Katrina Owen_One small-step_Codemotion Berlin 2019

Refactoring sometimes devolves into an appalling mess. You're chasing a broken test suite, and every change just makes it worse. At other times it's a slow, controlled process culminating in dreadful design. This talk presents an end-to-end refactoring that demonstrates simple strategies to avoid such misadventures.

About:
Katrina Owen, Senior Software Engineer - GitHub

Katrina is an engineer at GitHub. She accidentally became a developer while pursuing a degree in molecular biology. When programming, her focus is on automation, workflow optimization, and refactoring. She works primarily in Go and Ruby, contributes to several open source projects, and is the creator of exercism.io, a platform for code practice and programming mentorship.

Transcript

1. small one step KATRINA OWEN · GITHUB · @KYTRINYX
2. A refactoring story.
3. I know an old lady who swallowed a fly.
4. She swallowed the spider to catch the fly. I know an old lady who swallowed a spider.
5. She swallowed the bird to catch the spider. She swallowed the spider to catch the fly. I know an old lady who swallowed a bird.
6. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider. She swallowed the spider to catch the fly. I know an old lady who swallowed a cat.
7. She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider. She swallowed the spider to catch the fly. I know an old lady who swallowed a dog.
8. She swallowed the goat to catch the dog. She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider. She swallowed the spider to catch the fly. I know an old lady who swallowed a goat.
9. She swallowed the cow to catch the goat. She swallowed the goat to catch the dog. She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider. She swallowed the spider to catch the fly. I know an old lady who swallowed a cow.
10. I know an old lady who swallowed a horse.
11. She’s dead of course. I know an old lady who swallowed a horse.
12. We've all done it.
13. It's wasteful.
14. How to not do that.
15. An algorithmic song.
16. Ignore the Ruby.
17. I know an old lady who swall Imagine that, to swallow a c She swallowed the cat to cat She swallowed the bird to ca She swallowed the spider to I don't know why she swallow
18. I know an old lady who swallowed a fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a spider. It wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a bird. How absurd to swallow a bird! She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a cat. Imagine that, to swallow a cat! She swallowed the cat to catch the bird. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a dog. What a hog, to swallow a dog! She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a goat. Just opened her throat and swallowed a goat! She swallowed the goat to catch the dog. She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a cow. I don't know how she swallowed a cow! She swallowed the cow to catch the goat. She swallowed the goat to catch the dog. She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a horse. She's dead, of course!
19. I know an old lady who swallowed a fly. # ... She's dead, of course!
20. <<~SONG I know an old lady who swallowed a fly. # ... She's dead, of course! SONG
21. def lyrics <<~SONG I know an old lady who swallowed a fly. # ... She's dead, of course! SONG end
22. class Song def lyrics <<~SONG I know an old lady who swallowed a fly. # ... She's dead, of course! SONG end end
23. Why do we refactor?
24. Not about aesthetics.
25. Change is coming.
31. A new implementation?
32. class Song def lyrics <<~SONG I know an old lady who swallowed a fly. # ... She's dead of course. SONG end end
33. <<~SONG I know an old lady who swallowed a fly. # ... She's dead of course. SONG
34. expected = <<~SONG I know an old lady who swallowed a fly. # ... She's dead of course. SONG
35. expected = <<~SONG I know an old lady who swallowed a fly. # ... She's dead of course. SONG assert_equal expected, Song.new.lyrics
36. A characterization test.
37. And so it begins.
38. <<~SONG I know an old lady who swallowed a fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a spider. It wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a bird. How absurd to swallow a bird! She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a cat. Imagine that, to swallow a cat! She swallowed the cat to catch the bird. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a dog. What a hog, to swallow a dog! She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a goat. Just opened her throat and swallowed a goat! She swallowed the goat to catch the dog. She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a cow. I don't know how she swallowed a cow! She swallowed the cow to catch the goat. She swallowed the goat to catch the dog. She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a horse. She's dead, of course! SONG
39. I know an old lady who swallowed a dog. What a hog, to swallow a dog! She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider... She swallowed the spider to catch the fly. I don't know why she swallowed the fly...
40. I know an old lady who swallowed a cat... I know an old lady who swallowed a dog... I know an old lady who swallowed a goat...
41. 1. How to construct a verse. 2. How to string verses together. 3. Support for arbitrary creatures.
42. case i when 1 # ... when n # ... end
43. (1..8).map {|i| case i when 1 # ... when n # ... end }.join("\n")
44. def verse(i) case i when 1 # ... when n # ... end end
45. case i when 1 "I know an old lady who swallowed a fly.\n" + "I don't know why she swallowed the fly. Perhaps she'l when 2 "I know an old lady who swallowed a spider.\n" + "It wriggled and jiggled and tickled inside her.\n" + "She swallowed the spider to catch the fly.\n" + "I don't know why she swallowed the fly. Perhaps she'l when 3 "I know an old lady who swallowed a bird.\n" + "How absurd to swallow a bird!\n" + "She swallowed the bird to catch the spider that wrigg "She swallowed the spider to catch the fly.\n" + "I don't know why she swallowed the fly. Perhaps she'l
46. case i when 1 "I know an old lady who swallowed a %s.\n" % "fly" + "%s\n" % "I don't when 2 "I know an old lady who swallowed a %s.\n" % "spider" "%s\n" % "It wrigg "She swallowed the %s to catch the %s.\n" % ["spider" "%s\n" % "I don't when 3 "I know an old lady who swallowed a %s.\n" % "bird" + "%s\n" % "How absu "She swallowed the %s to catch the %s.\n" % ["bird", "She swallowed the %s to catch the %s.\n" % ["spider" "%s\n" % "I don't
47. "I know an old lady who swallowed a %s.\n" % "%s\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "%s\n" %
48. % "cow" + % "I don't know how she swallowed a cow!" + % ["cow", "goat"] + % ["goat", "dog"] + % ["dog", "cat"] + % ["cat", "bird"] + % ["bird", "spider that wriggled and..."] + % ["spider", "fly"] + % "I don't know why she..."
49. <<~SONG I know an old lady who swallowed a fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a spider. It wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a bird. How absurd to swallow a bird! She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a cat. Imagine that, to swallow a cat! She swallowed the cat to catch the bird. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a dog. What a hog, to swallow a dog! She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a goat. Just opened her throat and swallowed a goat! She swallowed the goat to catch the dog. She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a cow. I don't know how she swallowed a cow! She swallowed the cow to catch the goat. She swallowed the goat to catch the dog. She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly. I don't know why she swallowed the fly. Perhaps she'll die. I know an old lady who swallowed a horse. She's dead, of course! SONG
50. case i when 1 "I know an old lady who swallowed a fly.\n" + "I don't know why she swallowed the fly. Perhaps she'll die.\n" when 2 "I know an old lady who swallowed a spider.\n" + "It wriggled and jiggled and tickled inside her.\n" + "She swallowed the spider to catch the fly.\n" + "I don't know why she swallowed the fly. Perhaps she'll die.\n" when 3 "I know an old lady who swallowed a bird.\n" + "How absurd to swallow a bird!\n" + "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" + "She swallowed the spider to catch the fly.\n" + "I don't know why she swallowed the fly. Perhaps she'll die.\n" when 4 "I know an old lady who swallowed a cat.\n" + "Imagine that, to swallow a cat!\n" + "She swallowed the cat to catch the bird.\n" + "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" + "She swallowed the spider to catch the fly.\n" + "I don't know why she swallowed the fly. Perhaps she'll die.\n" when 5 "I know an old lady who swallowed a dog.\n" + "What a hog, to swallow a dog!\n" + "She swallowed the dog to catch the cat.\n" + "She swallowed the cat to catch the bird.\n" + "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" + "She swallowed the spider to catch the fly.\n" + "I don't know why she swallowed the fly. Perhaps she'll die.\n" when 6 "I know an old lady who swallowed a goat.\n" + "Just opened her throat and swallowed a goat!\n" + "She swallowed the goat to catch the dog.\n" + "She swallowed the dog to catch the cat.\n" + "She swallowed the cat to catch the bird.\n" + "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" + "She swallowed the spider to catch the fly.\n" + "I don't know why she swallowed the fly. Perhaps she'll die.\n" when 7 "I know an old lady who swallowed a cow.\n" + "I don't know how she swallowed a cow!\n" + "She swallowed the cow to catch the goat.\n" + "She swallowed the goat to catch the dog.\n" + "She swallowed the dog to catch the cat.\n" + "She swallowed the cat to catch the bird.\n" + "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n" + "She swallowed the spider to catch the fly.\n" + "I don't know why she swallowed the fly. Perhaps she'll die.\n" when 8 "I know an old lady who swallowed a horse.\n" + "She's dead, of course!\n" end
51. case i when 1 "I know an old lady who swallowed a %s.\n" % "fly" + "%s\n" % "I don't know why she swallowed the fly. Perhaps she'll die." when 2 "I know an old lady who swallowed a %s.\n" % "spider" + "%s\n" % "It wriggled and jiggled and tickled inside her." + "She swallowed the %s to catch the %s.\n" % ["spider", "fly"] + "%s\n" % "I don't know why she swallowed the fly. Perhaps she'll die." when 3 "I know an old lady who swallowed a %s.\n" % "bird" + "%s\n" % "How absurd to swallow a bird!" + "She swallowed the %s to catch the %s.\n" % ["bird", "spider that wriggled and jiggled and tickled inside her"] + "She swallowed the %s to catch the %s.\n" % ["spider", "fly"] + "%s\n" % "I don't know why she swallowed the fly. Perhaps she'll die." when 4 "I know an old lady who swallowed a %s.\n" % "cat" + "%s\n" % "Imagine that, to swallow a cat!" + "She swallowed the %s to catch the %s.\n" % ["cat", "bird"] + "She swallowed the %s to catch the %s.\n" % ["bird", "spider that wriggled and jiggled and tickled inside her"] + "She swallowed the %s to catch the %s.\n" % ["spider", "fly"] + "%s\n" % "I don't know why she swallowed the fly. Perhaps she'll die." when 5 "I know an old lady who swallowed a %s.\n" % "dog" + "%s\n" % "What a hog, to swallow a dog!" + "She swallowed the %s to catch the %s.\n" % ["dog", "cat"] + "She swallowed the %s to catch the %s.\n" % ["cat", "bird"] + "She swallowed the %s to catch the %s.\n" % ["bird", "spider that wriggled and jiggled and tickled inside her"] + "She swallowed the %s to catch the %s.\n" % ["spider", "fly"] + "%s\n" % "I don't know why she swallowed the fly. Perhaps she'll die." when 6 "I know an old lady who swallowed a %s.\n" % "goat" + "%s\n" % "Just opened her throat and swallowed a goat!" + "She swallowed the %s to catch the %s.\n" % ["goat", "dog"] + "She swallowed the %s to catch the %s.\n" % ["dog", "cat"] + "She swallowed the %s to catch the %s.\n" % ["cat", "bird"] + "She swallowed the %s to catch the %s.\n" % ["bird", "spider that wriggled and jiggled and tickled inside her"] + "She swallowed the %s to catch the %s.\n" % ["spider", "fly"] + "%s\n" % "I don't know why she swallowed the fly. Perhaps she'll die." when 7 "I know an old lady who swallowed a %s.\n" % "cow" + "%s\n" % "I don't know how she swallowed a cow!" + "She swallowed the %s to catch the %s.\n" % ["cow", "goat"] + "She swallowed the %s to catch the %s.\n" % ["goat", "dog"] + "She swallowed the %s to catch the %s.\n" % ["dog", "cat"] + "She swallowed the %s to catch the %s.\n" % ["cat", "bird"] + "She swallowed the %s to catch the %s.\n" % ["bird", "spider that wriggled and jiggled and tickled inside her"] + "She swallowed the %s to catch the %s.\n" % ["spider", "fly"] + "%s\n" % "I don't know why she swallowed the fly. Perhaps she'll die." when 8 "I know an old lady who swallowed a %s.\n" % "horse" + "%s\n" % "She's dead, of course!" end
52. Why bother?
53. case i when 1 "I know an old lady who swallowed a %s.\n" % "%s\n" %
54. case i when 2 "I know an old lady who swallowed a %s.\n" % "%s\n" % "She swallowed the %s to catch the %s.\n" % "%s\n" %
55. case i when 3 "I know an old lady who swallowed a %s.\n" % "%s\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "%s\n" %
56. case i when 4 "I know an old lady who swallowed a %s.\n" % "%s\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "%s\n" %
57. case i when 5 "I know an old lady who swallowed a %s.\n" % "%s\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "%s\n" %
58. case i when 6 "I know an old lady who swallowed a %s.\n" % "%s\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "%s\n" %
59. case i when 7 "I know an old lady who swallowed a %s.\n" % "%s\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "She swallowed the %s to catch the %s.\n" % "%s\n" %
60. case i when 8 "I know an old lady who swallowed a %s.\n" % "%s\n" %
61. "She swallowed the %s to catch the %s."
62. "She swallowed the %s to catch the %s." % [ predator, prey, ]
63. def reasoning(predator, prey) "She swallowed the %s to catch the %s." % [ predator, prey, ] end
64. def why(predator, prey) "She swallowed the %s to catch the %s." % [ predator, prey, ] end
65. def motivation(predator, prey) "She swallowed the %s to catch the %s." % [ predator, prey, ] end
66. ["cow", "goat"] ["goat", "dog"] ["dog", "cat"] ["cat", "bird"] ["bird", "spider"] ["spider", "fly"]
67. ["cow", "goat"] ["goat", "dog"] ["dog", "cat"] ["cat", "bird"] ["bird", "spider"] ["spider", "fly"]
68. ["cow", "goat"] ["goat", "dog"] ["dog", "cat"] ["cat", "bird"] ["bird", "spider"] ["spider", "fly"]
69. ["cow", "goat"] ["goat", "dog"] ["dog", "cat"] ["cat", "bird"] ["bird", "spider"] ["spider", "fly"]
70. ["cow", "goat"] ["goat", "dog"] ["dog", "cat"] ["cat", "bird"] ["bird", "spider"] ["spider", "fly"]
71. ["cow", "goat"] ["goat", "dog"] ["dog", "cat"] ["cat", "bird"] ["bird", "spider"] ["spider", "fly"]
72. ["cow", "goat", "dog", "cat", "bird", "spider", "fly"]
73. critters = [ "cow", "goat", "dog", "cat", "bird", "spider", "fly", ]
74. critters.each_cons(2).map {|pair| motivation(*pair) }.join("\n")
75. def sequence critters.each_cons(2).map {|pair| motivation(*pair) }.join("\n") end
76. def chain critters.each_cons(2).map {|pair| motivation(*pair) }.join("\n") end
77. Trade-offs.
78. "She swallowed the cow to catch the goat.\n" + "She swallowed the goat to catch the dog.\n" + "She swallowed the dog to catch the cat.\n" + "She swallowed the cat to catch the bird.\n" + "She swallowed the bird to catch the spider.\n" + "She swallowed the spider to catch the fly.\n" +
79. def chain critters.each_cons(2).map {|pair| motivation(*pair) }.join("\n") end def motivation(predator, prey) "She swallowed the %s to catch the %s." % [ predator, prey, ] end
80. Mindless simplicity.
81. Meaningful complexity.
82. Parallel implementation.
83. "She swallowed the spider to catch the fly.\n" +
84. chain +
85. Nope.
86. Revert on failure.
87. So small you don't care.
88. def chain critters.each_cons(2).map {|pair| motivation(*pair) }.join("\n") end
89. def chain critters.each_cons(2).map {|pair| motivation(*pair) }.join("\n") end
90. def chain(i) critters.last(i).each_cons(2).map {|pair| motivation(*pair) }.join("\n") end
91. chain(2) +
92. "She swallowed the spider to catch the fly.\n" + "She swallowed the bird to catch the spider...\n" +
93. chain(3) +
94. Nope.
95. She swallowed the bird to catch the spider. She swallowed the spider to catch the fly.
96. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly.
97. She swallowed the cow to catch the goat. She swallowed the goat to catch the dog. She swallowed the dog to catch the cat. She swallowed the cat to catch the bird. She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her. She swallowed the spider to catch the fly.
98. A step back (again).
99. if prey == "spider" # ... else # ... end
100. 1. Conditionals are about differences.
101. if prey == "spider" "She swallowed [...] that wriggled [...]." else "She swallowed [...]." end
102. if prey == "spider" "She swallowed [...] that wriggled [...]." else "She swallowed [...]." end
103. if prey == "spider" "She swallowed [...] that wriggled [...]." else "She swallowed [...]." end
104. if prey == "spider" " that wriggled [...]" else ??? end
105. if prey == "spider" " that wriggled [...]" end
106. 1. Conditionals are about differences. 2. The differences represent one idea.
107. if prey == "spider" " that wriggled..." else "" end
108. def distinctive_features if prey == "spider" " that wriggled..." else "" end end
109. def qualifier if prey == "spider" " that wriggled..." else "" end end
110. if prey == "spider" " that wriggled..." end
111. def spider_tag if prey == "spider" " that wriggled..." end end
112. def spider_tag if prey == "crab" " that scurried..." end end
113. Names shape reality.
114. def qualifier if prey == "spider" " that wriggled..." else "" end end
115. def qualifier(prey) if prey == "spider" " that wriggled..." else "" end end
116. def qualifier(critter) if critter == "spider" " that wriggled..." else "" end end
117. critters = [ "cow", "goat", "dog", "cat", "bird", "spider", "fly", ]
118. qualifier(critter)
119. critter.qualifier
120. This is the turning point.
121. DATA = [ ["horse", "", "She's dead, of course!"], ["cow", "", "I don't know how..."], ["goat", "", "Just opened her throat..."], ["dog", "", "What a hog, to swallow a dog!"], ["cat", "", "Imagine that, to swallow a cat!"], ["bird", "", "How absurd to swallow a bird!"], ["spider", "that wriggled...", "It wriggled..."], ["fly", "", "I don't know why..."], ]
122. DATA = [ ["horse", "", "She's dead, of course!"], ["cow", "", "I don't know how..."], ["goat", "", "Just opened her throat..."], ["dog", "", "What a hog, to swallow a dog!"], ["cat", "", "Imagine that, to swallow a cat!"], ["bird", "", "How absurd to swallow a bird!"], ["spider", "that wriggled...", "It wriggled..."], ["fly", "", "I don't know why..."], ]
123. DATA = [ ["horse", "", "She's dead, of course!"], ["cow", "", "I don't know how..."], ["goat", "", "Just opened her throat..."], ["dog", "", "What a hog, to swallow a dog!"], ["cat", "", "Imagine that, to swallow a cat!"], ["bird", "", "How absurd to swallow a bird!"], ["spider", "that wriggled...", "It wriggled..."], ["fly", "", "I don't know why..."], ]
124. def critters @critters ||= DATA.map {|row| Critter.new(*row) } end
125. when 7 "I know an old lady who swallowed a %s.\n" % "cow" + "%s\n" % "I don't know how she swallowed..." + "She swallowed the %s to catch the %s.\n" % ["cow", "goat"] + "She swallowed the %s to catch the %s.\n" % ["goat", "dog"] + "She swallowed the %s to catch the %s.\n" % ["dog", "cat"] + "She swallowed the %s to catch the %s.\n" % ["cat", "bird"] + "She swallowed the %s to catch the %s.\n" % ["bird", "spider that..."] + "She swallowed the %s to catch the %s.\n" % ["spider", "fly"] + "%s\n" % "I don't know why she swallowed..."
126. when 7 "I know an old lady who swallowed a %s.\n" % critters.last(7).first.name + "%s\n" % "I don't know how she swallowed..." + "She swallowed the %s to catch the %s.\n" % ["cow", "goat"] + "She swallowed the %s to catch the %s.\n" % ["goat", "dog"] + "She swallowed the %s to catch the %s.\n" % ["dog", "cat"] + "She swallowed the %s to catch the %s.\n" % ["cat", "bird"] + "She swallowed the %s to catch the %s.\n" % ["bird", "spider that..."] + "She swallowed the %s to catch the %s.\n" % ["spider", "fly"] + "%s\n" % "I don't know why she swallowed..."
127. when 7 "I know an old lady who swallowed a %s.\n" % critters.last(7).first.name + "%s\n" % critters.last(7).first.aside + "She swallowed the %s to catch the %s.\n" % ["cow", "goat"] + "She swallowed the %s to catch the %s.\n" % ["goat", "dog"] + "She swallowed the %s to catch the %s.\n" % ["dog", "cat"] + "She swallowed the %s to catch the %s.\n" % ["cat", "bird"] + "She swallowed the %s to catch the %s.\n" % ["bird", "spider that..."] + "She swallowed the %s to catch the %s.\n" % ["spider", "fly"] + "%s\n" % "I don't know why she swallowed..."
128. when 7 "I know an old lady who swallowed a %s.\n" % critters.last(7).first.name + "%s\n" % critters.last(7).first.aside + "She swallowed the %s to catch the %s.\n" % chain(7) + "%s\n" % "I don't know why she swallowed..."
129. when 7 "I know an old lady who swallowed a %s.\n" % critters.last(7).first.name + "%s\n" % critters.last(7).first.aside + "She swallowed the %s to catch the %s.\n" % chain(7) + "%s\n" % critters.last.aside
130. 1. How to construct a verse. 2. How to string verses together. 3. Support for arbitrary creatures.
131. 1. How to construct a verse. 2. How to string verses together. 3. Support for arbitrary creatures.
132. 1. How to construct a verse. 2. How to string verses together. 3. Support for arbitrary creatures.
133. 1. How to construct a verse. 2. How to string verses together. 3. Support for arbitrary creatures. A. Hard-coded DATA constant.
134. 1. How to construct a verse. 2. How to string verses together. 3. Support for arbitrary creatures. A. Hard-coded DATA constant. B. Assumptions about creature count.
135. def critters @critters ||= DATA.map {|row| Critter.new(*row) } end
136. def critters @critters ||= DATA.map {|row| Critter.new(*row) } end
137. def critters @critters ||= DATA.map {|row| Critter.new(*row) } end def initialize(data = DATA) end
138. def critters @critters ||= DATA.map {|row| Critter.new(*row) } end def initialize(data = DATA) @data = data end
139. def critters @critters ||= DATA.map {|row| Critter.new(*row) } end attr_reader :data def initialize(data = DATA) @data = data end
140. def critters @critters ||= data.map {|row| Critter.new(*row) } end attr_reader :data def initialize(data = DATA) @data = data end
141. 1. How to construct a verse. 2. How to string verses together. 3. Support for arbitrary creatures. A. Hard-coded DATA constant. B. Assumptions about creature count.
142. Small steps.
143. Safe (adjective) Free from hurt, injury, danger, or risk.
144. Safe (adjective) An edit where the code works both before and after the change.
145. 1. How to construct a verse. 2. How to string verses together. 3. Support for arbitrary creatures. A. Hard-coded DATA constant. B. Assumptions about creature count.
146. def lyrics (1..8).map {|i| verse(i) }.join("\n") end
147. def lyrics (1..8).map {|i| verse(i) }.join("\n") end
148. def lyrics (1..critters.count).map {|i| verse(i) }.join("\n") end
149. case i when 1 # ... when 2 # ... when 3 # ... when 4 # ... when 5 # ... when 6 # ... when 7 # ... when 8 # ... end
150. # ... when 2 "I know an old lady who swallowed a %s.\n" % critters.last(3).first.name + "%s\n" % critters.last(3).first.aside + "%s\n" % chain(3) + "%s\n" % critters.last.aside when 3 "I know an old lady who swallowed a %s.\n" % critters.last(4).first.name + "%s\n" % critters.last(4).first.aside + "%s\n" % chain(4) + "%s\n" % critters.last.aside when 4 # ...
151. # ... when 2 "I know an old lady who swallowed a %s.\n" % critters.last(3).first.name + "%s\n" % critters.last(3).first.aside + "%s\n" % chain(3) + "%s\n" % critters.last.aside when 3 "I know an old lady who swallowed a %s.\n" % critters.last(4).first.name + "%s\n" % critters.last(4).first.aside + "%s\n" % chain(4) + "%s\n" % critters.last.aside when 4 # ...
152. # ... when 2 "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside + "%s\n" % chain(i) + "%s\n" % critters.last.aside when 3 "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside + "%s\n" % chain(i) + "%s\n" % critters.last.aside when 4 # ...
153. case i when 1 # ... when 2..7 "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside + "%s\n" % chain(i) + "%s\n" % critters.last.aside when 8 # ... end
154. case i when 1 "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside when 2..7 "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside + "%s\n" % chain(i) + "%s\n" % critters.last.aside when 8 "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside end
155. case i when 1, 8 "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside when 2..7 "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside + "%s\n" % chain(i) + "%s\n" % critters.last.aside end
156. case i when 1, 8 "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside when 2..7 "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside + "%s\n" % chain(i) + "%s\n" % critters.last.aside end
157. case i when 1, critters.count "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside when 2..7 "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside + "%s\n" % chain(i) + "%s\n" % critters.last.aside end
158. case i when 1, critters.count "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside else "I know an old lady who swallowed a %s.\n" % critters.last(i).first.name + "%s\n" % critters.last(i).first.aside + "%s\n" % chain(i) + "%s\n" % critters.last.aside end
159. 1. How to construct a verse. 2. How to string verses together. 3. Support for arbitrary creatures. A. Hard-coded DATA constant. B. Assumptions about creature count.
160. And now, new behavior!
161. data = [ ["D", "", "Nope."], ["C", "", "ZOMG C!"], ["B", "that bla bla", "Squee, B!"], ["A", "", "IDK why A."], ]
162. data = <<~SONG I know an old lady who swallowed an A. IDK why A. I know an old lady who swallowed a B. Squee, B! She swallowed the B to catch the A. IDK why A. I know an old lady who swallowed a C. ZOMG C! She swallowed the C to catch the B that bla bla. She swallowed the B to catch the A. IDK why A. I know an old lady who swallowed a D. Nope. SONG
163. data = <<~SONG I know an old lady who swallowed an A. IDK why A. I know an old lady who swallowed a B. Squee, B! She swallowed the B to catch the A. IDK why A. I know an old lady who swallowed a C. ZOMG C! She swallowed the C to catch the B that bla bla. She swallowed the B to catch the A. IDK why A. I know an old lady who swallowed a D. Nope. SONG
164. data = <<~SONG I know an old lady who swallowed an A. IDK why A. I know an old lady who swallowed a B. Squee, B! She swallowed the B to catch the A. IDK why A. I know an old lady who swallowed a C. ZOMG C! She swallowed the C to catch the B that bla bla. She swallowed the B to catch the A. IDK why A. I know an old lady who swallowed a D. Nope. SONG
165. data = <<~SONG I know an old lady who swallowed an A. IDK why A. I know an old lady who swallowed a B. Squee, B! She swallowed the B to catch the A. IDK why A. I know an old lady who swallowed a C. ZOMG C! She swallowed the C to catch the B that bla bla. She swallowed the B to catch the A. IDK why A. I know an old lady who swallowed a D. Nope. SONG
166. data = <<~SONG I know an old lady who swallowed an A. # ... Nope. SONG assert_equal expected, Song.new(data).lyrics
167. data = [ ["D", "", "Nope."], ["C", "", "ZOMG C!"], ["B", "that bla bla", "Squee, B!"], ["A", "", "IDK why A."], ]
168. data = [ ["a", "D", "", "Nope."], ["a", "C", "", "ZOMG C!"], ["a", "B", "that bla bla", "Squee, B!"], ["an", "A", "", "IDK why A."], ]
170. —Kent Beck Make the change easy then make the easy change.
171. (warning: this may be hard) —Kent Beck Make the change easy then make the easy change.
172. Take smaller steps.
173. Thank you.