under_test=UnionList length=1 result=Success | |
# class_under_test=IterativeUnionList length=1 result=Success | |
# class_under_test=TCOUnionList length=1 result=Success | |
# ----------------- | |
# class_under_test=UnionList length=10 result=Success | |
# class_under_test=IterativeUnionList length=10 result=Success | |
# class_under_test=TCOUnionList length=10 result=Success | |
# ----------------- | |
# class_under_test=UnionList length=100 result=Success | |
# class_under_test=IterativeUnionList length=100 result=Success | |
# class_under_test=TCOUnionList length=100 result=Success | |
# ----------------- | |
# class_under_test=UnionList length=1000 result=Success | |
# class_under_test=IterativeUnionList length=1000 result=Success | |
# class_under_test=TCOUnionList length=1000 result=Success | |
# ----------------- | |
# class_under_test=UnionList length=10000 result=Fail error=SystemStackError | |
# class_under_test=IterativeUnionList length=10000 result=Success | |
# class_under_test=TCOUnionList length=10000 result=Success | |
# ----------------- |
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