Teaching Ruby to Count

Ruby has some of the best tooling in the business for working with iteration and data series. By leveraging its full power, you can build delightful interfaces for your objects.

In this case-study based presentation, we’ll explore a variety of problems such as composing Enumerable methods, generating a series of custom objects, and how to provide a clean interface for a collection with multiple valid traversal orders. Beyond just the beloved Enumerable module, this talk will take you into the world of Enumerators and Ranges and equip you to write objects that bring joy to your teammates.

Originally given at RubyConf Mini 2022. Video can be viewed at https://www.youtube.com/watch?v=PHMOsTK1jSE

Transcript

6. for ($i=0; $i<3; $i++) { echo "hello"; }
7. for ($i=0; $i < $array.length; $i++) { echo $array[$i]; }
8. $result = []; for ($i=0; $i<$array.length; $i++) { if ($array[$i] % 2 == 0) { $result[] = $array[$i]; } } return $result;
10. 3.times do puts "hello" end
11. array.each do |item| puts item end
12. array.select do |n| n.even? end
19. (5..7).each do |n| puts n end # 5 # 6 # 7
21. march = Date.new(2022, 3) sept = Date.new(2022, 9) (march..sept).each do |date| # ... end # March 1, March 2, March 3, ...
22. (march..sept).select do |date| date.day == 1 end.each do |date| # ... end # March 1, April 1, May 1, ...
25. class Month def initialize(months) @months = months end end
26. class Month def self.from_parts(year, months) new (year * 12) + months end end
27. march = Month.from_parts(2022, 3) sept = Month.from_parts(2022, 9) (march..sept).each do |month| # ... end # ArgumentError: bad value for range
31. class Month def <=>(other) months <=> other.months end end
32. class Month def succ Month.new(months.succ) end end
33. march = Month.from_parts(2022, 3) sept = Month.from_parts(2022, 9) (march..sept).each do |month| # ... end # March 2022, April 2022, May 2022, ...
44. class CompositeFile def initialize(files) @files = files end end
45. monte_cristo = CompositeFile.new(chapters) monte_cristo.find { |line| line.include? "Villefort" } # Undefined method `find` for CompositeFile
48. def each @files.each do |file| file.each do |line| yield line end end end
49. monte_cristo.each do |line| puts line end
51. class CompositeFile include Enumerable # ... end
52. monte_cristo.find do |line| line.include? "Villefort" end # => "“Could you ever have credited such a thing, my dear Danglars?” asked M. Morrel, as, on his return to the port for the purpose of gleaning fresh tidings of Dantès, from M. de Villefort, the assistant procureur, he overtook his supercargo and Caderousse."
56. array.each_with_index(1) do |item, index| puts "#{index}. #{item}" end
58. array.map.with_index(1) do |item, index| "#{index}. #{item}" end # => ["1. first", "2. second", ... ]
59. array = [1, 2, 3] array.cycle(3).with_index(1).select do |item, index| index.even? && item.even? end # => [[2, 2], [2, 8]]
61. [1, 2, 3].map # => #<Enumerator: ...>
64. 3.times #=> #<Enumerator: ...> 5.upto(10) #=> #<Enumerator: ...> [1, 2, 3].each #=> #<Enumerator: ...>
69. enum = [1, 2].to_enum(:each) enum.next # => 1 enum.next # 2 enum.next # raise StopIteration
71. percentages = Enumerator.produce { rand(100) } percentages.next # => 7 percentages.next # => 51
74. numbers = [1, 2, 3].cycle numbers.take(4) # => [1, 2, 3, 1]
77. class CompositeBook include Enumerable def each # by line end def each # by word end end
78. class CompositeBook def each_line # ... end def each_word # ... end end
79. class CompositeBook def each_line return to_enum(:each_line) unless block_given # actual looping end end
80. monte_cristo.each_line.find { |line| ... } monte_cristo.each_word.map { |word| ... }