Practical Debugging - Speaker Deck

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Practical Debugging

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~/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 `’ ~/debugging $ Intro • Interface • State • Flow • Tradeoffs

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Intro • Interface • State • Flow • Tradeoffs

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Remain calm Intro • Interface • State • Flow • Tradeoffs

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What would StackOverflow do? Intro • Interface • State • Flow • Tradeoffs

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What would StackOverflow do? #WWSOD Intro • Interface • State • Flow • Tradeoffs

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Use pry Use byebug Intro • Interface • State • Flow • Tradeoffs

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Use pry Use byebug Intro • Interface • State • Flow • Tradeoffs

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Use pry Use byebug Intro • Interface • State • Flow • Tradeoffs

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Use pry Use byebug Intro • Interface • State • Flow • Tradeoffs

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Use pry Use byebug Intro • Interface • State • Flow • Tradeoffs

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Use pry Use the rub Intro • Interface • State • Flow • Tradeoffs

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Use pry Use the ruby debugger Intro • Interface • State • Flow • Tradeoffs

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Use pry Use the ruby debugger Intro • Interface • State • Flow • Tradeoffs

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Use pry Use the ruby debugger Intro • Interface • State • Flow • Tradeoffs

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Use pry Use the ruby debugger Intro • Interface • State • Flow • Tradeoffs

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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

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You don’t get style points in debugging. Intro • Interface • State • Flow • Tradeoffs

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The ruby standard library has every tool you need to debug effectively. Intro • Interface • State • Flow • Tradeoffs

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Debugging Intro • Interface • State • Flow • Tradeoffs

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What kind of problem are you solving? Intro • Interface • State • Flow • Tradeoffs

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Interface problem Intro • Interface • State • Flow • Tradeoffs

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Interface problem State problem Intro • Interface • State • Flow • Tradeoffs

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Interface problem State problem Flow problem Intro • Interface • State • Flow • Tradeoffs

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Interface problems Intro • Interface • State • Flow • Tradeoffs

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Interface problems occur when you don’t understand the dependent structure of methods or constants. Intro • Interface • State • Flow • Tradeoffs

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Why is this thing nil? Intro • Interface • State • Flow • Tradeoffs

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Why is this thing nil? Why can’t I call the method I want? Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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Why is this thing nil? Intro • Interface • State • Flow • Tradeoffs

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~/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 `' Intro • Interface • State • Flow • Tradeoffs

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~/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 `' Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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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

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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

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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

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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 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

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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

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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

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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

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Why can’t I call the method I want? Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/minesweeper ... tk-0.1.2/lib/tk.rb:4984:in `rescue in method_missing': unknown option 'mines' for # (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 `’ ~/debugging $ Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/minesweeper ... tk-0.1.2/lib/tk.rb:4984:in `rescue in method_missing': unknown option 'mines' for # (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 `’ ~/debugging $ Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/minesweeper ... tk-0.1.2/lib/tk.rb:4984:in `rescue in method_missing': unknown option 'mines' for # (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 `’ ~/debugging $ Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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~/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

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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

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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

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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

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What are the constants I can reference? Intro • Interface • State • Flow • Tradeoffs

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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

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~/debugging $ ruby examples/module_nesting_1.rb examples/module_nesting_1.rb:7:in `': uninitialized constant MineSweeper::Base (NameError) from examples/module_nesting_1.rb:1:in `' ~/debugging $ Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ ruby examples/module_nesting_1.rb examples/module_nesting_1.rb:7:in `': uninitialized constant MineSweeper::Base (NameError) from examples/module_nesting_1.rb:1:in `' ~/debugging $ Intro • Interface • State • Flow • Tradeoffs

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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

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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

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~/debugging $ ruby examples/module_nesting_1.rb MineSweeper ~/debugging $ Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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~/debugging $ ruby examples/module_nesting_2.rb MineSweeper::Cell MineSweeper ~/debugging $ Intro • Interface • State • Flow • Tradeoffs

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What can this object see and do? Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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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

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~/debugging $ ruby -Ilib -rminesweeper examples/constants.rb MineSweeper MineSweeper::Board MineSweeper::Cell ~/debugging $ Intro • Interface • State • Flow • Tradeoffs

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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

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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

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~/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

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~/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

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~/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

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~/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

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~/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

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~/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

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~/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

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~/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

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Oh god oh god what is this gem even doing? Intro • Interface • State • Flow • Tradeoffs

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~/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 `' Intro • Interface • State • Flow • Tradeoffs

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~/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 `' Intro • Interface • State • Flow • Tradeoffs

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~/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 `' Intro • Interface • State • Flow • Tradeoffs

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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

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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

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~/debugging $ bin/console irb(main):001:0> Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(:grid) => # irb(main):002:0> Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(: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

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~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(: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

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~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(: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

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~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(: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

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class TkWindow

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class TkWindow

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~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(: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

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~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(: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) => # irb(main):004:0> Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(: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) => # 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

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~/debugging $ bin/console irb(main):001:0> method = TkLabel.instance_method(: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) => # 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

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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

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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

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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

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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

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~/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

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~/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

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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

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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

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~/debugging $ bundle exec gem pristine tk Restoring gems to pristine condition... Restored tk-0.1.2 ~/debugging $ Intro • Interface • State • Flow • Tradeoffs

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Lessons learned Intro • Interface • State • Flow • Tradeoffs

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Account for every return type Intro • Interface • State • Flow • Tradeoffs

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Account for constant and method lookup Intro • Interface • State • Flow • Tradeoffs

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Take advantage of constant and method introspection Intro • Interface • State • Flow • Tradeoffs

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Take advantage of the fact that gems aren't bytecode Intro • Interface • State • Flow • Tradeoffs

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State problems Intro • Interface • State • Flow • Tradeoffs

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State problems occur when the assumptions you made about the current state of the program are incorrect. Intro • Interface • State • Flow • Tradeoffs

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How does this value change at this point? Intro • Interface • State • Flow • Tradeoffs

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How does this value change at this point? What has been initialized at this point? Intro • Interface • State • Flow • Tradeoffs

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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

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How does this value change at this point? Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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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

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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

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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

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~/debugging $ bin/minesweeper STATE={:@button=>#, :@mine_count=>1, :@mine=>false, :@neigh bors=>[8, 10, 28, 29, 30], :@clicked=>true} CURRENT= | NEW=1 Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/minesweeper STATE={:@button=>#, :@mine_count=>1, :@mine=>false, :@neigh bors=>[8, 10, 28, 29, 30], :@clicked=>true} CURRENT= | NEW=1 Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/minesweeper STATE={:@button=>#, :@mine_count=>1, :@mine=>false, :@neigh bors=>[8, 10, 28, 29, 30], :@clicked=>true} CURRENT= | NEW=1 Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/minesweeper STATE={:@button=>#, :@mine_count=>1, :@mine=>false, :@neigh bors=>[8, 10, 28, 29, 30], :@clicked=>true} CURRENT= | NEW=1 Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/minesweeper STATE={:@button=>#, :@mine_count=>1, :@mine=>false, :@neigh bors=>[8, 10, 28, 29, 30], :@clicked=>true} CURRENT= | NEW=1 Intro • Interface • State • Flow • Tradeoffs

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What has been initialized at this point? Intro • Interface • State • Flow • Tradeoffs

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~/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 `' Intro • Interface • State • Flow • Tradeoffs

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~/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 `' Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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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

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~/debugging $ bin/minesweeper irb(#):001:0> Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/minesweeper irb(#<...>):001:0> Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/minesweeper irb(#<...>):001:0> instance_variables => [:@width, :@height, :@mines] irb(#<...>):002:0> Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/minesweeper irb(#<...>):001:0> instance_variables => [:@width, :@height, :@mines] irb(#<...>):002:0> cells => nil irb(#<...>):003:0> Intro • Interface • State • Flow • Tradeoffs

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How many objects are allocated in this method? Intro • Interface • State • Flow • Tradeoffs

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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

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board = MineSweeper::Board.new(mines: 10) Intro • Interface • State • Flow • Tradeoffs

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Status = Struct.new(:text) board = MineSweeper::Board.new(mines: 10) board.instance_eval do @status = Status.new end Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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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

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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

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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

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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

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~/debugging $ ruby -Ilib -rminesweeper examples/gc.rb 70001 ~/debugging $ Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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~/debugging $ ruby -Ilib -rminesweeper examples/gc.rb 50001 ~/debugging $ Intro • Interface • State • Flow • Tradeoffs

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Lessons learned Intro • Interface • State • Flow • Tradeoffs

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Take advantage of Ruby's quick feedback loops and flexibility. Intro • Interface • State • Flow • Tradeoffs

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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

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Flow problems Intro • Interface • State • Flow • Tradeoffs

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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

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How did the interpreter get here? Intro • Interface • State • Flow • Tradeoffs

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How did the interpreter get here? Where does the interpreter go from here? Intro • Interface • State • Flow • Tradeoffs

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How did the interpreter get here? Where does the interpreter go from here? How did this object get here? Intro • Interface • State • Flow • Tradeoffs

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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

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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

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How did the interpreter get here? Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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~/debugging $ bin/minesweeper ... cell.rb:54:in ùpdate' ... cell.rb:39:in `toggle_mine' ... cell.rb:18:in `block in initialize' ... tk-0.1.2/lib/tk/event.rb:495:in èval_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 èval_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 `' Intro • Interface • State • Flow • Tradeoffs

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~/debugging $ bin/minesweeper ... cell.rb:54:in ùpdate' ... cell.rb:39:in `toggle_mine' ... cell.rb:18:in `block in initialize' ... tk-0.1.2/lib/tk/event.rb:495:in èval_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 èval_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 `' Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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~/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

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Where does the interpreter go from here? Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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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

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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

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~/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

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~/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

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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

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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

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~/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

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How did this object get here? Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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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

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~/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

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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

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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

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Where is this object being mutated? Intro • Interface • State • Flow • Tradeoffs

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Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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When does this instance variable get set? Intro • Interface • State • Flow • Tradeoffs

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~/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 `' Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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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

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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

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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

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~/debugging $ bin/minesweeper ... board.rb:18 ~/debugging $ Intro • Interface • State • Flow • Tradeoffs

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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

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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

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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

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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

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Lessons learned Intro • Interface • State • Flow • Tradeoffs

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For large projects, ruby requires effort to follow the flow. Intro • Interface • State • Flow • Tradeoffs

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For new projects, stack traces are easy to generate and follow. Intro • Interface • State • Flow • Tradeoffs

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Ruby's tradeoffs Intro • Interface • State • Flow • Tradeoffs

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Compiler niceties for introspection Intro • Interface • State • Flow • Tradeoffs

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Compiler niceties for introspection Out of the box speed for flexibility Intro • Interface • State • Flow • Tradeoffs

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Compiler niceties for introspection Out of the box speed for flexibility Maintenance cost for start-up cost Intro • Interface • State • Flow • Tradeoffs

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Interface Out of the box speed for flexibility Maintenance cost for start-up cost Intro • Interface • State • Flow • Tradeoffs

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Interface State Maintenance cost for start-up cost Intro • Interface • State • Flow • Tradeoffs

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Interface State Flow Intro • Interface • State • Flow • Tradeoffs

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Practical Debugging github.com/kddeisz/debugging Kevin Deisz @kddeisz

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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