Practical Debugging

People give ruby a bad reputation for speed, efficiency, weak typing, etc. But one of the biggest benefits of an interpreted language is the ability to debug and introspect quickly without compilation. Oftentimes developers reach for heavy-handed libraries to debug their application when they could just as easily get the information they need by using tools they already have.

In this talk you will learn practical techniques to make debugging easier. You will see how simple techniques from the ruby standard library can greatly increase your ability to keep your codebase clean and bug-free.

Transcript

1. Practical Debugging
2. ~/debugging $ bin/minesweeper ... board.rb:49:in `block (2 levels) in build_cells': undefined method `text' for nil:NilClass (NoMethodError) from ... board.rb:43:in `times' from ... board.rb:43:in `each' from ... board.rb:43:in `map' from ... board.rb:43:in `block in build_cells' from ... board.rb:42:in `times' from ... board.rb:42:in `each' from ... board.rb:42:in `flat_map' from ... board.rb:42:in `build_cells' from ... board.rb:17:in `start' from ... minesweeper.rb:8:in `start' from bin/minesweeper:7:in `<main>’ ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
3. Intro • Interface • State • Flow • Tradeoffs
4. Remain calm Intro • Interface • State • Flow • Tradeoffs
5. What would StackOverflow do? Intro • Interface • State • Flow • Tradeoffs
6. What would StackOverflow do? #WWSOD Intro • Interface • State • Flow • Tradeoffs
7. Use pry Use byebug Intro • Interface • State • Flow • Tradeoffs
8. Use pry Use byebug Intro • Interface • State • Flow • Tradeoffs
9. Use pry Use byebug Intro • Interface • State • Flow • Tradeoffs
10. Use pry Use byebug Intro • Interface • State • Flow • Tradeoffs
11. Use pry Use byebug Intro • Interface • State • Flow • Tradeoffs
12. Use pry Use the rub Intro • Interface • State • Flow • Tradeoffs
13. Use pry Use the ruby debugger Intro • Interface • State • Flow • Tradeoffs
14. Use pry Use the ruby debugger Intro • Interface • State • Flow • Tradeoffs
15. Use pry Use the ruby debugger Intro • Interface • State • Flow • Tradeoffs
16. Use pry Use the ruby debugger Intro • Interface • State • Flow • Tradeoffs
17. At the end of the day, people want bug-free code. They don’t care how it got that way. Intro • Interface • State • Flow • Tradeoffs
18. You don’t get style points in debugging. Intro • Interface • State • Flow • Tradeoffs
19. The ruby standard library has every tool you need to debug effectively. Intro • Interface • State • Flow • Tradeoffs
20. Debugging Intro • Interface • State • Flow • Tradeoffs
21. What kind of problem are you solving? Intro • Interface • State • Flow • Tradeoffs
22. Interface problem Intro • Interface • State • Flow • Tradeoffs
23. Interface problem State problem Intro • Interface • State • Flow • Tradeoffs
24. Interface problem State problem Flow problem Intro • Interface • State • Flow • Tradeoffs
25. Interface problems Intro • Interface • State • Flow • Tradeoffs
26. Interface problems occur when you don’t understand the dependent structure of methods or constants. Intro • Interface • State • Flow • Tradeoffs
27. Why is this thing nil? Intro • Interface • State • Flow • Tradeoffs
28. Why is this thing nil? Why can’t I call the method I want? Intro • Interface • State • Flow • Tradeoffs
29. Why is this thing nil? Why can’t I call the method I want? What are the constants I can reference? Intro • Interface • State • Flow • Tradeoffs
30. Why is this thing nil? Why can’t I call the method I want? What are the constants I can reference? What can this object see and do? Intro • Interface • State • Flow • Tradeoffs
31. Why is this thing nil? Why can’t I call the method I want? What are the constants I can reference? What can this object see and do? Oh god oh god what is this gem even doing? Intro • Interface • State • Flow • Tradeoffs
32. Why is this thing nil? Why can’t I call the method I want? What are the constants I can reference? What can this object see and do? Oh god oh god what is this gem even doing?
 I can’t even. Intro • Interface • State • Flow • Tradeoffs
33. Why is this thing nil? Intro • Interface • State • Flow • Tradeoffs
34. ~/debugging $ bin/minesweeper ... board.rb:57:in `[]': no implicit conversion from nil to integer (TypeError) from ... board.rb:57:in `block (3 levels) in build_cells' from ... board.rb:57:in `count' from ... board.rb:57:in `block (2 levels) in build_cells' from ... board.rb:44:in `times' from ... board.rb:44:in `each' from ... board.rb:44:in `map' from ... board.rb:44:in `block in build_cells' from ... board.rb:43:in `times' from ... board.rb:43:in `each' from ... board.rb:43:in `flat_map' from ... board.rb:43:in `build_cells' from ... board.rb:17:in `start' from ... minesweeper.rb:9:in `start' from bin/minesweeper:7:in `<main>' Intro • Interface • State • Flow • Tradeoffs
35. ~/debugging $ bin/minesweeper ... board.rb:57:in `[]': no implicit conversion from nil to integer (TypeError) from ... board.rb:57:in `block (3 levels) in build_cells' from ... board.rb:57:in `count' from ... board.rb:57:in `block (2 levels) in build_cells' from ... board.rb:44:in `times' from ... board.rb:44:in `each' from ... board.rb:44:in `map' from ... board.rb:44:in `block in build_cells' from ... board.rb:43:in `times' from ... board.rb:43:in `each' from ... board.rb:43:in `flat_map' from ... board.rb:43:in `build_cells' from ... board.rb:17:in `start' from ... minesweeper.rb:9:in `start' from bin/minesweeper:7:in `<main>' Intro • Interface • State • Flow • Tradeoffs
36. module MineSweeper class Board def build_cells(tk_root) ... neighbors = neighbors_for(ycoord, xcoord) mine_count = neighbors.count { |neighbor| mines[neighbor] } ... end def neighbors_for(ycoord, xcoord) [ index_for(ycoord - 1, xcoord - 1), index_for(ycoord - 1, xcoord), ... ] end def index_for(ycoord, xcoord) return nil if ycoord < 0 || xcoord < 0 || ycoord >= height || xcoord >= width ycoord * width + xcoord end end end Intro • Interface • State • Flow • Tradeoffs
37. module MineSweeper class Board def build_cells(tk_root) ... neighbors = neighbors_for(ycoord, xcoord) mine_count = neighbors.count { |neighbor| mines[neighbor] } ... end def neighbors_for(ycoord, xcoord) [ index_for(ycoord - 1, xcoord - 1), index_for(ycoord - 1, xcoord), ... ] end def index_for(ycoord, xcoord) return nil if ycoord < 0 || xcoord < 0 || ycoord >= height || xcoord >= width ycoord * width + xcoord end end end Intro • Interface • State • Flow • Tradeoffs
38. module MineSweeper class Board def build_cells(tk_root) ... neighbors = neighbors_for(ycoord, xcoord) mine_count = neighbors.count { |neighbor| mines[neighbor] } ... end def neighbors_for(ycoord, xcoord) [ index_for(ycoord - 1, xcoord - 1), index_for(ycoord - 1, xcoord), ... ] end def index_for(ycoord, xcoord) return nil if ycoord < 0 || xcoord < 0 || ycoord >= height || xcoord >= width ycoord * width + xcoord end end end Intro • Interface • State • Flow • Tradeoffs
39. module MineSweeper class Board def build_cells(tk_root) ... neighbors = neighbors_for(ycoord, xcoord) mine_count = neighbors.count { |neighbor| mines[neighbor] } ... end def neighbors_for(ycoord, xcoord) [ index_for(ycoord - 1, xcoord - 1), index_for(ycoord - 1, xcoord), ... ] end def index_for(ycoord, xcoord) return nil if ycoord < 0 || xcoord < 0 || ycoord >= height || xcoord >= width ycoord * width + xcoord end end end Intro • Interface • State • Flow • Tradeoffs
40. module MineSweeper class Board def build_cells(tk_root) ... neighbors = neighbors_for(ycoord, xcoord) mine_count = neighbors.count { |neighbor| mines[neighbor] } ... end def neighbors_for(ycoord, xcoord) [ index_for(ycoord - 1, xcoord - 1), index_for(ycoord - 1, xcoord), ... ] end def index_for(ycoord, xcoord) return nil if ycoord < 0 || xcoord < 0 || ycoord >= height || xcoord >= width ycoord * width + xcoord end end end Intro • Interface • State • Flow • Tradeoffs
41. module MineSweeper class Board def build_cells(tk_root) ... neighbors = neighbors_for(ycoord, xcoord) mine_count = neighbors.count { |neighbor| mines[neighbor] } ... end def neighbors_for(ycoord, xcoord) [ index_for(ycoord - 1, xcoord - 1), index_for(ycoord - 1, xcoord), ... ] end def index_for(ycoord, xcoord) return nil if ycoord < 0 || xcoord < 0 || ycoord >= height || xcoord >= width ycoord * width + xcoord end end end Intro • Interface • State • Flow • Tradeoffs
42. module MineSweeper class Board def build_cells(tk_root) ... neighbors = neighbors_for(ycoord, xcoord) mine_count = neighbors.count { |neighbor| mines[neighbor] } ... end def neighbors_for(ycoord, xcoord) [ index_for(ycoord - 1, xcoord - 1), index_for(ycoord - 1, xcoord), ... ] end Option[Int] index_for(ycoord, xcoord) return nil if ycoord < 0 || xcoord < 0 || ycoord >= height || xcoord >= width ycoord * width + xcoord end end end Intro • Interface • State • Flow • Tradeoffs
43. module MineSweeper class Board def build_cells(tk_root) ... neighbors = neighbors_for(ycoord, xcoord) mine_count = neighbors.count { |neighbor| mines[neighbor] } ... end def neighbors_for(ycoord, xcoord) [ index_for(ycoord - 1, xcoord - 1), index_for(ycoord - 1, xcoord), ... ] end Optional<Integer> index_for(ycoord, xcoord) return nil if ycoord < 0 || xcoord < 0 || ycoord >= height || xcoord >= width ycoord * width + xcoord end end end Intro • Interface • State • Flow • Tradeoffs
44. module MineSweeper class Board def build_cells(tk_root) ... neighbors = neighbors_for(ycoord, xcoord) mine_count = neighbors.count { |neighbor| mines[neighbor] } ... end def neighbors_for(ycoord, xcoord) [ index_for(ycoord - 1, xcoord - 1), index_for(ycoord - 1, xcoord), ... ] end Maybe Int index_for(ycoord, xcoord) return nil if ycoord < 0 || xcoord < 0 || ycoord >= height || xcoord >= width ycoord * width + xcoord end end end Intro • Interface • State • Flow • Tradeoffs
45. module MineSweeper class Board def build_cells(tk_root) ... neighbors = neighbors_for(ycoord, xcoord) mine_count = neighbors.count { |neighbor| mines[neighbor] } ... end def neighbors_for(ycoord, xcoord) [ index_for(ycoord - 1, xcoord - 1), index_for(ycoord - 1, xcoord), ... ] end def index_for(ycoord, xcoord) return nil if ycoord < 0 || xcoord < 0 || ycoord >= height || xcoord >= width ycoord * width + xcoord end end end Intro • Interface • State • Flow • Tradeoffs
46. module MineSweeper class Board def build_cells(tk_root) ... neighbors = neighbors_for(ycoord, xcoord) mine_count = neighbors.count { |neighbor| mines[neighbor] } ... end def neighbors_for(ycoord, xcoord) [ index_for(ycoord - 1, xcoord - 1), index_for(ycoord - 1, xcoord), ... ].compact end def index_for(ycoord, xcoord) return nil if ycoord < 0 || xcoord < 0 || ycoord >= height || xcoord >= width ycoord * width + xcoord end end end Intro • Interface • State • Flow • Tradeoffs
47. Why can’t I call the method I want? Intro • Interface • State • Flow • Tradeoffs
48. ~/debugging $ bin/minesweeper ... tk-0.1.2/lib/tk.rb:4984:in `rescue in method_missing': unknown option 'mines' for #<Tk::Label:0x007fb839800658 @path=".w00200"> (deleted widget?) (NameError) from ... tk-0.1.2/lib/tk.rb:4980:in `method_missing' from ... minesweeper/board.rb:63:in `block in build_status_label' from ... minesweeper/board.rb:62:in `new' from ... minesweeper/board.rb:62:in `build_status_label' from ... minesweeper/board.rb:18:in `start' from ... minesweeper.rb:8:in `start' from bin/minesweeper:7:in `<main>’ ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
49. ~/debugging $ bin/minesweeper ... tk-0.1.2/lib/tk.rb:4984:in `rescue in method_missing': unknown option 'mines' for #<Tk::Label:0x007fb839800658 @path=".w00200"> (deleted widget?) (NameError) from ... tk-0.1.2/lib/tk.rb:4980:in `method_missing' from ... minesweeper/board.rb:63:in `block in build_status_label' from ... minesweeper/board.rb:62:in `new' from ... minesweeper/board.rb:62:in `build_status_label' from ... minesweeper/board.rb:18:in `start' from ... minesweeper.rb:8:in `start' from bin/minesweeper:7:in `<main>’ ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
50. ~/debugging $ bin/minesweeper ... tk-0.1.2/lib/tk.rb:4984:in `rescue in method_missing': unknown option 'mines' for #<Tk::Label:0x007fb839800658 @path=".w00200"> (deleted widget?) (NameError) from ... tk-0.1.2/lib/tk.rb:4980:in `method_missing' from ... minesweeper/board.rb:63:in `block in build_status_label' from ... minesweeper/board.rb:62:in `new' from ... minesweeper/board.rb:62:in `build_status_label' from ... minesweeper/board.rb:18:in `start' from ... minesweeper.rb:8:in `start' from bin/minesweeper:7:in `<main>’ ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
51. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) TkLabel.new(tk_root) do text "#{mines} mines left" grid(column: 0, row: 0, columnspan: width) end end end end Intro • Interface • State • Flow • Tradeoffs
52. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) TkLabel.new(tk_root) do text "#{mines} mines left" grid(column: 0, row: 0, columnspan: width) end end end end Intro • Interface • State • Flow • Tradeoffs
53. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) TkLabel.new(tk_root) do p methods.grep(/mines/) p methods exit text "#{mines} mines left" grid(column: 0, row: 0, columnspan: width) end end end end Intro • Interface • State • Flow • Tradeoffs
54. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) TkLabel.new(tk_root) do p methods.grep(/mines/) p methods exit text "#{mines} mines left" grid(column: 0, row: 0, columnspan: width) end end end end Intro • Interface • State • Flow • Tradeoffs
55. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) TkLabel.new(tk_root) do p methods.grep(/mines/) p methods exit text "#{mines} mines left" grid(column: 0, row: 0, columnspan: width) end end end end Intro • Interface • State • Flow • Tradeoffs
56. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) TkLabel.new(tk_root) do p methods.grep(/mines/) puts methods.inspect exit text "#{mines} mines left" grid(column: 0, row: 0, columnspan: width) end end end end Intro • Interface • State • Flow • Tradeoffs
57. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) TkLabel.new(tk_root) do p methods.grep(/mines/) p methods exit text "#{mines} mines left" grid(column: 0, row: 0, columnspan: width) end end end end Intro • Interface • State • Flow • Tradeoffs
58. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) TkLabel.new(tk_root) do p methods.grep(/mines/) p methods exit text "#{mines} mines left" grid(column: 0, row: 0, columnspan: width) end end end end Intro • Interface • State • Flow • Tradeoffs
59. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) TkLabel.new(tk_root) do p methods.grep(/mines/) p methods exit text "#{mines} mines left" grid(column: 0, row: 0, columnspan: width) end end end end Intro • Interface • State • Flow • Tradeoffs
60. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) TkLabel.new(tk_root) do p methods.grep(/mines/) p methods exit text "#{mines} mines left" grid(column: 0, row: 0, columnspan: width) end end end end Intro • Interface • State • Flow • Tradeoffs
61. ~/debugging $ bin/minesweeper [] [:raise, :exist?, :subcommand, :bind_class, :database _classname, :database_class, :pack_in, :pack, :unpack , :pack_configure, :pack_config, :pack_propagate, :pa ck_info, :pack_slaves, :grid_in, :grid_anchor, :grid_ bbox, :grid_config, :grid_configure, :grid_columnconf ig, :grid_columnconfigure, :grid_rowconfig, :grid_row configure, :grid_columnconfiginfo, :grid_rowconfiginf o, :grid_column, :grid_row, :grid_info, :grid_locatio n, :thread_wait, :grid_propagate, :pack_forget, :grid _remove, :grid, :grid_slaves, :grid_forget, :ungrid, :place, :grid_size, :place_forget, :unplace, :place_c onfig, :place_configure, :set_focus, :place_in, :lowe r_window, :current_grab, :raise_window, ... ] ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
62. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) TkLabel.new(tk_root) do p methods.grep(/mines/) p methods exit text "#{mines} mines left" grid(column: 0, row: 0, columnspan: width) end end end end Intro • Interface • State • Flow • Tradeoffs
63. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) TkLabel.new(tk_root) do text "#{mines} mines left" grid(column: 0, row: 0, columnspan: width) end end end end Intro • Interface • State • Flow • Tradeoffs
64. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) initial_status = "#{mines} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(column: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
65. What are the constants I can reference? Intro • Interface • State • Flow • Tradeoffs
66. module MineSweeper module Cell class Base end end class Cell::Mine < Base end class Cell::Neighbor < Base end class Cell::Empty < Base end end Intro • Interface • State • Flow • Tradeoffs
67. ~/debugging $ ruby examples/module_nesting_1.rb examples/module_nesting_1.rb:7:in `<module:MineSweeper>': uninitialized constant MineSweeper::Base (NameError) from examples/module_nesting_1.rb:1:in `<main>' ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
68. ~/debugging $ ruby examples/module_nesting_1.rb examples/module_nesting_1.rb:7:in `<module:MineSweeper>': uninitialized constant MineSweeper::Base (NameError) from examples/module_nesting_1.rb:1:in `<main>' ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
69. module MineSweeper module Cell class Base end end class Cell::Mine < Base end class Cell::Neighbor < Base end class Cell::Empty < Base end end Intro • Interface • State • Flow • Tradeoffs
70. module MineSweeper module Cell class Base end end puts Module.nesting; exit class Cell::Mine < Base end class Cell::Neighbor < Base end class Cell::Empty < Base end end Intro • Interface • State • Flow • Tradeoffs
71. ~/debugging $ ruby examples/module_nesting_1.rb MineSweeper ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
72. module MineSweeper module Cell class Base end end puts Module.nesting; exit class Cell::Mine < Base end class Cell::Neighbor < Base end class Cell::Empty < Base end end Intro • Interface • State • Flow • Tradeoffs
73. module MineSweeper module Cell class Base end puts Module.nesting; exit class Mine < Base end class Neighbor < Base end class Empty < Base end end end Intro • Interface • State • Flow • Tradeoffs
74. module MineSweeper module Cell class Base end puts Module.nesting; exit class Mine < Base end class Neighbor < Base end class Empty < Base end end end Intro • Interface • State • Flow • Tradeoffs
75. ~/debugging $ ruby examples/module_nesting_2.rb MineSweeper::Cell MineSweeper ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
76. What can this object see and do? Intro • Interface • State • Flow • Tradeoffs
77. def puts_constants(constant) puts constant.name constant.constants.each do |identifier| child_constant = constant.const_get(identifier) if child_constant != constant && child_constant.is_a?(Class) puts_constants(child_constant) end end end puts_constants(MineSweeper) Intro • Interface • State • Flow • Tradeoffs
78. def puts_constants(constant) puts constant.name constant.constants.each do |identifier| child_constant = constant.const_get(identifier) if child_constant != constant && child_constant.is_a?(Class) puts_constants(child_constant) end end end puts_constants(MineSweeper) Intro • Interface • State • Flow • Tradeoffs
79. def puts_constants(constant) puts constant.name constant.constants.each do |identifier| child_constant = constant.const_get(identifier) if child_constant != constant && child_constant.is_a?(Class) puts_constants(child_constant) end end end puts_constants(MineSweeper) Intro • Interface • State • Flow • Tradeoffs
80. def puts_constants(constant) puts constant.name constant.constants.each do |identifier| child_constant = constant.const_get(identifier) if child_constant != constant && child_constant.is_a?(Class) puts_constants(child_constant) end end end puts_constants(MineSweeper) Intro • Interface • State • Flow • Tradeoffs
81. def puts_constants(constant) puts constant.name constant.constants.each do |identifier| child_constant = constant.const_get(identifier) if child_constant != constant && child_constant.is_a?(Class) puts_constants(child_constant) end end end puts_constants(MineSweeper) Intro • Interface • State • Flow • Tradeoffs
82. ~/debugging $ ruby -Ilib -rminesweeper examples/constants.rb MineSweeper MineSweeper::Board MineSweeper::Cell ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
83. def puts_constants(constant) puts constant.name constant.constants.each do |identifier| child_constant = constant.const_get(identifier) if child_constant != constant && child_constant.is_a?(Class) puts_constants(child_constant) end end end puts_constants(MineSweeper) Intro • Interface • State • Flow • Tradeoffs
84. def puts_constants(constant) puts constant.name constant.constants.each do |identifier| child_constant = constant.const_get(identifier) if child_constant != constant && child_constant.is_a?(Class) puts_constants(child_constant) end end end puts_constants(ActiveRecord) Intro • Interface • State • Flow • Tradeoffs
85. ~/debugging $ ruby -Iactiverecord -ractive_record examples/constants.rb ActiveRecord ActiveRecord::LazyAttributeHash ActiveRecord::StatementInvalid ActiveRecord::MigrationProxy Process::Tms ActiveRecord::Attribute ActiveRecord::Base ActiveRecord::Store::StringKeyedHashAccessor ActiveRecord::Store::IndifferentHashAccessor ActiveRecord::Store::IndifferentCoder ActiveRecord::Store::HashAccessor ActiveRecord::Reflection::ThroughReflection ... ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
86. ~/debugging $ ruby -Ilib -rminesweeper -e \ > "p MineSweeper::Board.instance_methods" [:status, :start, :width, :height, :mines, :cells, :click, :update_status, :instance_of?, :kind_of?, :is_a?, :tap, :p ublic_send, :remove_instance_variable, :public_method, :si ngleton_method, :instance_variable_set, :define_singleton_ method, :method, :extend, :to_enum, :enum_for, :<=>, :===, :=~, :! ~, :eql?, :respond_to?, :freeze, :inspect, :object_id, :se nd, :display, :to_s, :nil?, :hash, :class, :singleton_clas s, :clone, :dup, :itself, :taint, :tainted?, :untaint, :un trust, :untrusted?, :trust, :frozen?, :methods, :singleton _methods, :protected_methods, :private_methods, ...] ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
87. ~/debugging $ ruby -Ilib -rminesweeper -e \ > "p MineSweeper::Board.instance_methods" [:status, :start, :width, :height, :mines, :cells, :click, :update_status, :instance_of?, :kind_of?, :is_a?, :tap, :p ublic_send, :remove_instance_variable, :public_method, :si ngleton_method, :instance_variable_set, :define_singleton_ method, :method, :extend, :to_enum, :enum_for, :<=>, :===, :=~, :! ~, :eql?, :respond_to?, :freeze, :inspect, :object_id, :se nd, :display, :to_s, :nil?, :hash, :class, :singleton_clas s, :clone, :dup, :itself, :taint, :tainted?, :untaint, :un trust, :untrusted?, :trust, :frozen?, :methods, :singleton _methods, :protected_methods, :private_methods, ...] ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
88. ~/debugging $ ruby -Ilib -rminesweeper -e \ > "p MineSweeper::Board.instance_methods" [:status, :start, :width, :height, :mines, :cells, :click, :update_status, :instance_of?, :kind_of?, :is_a?, :tap, :p ublic_send, :remove_instance_variable, :public_method, :si ngleton_method, :instance_variable_set, :define_singleton_ method, :method, :extend, :to_enum, :enum_for, :<=>, :===, :=~, :! ~, :eql?, :respond_to?, :freeze, :inspect, :object_id, :se nd, :display, :to_s, :nil?, :hash, :class, :singleton_clas s, :clone, :dup, :itself, :taint, :tainted?, :untaint, :un trust, :untrusted?, :trust, :frozen?, :methods, :singleton _methods, :protected_methods, :private_methods, ...] ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
89. ~/debugging $ ruby -Ilib -rminesweeper -e \ > "p MineSweeper::Board.instance_methods" [:status, :start, :width, :height, :mines, :cells, :click, :update_status, :instance_of?, :kind_of?, :is_a?, :tap, :p ublic_send, :remove_instance_variable, :public_method, :si ngleton_method, :instance_variable_set, :define_singleton_ method, :method, :extend, :to_enum, :enum_for, :<=>, :===, :=~, :! ~, :eql?, :respond_to?, :freeze, :inspect, :object_id, :se nd, :display, :to_s, :nil?, :hash, :class, :singleton_clas s, :clone, :dup, :itself, :taint, :tainted?, :untaint, :un trust, :untrusted?, :trust, :frozen?, :methods, :singleton _methods, :protected_methods, :private_methods, ...] ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
90. ~/debugging $ ruby -Ilib -rminesweeper -e \ > "p MineSweeper::Board.instance_methods(false)" [:status, :start, :width, :height, :mines, :cells, :click, :update_status] ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
91. ~/debugging $ ruby -Ilib -rminesweeper -e \ > "p MineSweeper::Board.private_instance_methods" [:initialize, :build_cells, :build_status_label, :index_fo r, :neighbors_for, :DelegateClass, :TkPack, :TkGrid, :TkPl ace, :sprintf, :format, :Integer, :Float, :String, :Array, :Hash, :fail, :iterator?, :__method__, :catch, :__dir__, : loop, :global_variables, :throw, :block_given?, :raise, :_ _callee__, :eval, :Rational, :trace_var, :untrace_var, :Co mplex, :at_exit, :set_trace_func, :gem, :select, :caller, :caller_locations, :`, :test, :fork, :exit, :sleep, :respo nd_to_missing?, :gem_original_require, :load, :exec, :exit !, :system, :spawn, :abort, :syscall, :open, :printf, :pri nt, :putc, :puts, :gets, :readlines, :readline, ...] ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
92. ~/debugging $ ruby -Ilib -rminesweeper -e \ > "p MineSweeper::Board.private_instance_methods(false)" [:initialize, :build_cells, :build_status_label, :index_fo r, :neighbors_for] ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
93. Oh god oh god what is this gem even doing? Intro • Interface • State • Flow • Tradeoffs
94. ~/debugging $ bin/minesweeper ... tk-0.1.2/lib/tk.rb:2054:in `_invoke': ambiguous option "-colum": must be -column, -columnspan, -in, -ipadx, - ipady, -padx, -pady, -row, -rowspan, or -sticky (RuntimeError) from ... tk-0.1.2/lib/tk.rb:2054:in `_ip_invoke_core' from ... tk-0.1.2/lib/tk.rb:2090:in `_tk_call_core' from ... tk-0.1.2/lib/tk.rb:2118:in `tk_call_without_enc' from ... tk-0.1.2/lib/tk/grid.rb:97:in `configure' from ... tk-0.1.2/lib/tk.rb:5301:in `grid' from ... minesweeper/board.rb:67:in `block in build_status_label' from ... minesweeper/board.rb:65:in `new' from ... minesweeper/board.rb:65:in `build_status_label' from ... minesweeper/board.rb:18:in `start' from ... minesweeper.rb:7:in `start' from bin/minesweeper:7:in `<main>' Intro • Interface • State • Flow • Tradeoffs
95. ~/debugging $ bin/minesweeper ... tk-0.1.2/lib/tk.rb:2054:in `_invoke': ambiguous option "-colum": must be -column, -columnspan, -in, -ipadx, - ipady, -padx, -pady, -row, -rowspan, or -sticky (RuntimeError) from ... tk-0.1.2/lib/tk.rb:2054:in `_ip_invoke_core' from ... tk-0.1.2/lib/tk.rb:2090:in `_tk_call_core' from ... tk-0.1.2/lib/tk.rb:2118:in `tk_call_without_enc' from ... tk-0.1.2/lib/tk/grid.rb:97:in `configure' from ... tk-0.1.2/lib/tk.rb:5301:in `grid' from ... minesweeper/board.rb:67:in `block in build_status_label' from ... minesweeper/board.rb:65:in `new' from ... minesweeper/board.rb:65:in `build_status_label' from ... minesweeper/board.rb:18:in `start' from ... minesweeper.rb:7:in `start' from bin/minesweeper:7:in `<main>' Intro • Interface • State • Flow • Tradeoffs
96. ~/debugging $ bin/minesweeper ... tk-0.1.2/lib/tk.rb:2054:in `_invoke': ambiguous option "-colum": must be -column, -columnspan, -in, -ipadx, - ipady, -padx, -pady, -row, -rowspan, or -sticky (RuntimeError) from ... tk-0.1.2/lib/tk.rb:2054:in `_ip_invoke_core' from ... tk-0.1.2/lib/tk.rb:2090:in `_tk_call_core' from ... tk-0.1.2/lib/tk.rb:2118:in `tk_call_without_enc' from ... tk-0.1.2/lib/tk/grid.rb:97:in `configure' from ... tk-0.1.2/lib/tk.rb:5301:in `grid' from ... minesweeper/board.rb:67:in `block in build_status_label' from ... minesweeper/board.rb:65:in `new' from ... minesweeper/board.rb:65:in `build_status_label' from ... minesweeper/board.rb:18:in `start' from ... minesweeper.rb:7:in `start' from bin/minesweeper:7:in `<main>' Intro • Interface • State • Flow • Tradeoffs
97. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) initial_status = "#{mines} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(colum: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
98. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) initial_status = "#{mines} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(colum: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
99. ~/debugging $ bin/console irb(main):001:0> Intro • Interface • State • Flow • Tradeoffs
100. ~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(:grid) => #<UnboundMethod: Tk::Label(TkWindow)#grid> irb(main):002:0> Intro • Interface • State • Flow • Tradeoffs
101. ~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(:grid) => #<UnboundMethod: Tk::Label(TkWindow)#grid> irb(main):002:0> method.source_location => ["... ruby/gems/2.4.0/gems/tk-0.1.2/lib/tk.rb", 5298] irb(main):003:0> Intro • Interface • State • Flow • Tradeoffs
102. ~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(:grid) => #<UnboundMethod: Tk::Label(TkWindow)#grid> irb(main):002:0> method.source_location => ["... ruby/gems/2.4.0/gems/tk-0.1.2/lib/tk.rb", 5298] irb(main):003:0> Intro • Interface • State • Flow • Tradeoffs
103. ~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(:grid) => #<UnboundMethod: Tk::Label(TkWindow)#grid> irb(main):002:0> method.source_location => ["... ruby/gems/2.4.0/gems/tk-0.1.2/lib/tk.rb", 5298] irb(main):003:0> Intro • Interface • State • Flow • Tradeoffs
104. ~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(:grid) => #<UnboundMethod: Tk::Label(TkWindow)#grid> irb(main):002:0> method.source_location => ["... ruby/gems/2.4.0/gems/tk-0.1.2/lib/tk.rb", 5298] irb(main):003:0> Intro • Interface • State • Flow • Tradeoffs
105. class TkWindow<TkObject ... def grid(keys = nil) #tk_call 'grid', epath, *hash_kv(keys) if keys TkGrid.configure(self, keys) else TkGrid.configure(self) end self end end Intro • Interface • State • Flow • Tradeoffs
106. class TkWindow<TkObject ... def grid(keys = nil) #tk_call 'grid', epath, *hash_kv(keys) if keys TkGrid.configure(self, keys) else TkGrid.configure(self) end self end end Intro • Interface • State • Flow • Tradeoffs
107. ~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(:grid) => #<UnboundMethod: Tk::Label(TkWindow)#grid> irb(main):002:0> method.source_location => ["... gems/2.4.0/gems/tk-0.1.2/lib/tk.rb", 5298] irb(main):003:0> Intro • Interface • State • Flow • Tradeoffs
108. ~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(:grid) => #<UnboundMethod: Tk::Label(TkWindow)#grid> irb(main):002:0> method.source_location => ["... gems/2.4.0/gems/tk-0.1.2/lib/tk.rb", 5298] irb(main):003:0> method = TkGrid.method(:configure) => #<Method: TkGrid.configure> irb(main):004:0> Intro • Interface • State • Flow • Tradeoffs
109. ~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(:grid) => #<UnboundMethod: Tk::Label(TkWindow)#grid> irb(main):002:0> method.source_location => ["... gems/2.4.0/gems/tk-0.1.2/lib/tk.rb", 5298] irb(main):003:0> method = TkGrid.method(:configure) => #<Method: TkGrid.configure> irb(main):004:0> method.source_location => ["... gems/2.4.0/gems/tk-0.1.2/lib/tk/grid.rb", 59] irb(main):005:0> Intro • Interface • State • Flow • Tradeoffs
110. ~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(:grid) => #<UnboundMethod: Tk::Label(TkWindow)#grid> irb(main):002:0> method.source_location => ["... gems/2.4.0/gems/tk-0.1.2/lib/tk.rb", 5298] irb(main):003:0> method = TkGrid.method(:configure) => #<Method: TkGrid.configure> irb(main):004:0> method.source_location => ["... gems/2.4.0/gems/tk-0.1.2/lib/tk/grid.rb", 59] irb(main):005:0> Intro • Interface • State • Flow • Tradeoffs
111. module TkGrid ... def configure(*args) ... opts.each{|k, v| params.push("-#{k}") params.push(_epath(v)) # have to use 'epath' (hash_kv() is unavailable) } if Tk::TCL_MAJOR_VERSION < 8 || (Tk::TCL_MAJOR_VERSION == 8 && Tk::TCL_MINOR_VERSION <= 3) if params[0] == '-' || params[0] == 'x' || params[0] == '^' tk_call_without_enc('grid', *params) else tk_call_without_enc('grid', 'configure', *params) end else tk_call_without_enc('grid', 'configure', *params) end end end Intro • Interface • State • Flow • Tradeoffs
112. module TkGrid ... def configure(*args) ... opts.each{|k, v| params.push("-#{k}") params.push(_epath(v)) # have to use 'epath' (hash_kv() is unavailable) } if Tk::TCL_MAJOR_VERSION < 8 || (Tk::TCL_MAJOR_VERSION == 8 && Tk::TCL_MINOR_VERSION <= 3) if params[0] == '-' || params[0] == 'x' || params[0] == '^' tk_call_without_enc('grid', *params) else tk_call_without_enc('grid', 'configure', *params) end else tk_call_without_enc('grid', 'configure', *params) end end end Intro • Interface • State • Flow • Tradeoffs
113. module TkGrid ... def configure(*args) ... opts.each{|k, v| params.push("-#{k}") params.push(_epath(v)) # have to use 'epath' (hash_kv() is unavailable) } if Tk::TCL_MAJOR_VERSION < 8 || (Tk::TCL_MAJOR_VERSION == 8 && Tk::TCL_MINOR_VERSION <= 3) if params[0] == '-' || params[0] == 'x' || params[0] == '^' tk_call_without_enc('grid', *params) else tk_call_without_enc('grid', 'configure', *params) end else tk_call_without_enc('grid', 'configure', *params) end end end Intro • Interface • State • Flow • Tradeoffs
114. module TkGrid ... def configure(*args) ... opts.each{|k, v| params.push("-#{k}") params.push(_epath(v)) # have to use 'epath' (hash_kv() is unavailable) } p params if Tk::TCL_MAJOR_VERSION < 8 || (Tk::TCL_MAJOR_VERSION == 8 && Tk::TCL_MINOR_VERSION <= 3) if params[0] == '-' || params[0] == 'x' || params[0] == '^' tk_call_without_enc('grid', *params) else tk_call_without_enc('grid', 'configure', *params) end else tk_call_without_enc('grid', 'configure', *params) end end end Intro • Interface • State • Flow • Tradeoffs
115. ~/debugging $ bin/minesweeper [".w00000", "-column", 0, "-row", 1] [".w00001", "-column", 1, "-row", 1] ... [".w00197", "-column", 17, "-row", 10] [".w00198", "-column", 18, "-row", 10] [".w00199", "-column", 19, "-row", 10] [".w00200", "-colum", 0, "-row", 0, "-columnspan", 20] ... tk-0.1.2/lib/tk.rb:2054:in `_invoke': ambiguous option "-colum": must be -column, -columnspan, -in, - ipadx, -ipady, -padx, -pady, -row, -rowspan, or -sticky (RuntimeError) ... ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
116. ~/debugging $ bin/minesweeper [".w00000", "-column", 0, "-row", 1] [".w00001", "-column", 1, "-row", 1] ... [".w00197", "-column", 17, "-row", 10] [".w00198", "-column", 18, "-row", 10] [".w00199", "-column", 19, "-row", 10] [".w00200", "-colum", 0, "-row", 0, "-columnspan", 20] ... tk-0.1.2/lib/tk.rb:2054:in `_invoke': ambiguous option "-colum": must be -column, -columnspan, -in, - ipadx, -ipady, -padx, -pady, -row, -rowspan, or -sticky (RuntimeError) ... ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
117. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) initial_status = "#{mines} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(colum: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
118. module MineSweeper class Board attr_reader :width, :mines ... private ... def build_status_label(tk_root) initial_status = "#{mines} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(column: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
119. ~/debugging $ bundle exec gem pristine tk Restoring gems to pristine condition... Restored tk-0.1.2 ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
120. Lessons learned Intro • Interface • State • Flow • Tradeoffs
121. Account for every return type Intro • Interface • State • Flow • Tradeoffs
122. Account for constant and method lookup Intro • Interface • State • Flow • Tradeoffs
123. Take advantage of constant and method introspection Intro • Interface • State • Flow • Tradeoffs
124. Take advantage of the fact that gems aren't bytecode Intro • Interface • State • Flow • Tradeoffs
125. State problems Intro • Interface • State • Flow • Tradeoffs
126. State problems occur when the assumptions you made about the current state of the program are incorrect. Intro • Interface • State • Flow • Tradeoffs
127. How does this value change at this point? Intro • Interface • State • Flow • Tradeoffs
128. How does this value change at this point? What has been initialized at this point? Intro • Interface • State • Flow • Tradeoffs
129. How does this value change at this point? What has been initialized at this point? How many objects are allocated in this method? Intro • Interface • State • Flow • Tradeoffs
130. How does this value change at this point? Intro • Interface • State • Flow • Tradeoffs
131. module MineSweeper class Cell attr_reader :button ... private ... def update(board) button.text = display(board).to_s board.update_status end end end Intro • Interface • State • Flow • Tradeoffs
132. module MineSweeper class Cell attr_reader :button ... private ... def update(board) button.text = display(board).to_s board.update_status end end end Intro • Interface • State • Flow • Tradeoffs
133. module MineSweeper class Cell attr_reader :button ... private ... def update(board) ivars = instance_variables.map do |ivar| [ivar, instance_variable_get(ivar)] end puts "STATE=#{ivars.to_h.inspect}" puts "CURRENT=#{button.text} | NEW=#{display(board).to_s}" button.text = display(board).to_s board.update_status end end end Intro • Interface • State • Flow • Tradeoffs
134. module MineSweeper class Cell attr_reader :button ... private ... def update(board) ivars = instance_variables.map do |ivar| [ivar, instance_variable_get(ivar)] end puts "STATE=#{ivars.to_h.inspect}" puts "CURRENT=#{button.text} | NEW=#{display(board).to_s}" button.text = display(board).to_s board.update_status end end end Intro • Interface • State • Flow • Tradeoffs
135. module MineSweeper class Cell attr_reader :button ... private ... def update(board) ivars = instance_variables.map do |ivar| [ivar, instance_variable_get(ivar)] end puts "STATE=#{ivars.to_h.inspect}" puts "CURRENT=#{button.text} | NEW=#{display(board).to_s}" button.text = display(board).to_s board.update_status end end end Intro • Interface • State • Flow • Tradeoffs
136. module MineSweeper class Cell attr_reader :button ... private ... def update(board) ivars = instance_variables.map do |ivar| [ivar, instance_variable_get(ivar)] end puts "STATE=#{ivars.to_h.inspect}" puts "CURRENT=#{button.text} | NEW=#{display(board).to_s}" button.text = display(board).to_s board.update_status end end end Intro • Interface • State • Flow • Tradeoffs
137. module MineSweeper class Cell attr_reader :button ... private ... def update(board) ivars = instance_variables.map do |ivar| [ivar, instance_variable_get(ivar)] end puts "STATE=#{ivars.to_h.inspect}" puts "CURRENT=#{button.text} | NEW=#{display(board).to_s}" button.text = display(board).to_s board.update_status end end end Intro • Interface • State • Flow • Tradeoffs
138. ~/debugging $ bin/minesweeper STATE={:@button=>#<Tk::Button:0x007fedf282ee10 @path=".w00009">, :@mine_count=>1, :@mine=>false, :@neigh bors=>[8, 10, 28, 29, 30], :@clicked=>true} CURRENT= | NEW=1 Intro • Interface • State • Flow • Tradeoffs
139. ~/debugging $ bin/minesweeper STATE={:@button=>#<Tk::Button:0x007fedf282ee10 @path=".w00009">, :@mine_count=>1, :@mine=>false, :@neigh bors=>[8, 10, 28, 29, 30], :@clicked=>true} CURRENT= | NEW=1 Intro • Interface • State • Flow • Tradeoffs
140. ~/debugging $ bin/minesweeper STATE={:@button=>#<Tk::Button:0x007fedf282ee10 @path=".w00009">, :@mine_count=>1, :@mine=>false, :@neigh bors=>[8, 10, 28, 29, 30], :@clicked=>true} CURRENT= | NEW=1 Intro • Interface • State • Flow • Tradeoffs
141. ~/debugging $ bin/minesweeper STATE={:@button=>#<Tk::Button:0x007fedf282ee10 @path=".w00009">, :@mine_count=>1, :@mine=>false, :@neigh bors=>[8, 10, 28, 29, 30], :@clicked=>true} CURRENT= | NEW=1 Intro • Interface • State • Flow • Tradeoffs
142. ~/debugging $ bin/minesweeper STATE={:@button=>#<Tk::Button:0x007fedf282ee10 @path=".w00009">, :@mine_count=>1, :@mine=>false, :@neigh bors=>[8, 10, 28, 29, 30], :@clicked=>true} CURRENT= | NEW=1 Intro • Interface • State • Flow • Tradeoffs
143. What has been initialized at this point? Intro • Interface • State • Flow • Tradeoffs
144. ~/debugging $ bin/minesweeper ... board.rb:62:in `build_status_label': undefined method `count' for nil:NilClass (NoMethodError) from ... board.rb:17:in `start' from ... minesweeper.rb:7:in `start' from bin/minesweeper:7:in `<main>' Intro • Interface • State • Flow • Tradeoffs
145. ~/debugging $ bin/minesweeper ... board.rb:62:in `build_status_label': undefined method `count' for nil:NilClass (NoMethodError) from ... board.rb:17:in `start' from ... minesweeper.rb:7:in `start' from bin/minesweeper:7:in `<main>' Intro • Interface • State • Flow • Tradeoffs
146. module MineSweeper class Board attr_reader :width, :cells ... private def build_status_label(tk_root) initial_status = "#{cells.count(&:mines?)} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(column: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
147. module MineSweeper class Board attr_reader :width, :cells ... private def build_status_label(tk_root) initial_status = "#{cells.count(&:mines?)} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(column: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
148. module MineSweeper class Board attr_reader :width, :cells ... private def build_status_label(tk_root) require 'irb'; binding.irb initial_status = "#{cells.count(&:mines?)} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(column: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
149. module MineSweeper class Board attr_reader :width, :cells ... private def build_status_label(tk_root) require 'irb'; binding.irb initial_status = "#{cells.count(&:mines?)} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(column: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
150. module MineSweeper class Board attr_reader :width, :cells ... private def build_status_label(tk_root) require 'irb'; binding.irb initial_status = "#{cells.count(&:mines?)} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(column: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
151. ~/debugging $ bin/minesweeper irb(#<MineSweeper::Board:0x007ff858b14c90>):001:0> Intro • Interface • State • Flow • Tradeoffs
152. ~/debugging $ bin/minesweeper irb(#<...>):001:0> Intro • Interface • State • Flow • Tradeoffs
153. ~/debugging $ bin/minesweeper irb(#<...>):001:0> instance_variables => [:@width, :@height, :@mines] irb(#<...>):002:0> Intro • Interface • State • Flow • Tradeoffs
154. ~/debugging $ bin/minesweeper irb(#<...>):001:0> instance_variables => [:@width, :@height, :@mines] irb(#<...>):002:0> cells => nil irb(#<...>):003:0> Intro • Interface • State • Flow • Tradeoffs
155. How many objects are allocated in this method? Intro • Interface • State • Flow • Tradeoffs
156. module MineSweeper class Board attr_reader :mines, :cells, :status def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } cells.each(&:disable) 'You win!' else count = mines - cells.select(&:guessed?).count count.to_s + ' mines left' end end end end Intro • Interface • State • Flow • Tradeoffs
157. board = MineSweeper::Board.new(mines: 10) Intro • Interface • State • Flow • Tradeoffs
158. Status = Struct.new(:text) board = MineSweeper::Board.new(mines: 10) board.instance_eval do @status = Status.new end Intro • Interface • State • Flow • Tradeoffs
159. Status = Struct.new(:text) board = MineSweeper::Board.new(mines: 10) board.instance_eval do @status = Status.new @cells = [ MineSweeper::Cell.new(mine: true) ] end Intro • Interface • State • Flow • Tradeoffs
160. Status = Struct.new(:text) Button = Struct.new(:foobar) do def command(*) end def bind(*) end end board = MineSweeper::Board.new(mines: 10) board.instance_eval do @status = Status.new @cells = [ MineSweeper::Cell.new(mine: true, button: Button.new) ] end Intro • Interface • State • Flow • Tradeoffs
161. Status = Struct.new(:text) Button = Struct.new(:foobar) do def command(*) end def bind(*) end end board = MineSweeper::Board.new(mines: 10) board.instance_eval do @status = Status.new @cells = [ MineSweeper::Cell.new(mine: true, button: Button.new) ] end before = GC.stat[:total_allocated_objects] 10_000.times { board.update_status } puts GC.stat[:total_allocated_objects] - before Intro • Interface • State • Flow • Tradeoffs
162. Status = Struct.new(:text) Button = Struct.new(:foobar) do def command(*) end def bind(*) end end board = MineSweeper::Board.new(mines: 10) board.instance_eval do @status = Status.new @cells = [ MineSweeper::Cell.new(mine: true, button: Button.new) ] end before = GC.stat[:total_allocated_objects] 10_000.times { board.update_status } puts GC.stat[:total_allocated_objects] - before Intro • Interface • State • Flow • Tradeoffs
163. Status = Struct.new(:text) Button = Struct.new(:foobar) do def command(*) end def bind(*) end end board = MineSweeper::Board.new(mines: 10) board.instance_eval do @status = Status.new @cells = [ MineSweeper::Cell.new(mine: true, button: Button.new) ] end before = GC.stat[:total_allocated_objects] 10_000.times { board.update_status } puts GC.stat[:total_allocated_objects] - before Intro • Interface • State • Flow • Tradeoffs
164. Status = Struct.new(:text) Button = Struct.new(:foobar) do def command(*) end def bind(*) end end board = MineSweeper::Board.new(mines: 10) board.instance_eval do @status = Status.new @cells = [ MineSweeper::Cell.new(mine: true, button: Button.new) ] end before = GC.stat[:total_allocated_objects] 10_000.times { board.update_status } puts GC.stat[:total_allocated_objects] - before Intro • Interface • State • Flow • Tradeoffs
165. Status = Struct.new(:text) Button = Struct.new(:foobar) do def command(*) end def bind(*) end end board = MineSweeper::Board.new(mines: 10) board.instance_eval do @status = Status.new @cells = [ MineSweeper::Cell.new(mine: true, button: Button.new) ] end before = GC.stat[:total_allocated_objects] 10_000.times { board.update_status } puts GC.stat[:total_allocated_objects] - before Intro • Interface • State • Flow • Tradeoffs
166. Status = Struct.new(:text) Button = Struct.new(:foobar) do def command(*) end def bind(*) end end board = MineSweeper::Board.new(mines: 10) board.instance_eval do @status = Status.new @cells = [ MineSweeper::Cell.new(mine: true, button: Button.new) ] end before = GC.stat[:total_allocated_objects] 10_000.times { board.update_status } puts GC.stat[:total_allocated_objects] - before Intro • Interface • State • Flow • Tradeoffs
167. ~/debugging $ ruby -Ilib -rminesweeper examples/gc.rb 70001 ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
168. module MineSweeper class Board attr_reader :mines, :cells, :status def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } cells.each(&:disable) 'You win!' else count = mines - cells.select(&:guessed?).count count.to_s + ' mines left' end end end end Intro • Interface • State • Flow • Tradeoffs
169. module MineSweeper class Board attr_reader :mines, :cells, :status def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } cells.each(&:disable) 'You win!' else count = mines - cells.select(&:guessed?).count count.to_s + ' mines left' end end end end Intro • Interface • State • Flow • Tradeoffs
170. module MineSweeper class Board attr_reader :mines, :cells, :status def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } cells.each(&:disable) 'You win!' else count = mines - cells.count(&:guessed?) count.to_s + ' mines left' end end end end Intro • Interface • State • Flow • Tradeoffs
171. module MineSweeper class Board attr_reader :mines, :cells, :status def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } cells.each(&:disable) 'You win!' else count = mines - cells.count(&:guessed?) "#{count} mines left" end end end end Intro • Interface • State • Flow • Tradeoffs
172. ~/debugging $ ruby -Ilib -rminesweeper examples/gc.rb 50001 ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
173. Lessons learned Intro • Interface • State • Flow • Tradeoffs
174. Take advantage of Ruby's quick feedback loops and flexibility. Intro • Interface • State • Flow • Tradeoffs
175. Your ability to see into your program’s state at any point is one of your strongest tools in debugging. Intro • Interface • State • Flow • Tradeoffs
176. Flow problems Intro • Interface • State • Flow • Tradeoffs
177. Flow problems occur when you don’t know how the ruby interpreter got to or left a location in code and its associated state. Intro • Interface • State • Flow • Tradeoffs
178. How did the interpreter get here? Intro • Interface • State • Flow • Tradeoffs
179. How did the interpreter get here? Where does the interpreter go from here? Intro • Interface • State • Flow • Tradeoffs
180. How did the interpreter get here? Where does the interpreter go from here? How did this object get here? Intro • Interface • State • Flow • Tradeoffs
181. How did the interpreter get here? Where does the interpreter go from here? How did this object get here? Where is this object being mutated? Intro • Interface • State • Flow • Tradeoffs
182. How did the interpreter get here? Where does the interpreter go from here? How did this object get here? Where is this object being mutated? When does this instance variable get set? Intro • Interface • State • Flow • Tradeoffs
183. How did the interpreter get here? Intro • Interface • State • Flow • Tradeoffs
184. module MineSweeper class Board ... def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } cells.each(&:disable) 'You win!' else count = mines - cells.count(&:guessed?) "#{count} mines left" end end end end Intro • Interface • State • Flow • Tradeoffs
185. module MineSweeper class Board ... def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } cells.each(&:disable) 'You win!' else count = mines - cells.count(&:guessed?) "#{count} mines left" end end end end Intro • Interface • State • Flow • Tradeoffs
186. module MineSweeper class Board ... def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } puts caller cells.each(&:disable) 'You win!' else count = mines - cells.count(&:guessed?) "#{count} mines left" end end end end Intro • Interface • State • Flow • Tradeoffs
187. module MineSweeper class Board ... def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } puts caller cells.each(&:disable) 'You win!' else count = mines - cells.count(&:guessed?) "#{count} mines left" end end end end Intro • Interface • State • Flow • Tradeoffs
188. ~/debugging $ bin/minesweeper ... cell.rb:54:in `update' ... cell.rb:39:in `toggle_mine' ... cell.rb:18:in `block in initialize' ... tk-0.1.2/lib/tk/event.rb:495:in `eval_cmd' ... tk-0.1.2/lib/tk/event.rb:495:in `block in install_bind_for_event_class' ... tk-0.1.2/lib/tk.rb:1456:in `eval_cmd' ... tk-0.1.2/lib/tk.rb:1456:in `cb_eval' ... tk-0.1.2/lib/tk.rb:1403:in `call' ... tk-0.1.2/lib/tk.rb:1607:in `block in callback' ... tk-0.1.2/lib/tk.rb:1606:in `catch' ... tk-0.1.2/lib/tk.rb:1606:in `callback' ... tk-0.1.2/lib/tk.rb:1871:in `mainloop' ... tk-0.1.2/lib/tk.rb:1871:in `mainloop' ... board.rb:19:in `start' ... minesweeper.rb:7:in `start' bin/minesweeper:7:in `<main>' Intro • Interface • State • Flow • Tradeoffs
189. ~/debugging $ bin/minesweeper ... cell.rb:54:in `update' ... cell.rb:39:in `toggle_mine' ... cell.rb:18:in `block in initialize' ... tk-0.1.2/lib/tk/event.rb:495:in `eval_cmd' ... tk-0.1.2/lib/tk/event.rb:495:in `block in install_bind_for_event_class' ... tk-0.1.2/lib/tk.rb:1456:in `eval_cmd' ... tk-0.1.2/lib/tk.rb:1456:in `cb_eval' ... tk-0.1.2/lib/tk.rb:1403:in `call' ... tk-0.1.2/lib/tk.rb:1607:in `block in callback' ... tk-0.1.2/lib/tk.rb:1606:in `catch' ... tk-0.1.2/lib/tk.rb:1606:in `callback' ... tk-0.1.2/lib/tk.rb:1871:in `mainloop' ... tk-0.1.2/lib/tk.rb:1871:in `mainloop' ... board.rb:19:in `start' ... minesweeper.rb:7:in `start' bin/minesweeper:7:in `<main>' Intro • Interface • State • Flow • Tradeoffs
190. module MineSweeper class Board ... def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } puts caller cells.each(&:disable) 'You win!' else count = mines - cells.count(&:guessed?) "#{count} mines left" end end end end Intro • Interface • State • Flow • Tradeoffs
191. module MineSweeper class Board ... def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } puts caller.grep(Regexp.new(Regexp.quote(__dir__))) cells.each(&:disable) 'You win!' else count = mines - cells.count(&:guessed?) "#{count} mines left" end end end end Intro • Interface • State • Flow • Tradeoffs
192. module MineSweeper class Board ... def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } puts caller.grep(Regexp.new(Regexp.quote(__dir__))) cells.each(&:disable) 'You win!' else count = mines - cells.count(&:guessed?) "#{count} mines left" end end end end Intro • Interface • State • Flow • Tradeoffs
193. module MineSweeper class Board ... def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } puts caller.grep(Regexp.new(Regexp.quote(__dir__))) cells.each(&:disable) 'You win!' else count = mines - cells.count(&:guessed?) "#{count} mines left" end end end end Intro • Interface • State • Flow • Tradeoffs
194. ~/debugging $ bin/minesweeper ... cell.rb:54:in `update' ... cell.rb:39:in `toggle_mine' ... cell.rb:18:in `block in initialize' ... board.rb:19:in `start' ... minesweeper.rb:7:in `start' Intro • Interface • State • Flow • Tradeoffs
195. Where does the interpreter go from here? Intro • Interface • State • Flow • Tradeoffs
196. require 'tk' require 'minesweeper/board' require 'minesweeper/cell' module MineSweeper DEFAULTS = { width: 20, height: 10, mines: 10 } def self.start(args = {}) Board.new(DEFAULTS.merge(args)).start end end Intro • Interface • State • Flow • Tradeoffs
197. require 'tk' require 'minesweeper/board' require 'minesweeper/cell' module MineSweeper DEFAULTS = { width: 20, height: 10, mines: 10 } def self.start(args = {}) TracePoint.new(:call) do |tp| puts "#{tp.path}:#{tp.lineno}" end.enable Board.new(DEFAULTS.merge(args)).start end end Intro • Interface • State • Flow • Tradeoffs
198. require 'tk' require 'minesweeper/board' require 'minesweeper/cell' module MineSweeper DEFAULTS = { width: 20, height: 10, mines: 10 } def self.start(args = {}) TracePoint.new(:call) do |tp| puts "#{tp.path}:#{tp.lineno}" end.enable Board.new(DEFAULTS.merge(args)).start end end Intro • Interface • State • Flow • Tradeoffs
199. require 'tk' require 'minesweeper/board' require 'minesweeper/cell' module MineSweeper DEFAULTS = { width: 20, height: 10, mines: 10 } def self.start(args = {}) TracePoint.new(:call) do |tp| puts "#{tp.path}:#{tp.lineno}" end.enable Board.new(DEFAULTS.merge(args)).start end end Intro • Interface • State • Flow • Tradeoffs
200. require 'tk' require 'minesweeper/board' require 'minesweeper/cell' module MineSweeper DEFAULTS = { width: 20, height: 10, mines: 10 } def self.start(args = {}) TracePoint.new(:call) do |tp| puts "#{tp.path}:#{tp.lineno}" end.enable Board.new(DEFAULTS.merge(args)).start end end Intro • Interface • State • Flow • Tradeoffs
201. require 'tk' require 'minesweeper/board' require 'minesweeper/cell' module MineSweeper DEFAULTS = { width: 20, height: 10, mines: 10 } def self.start(args = {}) TracePoint.new(:call) do |tp| puts "#{tp.path}:#{tp.lineno}" end.enable Board.new(DEFAULTS.merge(args)).start end end Intro • Interface • State • Flow • Tradeoffs
202. ~/debugging $ bin/minesweeper ... board.rb:5 ... board.rb:15 ... ruby/2.4.0/rubygems/core_ext/kernel_require.rb:39 ... ruby/2.4.0/monitor.rb:185 ... ruby/2.4.0/rubygems.rb:1240 ... ruby/2.4.0/rubygems.rb:1003 ... ruby/2.4.0/rubygems/specification.rb:1299 ... ruby/2.4.0/monitor.rb:197 ... ruby/2.4.0/monitor.rb:247 ... ruby/2.4.0/rubygems/core_ext/kernel_require.rb:39 ... ruby/2.4.0/monitor.rb:185 ... ruby/2.4.0/rubygems.rb:1240 ... ruby/2.4.0/rubygems.rb:1003 ... ruby/2.4.0/rubygems/specification.rb:1299 ... Intro • Interface • State • Flow • Tradeoffs
203. ~/debugging $ bin/minesweeper ... board.rb:5 ... board.rb:15 ... ruby/2.4.0/rubygems/core_ext/kernel_require.rb:39 ... ruby/2.4.0/monitor.rb:185 ... ruby/2.4.0/rubygems.rb:1240 ... ruby/2.4.0/rubygems.rb:1003 ... ruby/2.4.0/rubygems/specification.rb:1299 ... ruby/2.4.0/monitor.rb:197 ... ruby/2.4.0/monitor.rb:247 ... ruby/2.4.0/rubygems/core_ext/kernel_require.rb:39 ... ruby/2.4.0/monitor.rb:185 ... ruby/2.4.0/rubygems.rb:1240 ... ruby/2.4.0/rubygems.rb:1003 ... ruby/2.4.0/rubygems/specification.rb:1299 ... Intro • Interface • State • Flow • Tradeoffs
204. require 'tk' require 'minesweeper/board' require 'minesweeper/cell' module MineSweeper DEFAULTS = { width: 20, height: 10, mines: 10 } def self.start(args = {}) TracePoint.new(:call) do |tp| puts "#{tp.path}:#{tp.lineno}" end.enable Board.new(DEFAULTS.merge(args)).start end end Intro • Interface • State • Flow • Tradeoffs
205. require 'tk' require 'minesweeper/board' require 'minesweeper/cell' module MineSweeper DEFAULTS = { width: 20, height: 10, mines: 10 } def self.start(args = {}) TracePoint.new(:call) do |tp| puts "#{tp.path}:#{tp.lineno}" if tp.path.include?(__dir__) end.enable Board.new(DEFAULTS.merge(args)).start end end Intro • Interface • State • Flow • Tradeoffs
206. ~/debugging $ bin/minesweeper ... board.rb:5 ... board.rb:15 ... board.rb:40 ... board.rb:86 ... board.rb:73 ... board.rb:86 ... board.rb:86 ... board.rb:86 ... board.rb:86 ... board.rb:86 ... board.rb:86 ... board.rb:86 ... board.rb:86 ... cell.rb:10 ... board.rb:86 ... board.rb:73 ... Intro • Interface • State • Flow • Tradeoffs
207. How did this object get here? Intro • Interface • State • Flow • Tradeoffs
208. module MineSweeper class Cell ... def initialize(args = {}) @button = args[:button] @mine_count = args[:mine_count] @mine = args[:mine] @neighbors = args[:neighbors] board = args[:board] @button.command(-> { click(board) }) @button.bind('ButtonRelease-2', -> { toggle_mine(board) }) end end end Intro • Interface • State • Flow • Tradeoffs
209. module MineSweeper class Cell ... def initialize(args = {}) @button = args[:button] @mine_count = args[:mine_count] @mine = args[:mine] @neighbors = args[:neighbors] board = args[:board] @button.command(-> { click(board) }) @button.bind('ButtonRelease-2', -> { toggle_mine(board) }) sourcefile = ObjectSpace.allocation_sourcefile(@button) sourceline = ObjectSpace.allocation_sourceline(@button) puts "#{sourcefile}:#{sourceline}" end end end require 'objspace' ObjectSpace.trace_object_allocations_start Intro • Interface • State • Flow • Tradeoffs
210. module MineSweeper class Cell ... def initialize(args = {}) @button = args[:button] @mine_count = args[:mine_count] @mine = args[:mine] @neighbors = args[:neighbors] board = args[:board] @button.command(-> { click(board) }) @button.bind('ButtonRelease-2', -> { toggle_mine(board) }) sourcefile = ObjectSpace.allocation_sourcefile(@button) sourceline = ObjectSpace.allocation_sourceline(@button) puts "#{sourcefile}:#{sourceline}" end end end require 'objspace' ObjectSpace.trace_object_allocations_start Intro • Interface • State • Flow • Tradeoffs
211. module MineSweeper class Cell ... def initialize(args = {}) @button = args[:button] @mine_count = args[:mine_count] @mine = args[:mine] @neighbors = args[:neighbors] board = args[:board] @button.command(-> { click(board) }) @button.bind('ButtonRelease-2', -> { toggle_mine(board) }) sourcefile = ObjectSpace.allocation_sourcefile(@button) sourceline = ObjectSpace.allocation_sourceline(@button) puts "#{sourcefile}:#{sourceline}" end end end require 'objspace' ObjectSpace.trace_object_allocations_start Intro • Interface • State • Flow • Tradeoffs
212. module MineSweeper class Cell ... def initialize(args = {}) @button = args[:button] @mine_count = args[:mine_count] @mine = args[:mine] @neighbors = args[:neighbors] board = args[:board] @button.command(-> { click(board) }) @button.bind('ButtonRelease-2', -> { toggle_mine(board) }) sourcefile = ObjectSpace.allocation_sourcefile(@button) sourceline = ObjectSpace.allocation_sourceline(@button) puts "#{sourcefile}:#{sourceline}" end end end require 'objspace' ObjectSpace.trace_object_allocations_start Intro • Interface • State • Flow • Tradeoffs
213. ~/debugging $ bin/minesweeper ... board.rb:48 ... board.rb:48 ... board.rb:48 ... board.rb:48 ... board.rb:48 ... board.rb:48 ... Intro • Interface • State • Flow • Tradeoffs
214. module MineSweeper class Board def build_cells(tk_root) ... height.times.flat_map do |ycoord| width.times.map do |xcoord| index = index_for(ycoord, xcoord) neighbors = neighbors_for(ycoord, xcoord) button = TkButton.new(tk_root) do grid(column: xcoord, row: ycoord + 1) end ... end end end end end Intro • Interface • State • Flow • Tradeoffs
215. module MineSweeper class Board def build_cells(tk_root) ... height.times.flat_map do |ycoord| width.times.map do |xcoord| index = index_for(ycoord, xcoord) neighbors = neighbors_for(ycoord, xcoord) button = TkButton.new(tk_root) do grid(column: xcoord, row: ycoord + 1) end ... end end end end end Intro • Interface • State • Flow • Tradeoffs
216. Where is this object being mutated? Intro • Interface • State • Flow • Tradeoffs
217. Intro • Interface • State • Flow • Tradeoffs
218. module MineSweeper class Board attr_reader :cells def click(index) cells[index].click(self) end def start tk_root = TkRoot.new { title 'MineSweeper' } @cells = build_cells(tk_root) @status = build_status_label(tk_root) Tk.mainloop end ... end end Intro • Interface • State • Flow • Tradeoffs
219. module MineSweeper class Board attr_reader :cells def click(index) cells[index].click(self) end def start tk_root = TkRoot.new { title 'MineSweeper' } @cells = build_cells(tk_root) @status = build_status_label(tk_root) Tk.mainloop end ... end end Intro • Interface • State • Flow • Tradeoffs
220. module MineSweeper class Board attr_reader :cells def click(index) cells[index].click(self) end def start tk_root = TkRoot.new { title 'MineSweeper' } @cells = build_cells(tk_root) @status = build_status_label(tk_root) Tk.mainloop end ... end end Intro • Interface • State • Flow • Tradeoffs
221. module MineSweeper class Board attr_reader :cells def click(index) cells[index].click(self) end def start tk_root = TkRoot.new { title 'MineSweeper' } @cells = build_cells(tk_root) @cells.freeze @status = build_status_label(tk_root) Tk.mainloop end ... end end Intro • Interface • State • Flow • Tradeoffs
222. Intro • Interface • State • Flow • Tradeoffs
223. module MineSweeper class Board attr_reader :cells ... def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } cells.each(&:disable) 'You win!' else cells.select!(&:guessed?) count = mines - cells.count "#{count} mines left" end end end end Intro • Interface • State • Flow • Tradeoffs
224. module MineSweeper class Board attr_reader :cells ... def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } cells.each(&:disable) 'You win!' else cells.select!(&:guessed?) count = mines - cells.count "#{count} mines left" end end end end Intro • Interface • State • Flow • Tradeoffs
225. module MineSweeper class Board attr_reader :cells ... def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } cells.each(&:disable) 'You win!' else count = mines - cells.count(&:guessed?) "#{count} mines left" end end end end Intro • Interface • State • Flow • Tradeoffs
226. module MineSweeper class Board attr_reader :cells ... def update_status status.text = if cells.any? { |cell| cell.mine? && cell.clicked? } cells.each(&:disable) 'You lose!' elsif cells.all? { |cell| !cell.mine? || (cell.mine? && cell.guessed?) } cells.each(&:disable) 'You win!' else count = mines - cells.count(&:guessed?) "#{count} mines left" end end end end Intro • Interface • State • Flow • Tradeoffs
227. When does this instance variable get set? Intro • Interface • State • Flow • Tradeoffs
228. ~/debugging $ bin/minesweeper ... board.rb:62:in `build_status_label': undefined method `count' for nil:NilClass (NoMethodError) from ... board.rb:17:in `start' from ... minesweeper.rb:7:in `start' from bin/minesweeper:7:in `<main>' Intro • Interface • State • Flow • Tradeoffs
229. module MineSweeper class Board attr_reader :cells def build_status_label(tk_root) require 'irb'; binding.irb initial_status = "#{cells.count(&:mines?)} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(column: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
230. module MineSweeper class Board attr_reader :cells def build_status_label(tk_root) initial_status = "#{cells.count(&:mines?)} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(column: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
231. module MineSweeper class Board attr_reader :cells def build_status_label(tk_root) @cells = [] initial_status = "#{cells.count(&:mines?)} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(column: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
232. Intro • Interface • State • Flow • Tradeoffs
233. module MineSweeper class Board attr_reader :cells def build_status_label(tk_root) @cells = [] initial_status = "#{cells.count(&:mines?)} mines left" column_span = width TkLabel.new(tk_root) do text initial_status grid(column: 0, row: 0, columnspan: column_span) end end end end Intro • Interface • State • Flow • Tradeoffs
234. module MineSweeper class Board attr_reader :cells def build_status_label(tk_root) cells = @cells = [] TracePoint.new(:line) do |tp| if (tp.path == __FILE__ && tp.binding.eval('self.class') == self.class && tp.binding.eval('@cells') != cells) puts "#{tp.path}:#{tp.lineno - 1}" exit end end.enable initial_status = "#{cells.count(&:mines?)} mines left” ... end end end Intro • Interface • State • Flow • Tradeoffs
235. module MineSweeper class Board attr_reader :cells def build_status_label(tk_root) cells = @cells = [] TracePoint.new(:line) do |tp| if (tp.path == __FILE__ && tp.binding.eval('self.class') == self.class && tp.binding.eval('@cells') != cells) puts "#{tp.path}:#{tp.lineno - 1}" exit end end.enable initial_status = "#{cells.count(&:mines?)} mines left” ... end end end Intro • Interface • State • Flow • Tradeoffs
236. module MineSweeper class Board attr_reader :cells def build_status_label(tk_root) cells = @cells = [] TracePoint.new(:line) do |tp| if (tp.path == __FILE__ && tp.binding.eval('self.class') == self.class && tp.binding.eval('@cells') != cells) puts "#{tp.path}:#{tp.lineno - 1}" exit end end.enable initial_status = "#{cells.count(&:mines?)} mines left” ... end end end Intro • Interface • State • Flow • Tradeoffs
237. module MineSweeper class Board attr_reader :cells def build_status_label(tk_root) cells = @cells = [] TracePoint.new(:line) do |tp| if (tp.path == __FILE__ && tp.binding.eval('self.class') == self.class && tp.binding.eval('@cells') != cells) puts "#{tp.path}:#{tp.lineno - 1}" exit end end.enable initial_status = "#{cells.count(&:mines?)} mines left” ... end end end Intro • Interface • State • Flow • Tradeoffs
238. module MineSweeper class Board attr_reader :cells def build_status_label(tk_root) cells = @cells = [] TracePoint.new(:line) do |tp| if (tp.path == __FILE__ && tp.binding.eval('self.class') == self.class && tp.binding.eval('@cells') != cells) puts "#{tp.path}:#{tp.lineno - 1}" exit end end.enable initial_status = "#{cells.count(&:mines?)} mines left” ... end end end Intro • Interface • State • Flow • Tradeoffs
239. module MineSweeper class Board attr_reader :cells def build_status_label(tk_root) cells = @cells = [] TracePoint.new(:line) do |tp| if (tp.path == __FILE__ && tp.binding.eval('self.class') == self.class && tp.binding.eval('@cells') != cells) puts "#{tp.path}:#{tp.lineno - 1}" exit end end.enable initial_status = "#{cells.count(&:mines?)} mines left” ... end end end Intro • Interface • State • Flow • Tradeoffs
240. ~/debugging $ bin/minesweeper ... board.rb:18 ~/debugging $ Intro • Interface • State • Flow • Tradeoffs
241. module MineSweeper class Board attr_reader :cells, :status ... def start tk_root = TkRoot.new { title 'MineSweeper' } @status = build_status_label(tk_root) @cells = build_cells(tk_root) Tk.mainloop end end end Intro • Interface • State • Flow • Tradeoffs
242. module MineSweeper class Board attr_reader :cells, :status ... def start tk_root = TkRoot.new { title 'MineSweeper' } @status = build_status_label(tk_root) @cells = build_cells(tk_root) Tk.mainloop end end end Intro • Interface • State • Flow • Tradeoffs
243. module MineSweeper class Board attr_reader :cells, :status ... def start tk_root = TkRoot.new { title 'MineSweeper' } @status = build_status_label(tk_root) @cells = build_cells(tk_root) Tk.mainloop end end end Intro • Interface • State • Flow • Tradeoffs
244. module MineSweeper class Board attr_reader :cells, :status ... def start tk_root = TkRoot.new { title 'MineSweeper' } @cells = build_cells(tk_root) @status = build_status_label(tk_root) Tk.mainloop end end end Intro • Interface • State • Flow • Tradeoffs
245. Lessons learned Intro • Interface • State • Flow • Tradeoffs
246. For large projects, ruby requires effort to follow the flow. Intro • Interface • State • Flow • Tradeoffs
247. For new projects, stack traces are easy to generate and follow. Intro • Interface • State • Flow • Tradeoffs
248. Ruby's tradeoffs Intro • Interface • State • Flow • Tradeoffs
249. Compiler niceties for introspection Intro • Interface • State • Flow • Tradeoffs
250. Compiler niceties for introspection Out of the box speed for flexibility Intro • Interface • State • Flow • Tradeoffs
251. Compiler niceties for introspection Out of the box speed for flexibility Maintenance cost for start-up cost Intro • Interface • State • Flow • Tradeoffs
252. Interface Out of the box speed for flexibility Maintenance cost for start-up cost Intro • Interface • State • Flow • Tradeoffs
253. Interface State Maintenance cost for start-up cost Intro • Interface • State • Flow • Tradeoffs
254. Interface State Flow Intro • Interface • State • Flow • Tradeoffs
255. Practical Debugging github.com/kddeisz/debugging Kevin Deisz @kddeisz
256. A Comprehensive Guide to Debugging Rails
 https://www.jackkinsella.ie/articles/a-comprehensive-guide-to-debugging-rails Debugging memory leaks in Ruby
 https://samsaffron.com/archive/2015/03/31/debugging-memory-leaks-in-ruby Debugging Rails Applications
 http://guides.rubyonrails.org/debugging_rails_applications.html Debugging Rails Applications in Development
 http://nofail.de/2013/10/debugging-rails-applications-in-development/ I am a puts debuggerer
 https://tenderlovemaking.com/2016/02/05/i-am-a-puts-debuggerer.html Ruby Debugging Magic Cheat Sheet
 http://www.schneems.com/2016/01/25/ruby-debugging-magic-cheat-sheet.html There’s More to Ruby Debugging Than puts()
 https://engineering.shopify.com/17489080-theres-more-to-ruby-debugging- than-puts References