Deletion Driven Development: Code to delete code! (North American edition)

@chrisarcand Deletion Driven Development: Code to delete code!

Chris Arcand  chrisarcand chrisarcand www.chrisarcand.com

“The Land of 10,000 Lakes”

“The North Star State”

“That super cold place.”

“The Great White South, eh?”

“That one place where those JRuby guys live, right?”

MINNESOTA Minneapolis St. Paul

@chrisarcand chrisarcand.com I PROGRAMMING

@chrisarcand chrisarcand.com I WRITING  CODE

@chrisarcand chrisarcand.com However…

@chrisarcand chrisarcand.com I DELETING  CODE

@chrisarcand chrisarcand.com • Over-engineering  Previous developer adding “potentially helpful” methods
• Poorly written code  Super-speciﬁc, single edge case methods • Refactoring, deprecations  Callers get refactored over time and methods eventually aren’t needed anymore • etc, etc Dead code? How?

@chrisarcand chrisarcand.com “Who cares?”

@chrisarcand chrisarcand.com “Deleting Code” (2002) Ned Batchelder http://nedbatchelder.com/text/deleting-code.html

@chrisarcand chrisarcand.com If you have a chunk of code you
don't need any more, there's one big reason to delete it for real rather than leaving it in a disabled state: To reduce noise and uncertainty. Some of the worst enemies a developer has are noise or uncertainty in his code, because they prevent him from working with it effectively in the future. “

@chrisarcand chrisarcand.com What if we could programmatically ﬁnd unused code
to delete?

@chrisarcand chrisarcand.com Ruby code (.rb) ? ? ?

@chrisarcand chrisarcand.com Part I: Parsing the code

@chrisarcand chrisarcand.com Do you understand the following sequences of characters?
How do you know? Modiﬁed examples and grammar from Robert B. Heckendorn, University of Idaho http://marvin.cs.uidaho.edu/Teaching/CS445/grammar.html

@chrisarcand chrisarcand.com “The boy owns a dog.”

@chrisarcand chrisarcand.com “A boy bites the dog.”

@chrisarcand chrisarcand.com “Loves boy the.”

@chrisarcand chrisarcand.com How could you programmatically determine which of those
are correct… …and which are not?

@chrisarcand chrisarcand.com ✨Context-free Grammar✨  (CFG) A set of production rules
that describe all possible strings in a given formal language. “What sentences are in the language and what are not?”

@chrisarcand chrisarcand.com ✨Backus-Naur Form✨  (BNF) One of two main notation
techniques for context- free grammars, often used to describe computer programming languages.

@chrisarcand chrisarcand.com <sentence> ::= <subject> <predicate> <subject> ::= <article> <noun>
<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES | BITES

<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES | BITES Symbols

<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES | BITES < non-terminals >

<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES | BITES TERMINALS

<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES | BITES Symbol on left is replaced with expression on the right ‘OR’ (choose between expressions) ‘deﬁnitional operator’

<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES | BITES The boy owns a dog.

<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES | BITES The boy owns a dog. <sentence>

<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES | BITES The boy owns a dog. <subject> <predicate>

<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES | BITES The boy owns a dog. <subject> <predicate> <article> <noun>

<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES | BITES The boy owns a dog. <subject> <predicate> <article> <noun> Terminal found

<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES | BITES The boy owns a dog. <subject> <predicate> <article> <noun>

<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES | BITES The boy owns a dog. <subject> <predicate> <article> <noun> Terminal found

<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES | BITES The boy owns a dog. <subject> <predicate> <article> <noun> <verb> <direct-object> <article> <noun>

@chrisarcand chrisarcand.com The boy owns a dog. <subject> <predicate> <article>
<noun> <verb> <direct-object> <article> <noun> <sentence>

@chrisarcand chrisarcand.com <subject> <predicate> <article> <noun> <verb> <direct-object> <article> <noun>
<sentence> THE BOY OWNS A DOG Parsing was successful!

@chrisarcand chrisarcand.com “A boy bites the dog.”

@chrisarcand chrisarcand.com <subject> <predicate> <article> <noun> <verb> <direct-object> <article> <noun>
<sentence> A BOY BITES THE DOG Parsing was successful! …but do boys often bite dogs?

@chrisarcand chrisarcand.com Loves boy the. “ ”

<predicate> ::= <verb> <direct-object> <direct-object> ::= <article> <noun> <article> ::= THE | A <noun> ::= BOY | DOG <verb> ::= OWNS | LOVES Loves boy the. <subject> ??? <article> ??? <noun> ???

@chrisarcand chrisarcand.com “The boy owns a dog.”  “A boy bites
the dog.” “Loves boy the.” In programming terms… OK OK, but perhaps  semantically incorrect  (A bug!) SYNTAX ERROR

@chrisarcand chrisarcand.com How does Ruby know the meaning of these
characters? class Person def initialize(name) @name = name end def say_hello puts “Hi! My name is #{@name}!” end end chris = Person.new(“Chris”) chris.say_hello

@chrisarcand chrisarcand.com Figure 1-13, Ruby Under a Microscope by Pat
Shaughnessy  Used with permission How Ruby tokenizes and parses code

@chrisarcand chrisarcand.com Figure 1-13, Ruby Under a Microscope by Pat
Shaughnessy  Used with permission How Ruby tokenizes and parses code Ruby uses a LALR parser generator called Bison Look-Ahead, Left, Reversed Rightmost Derivation LALR(k): k refers to the amount of look-ahead

@chrisarcand chrisarcand.com Racc https://github.com/tenderlove/racc  An LALR(1) parser generator How we
will tokenize and parse code ruby_parser https://github.com/seattlerb/ruby_parser  A Ruby parser, written in Ruby, using racc

@chrisarcand chrisarcand.com class Person def greet(name) puts "Hello #{name}!" end
end person = Person.new person.greet("RubyConf")

@chrisarcand chrisarcand.com class Person def greet(name) puts "Hello #{name}!" end
end person = Person.new person.greet("RubyConf") > parser = RubyParser.for_current_ruby > parser.parse(File.read(“example1.rb”)) 1 s(:block, 2 s(:class, :Person, nil, 3 s(:defn, :greet, s(:args, :name), 4 s(:call, nil, :puts,   5 s(:dstr, "Hello ", s(:evstr, s(:lvar, :name)), s(:str, "!"))))), 6 s(:lasgn, :person, s(:call, s(:const, :Person), :new)), 7 s(:call, s(:lvar, :person), :greet, s(:str, "RubyConf"))) example1.rb

@chrisarcand chrisarcand.com 1 s(:block, 2 s(:class, :Person, nil, 3 s(:defn,
:greet, s(:args, :name), 4 s(:call, nil, :puts,   5 s(:dstr, "Hello ", s(:evstr, … 6 s(:lasgn, :person, s(:call, … 7 s(:call, s(:lvar, :person), :greet, …

@chrisarcand chrisarcand.com ruby_parser racc Ruby code (.rb) Ruby23Parser Parsing Generic
processing File.read() s-expression (parse tree) ? ? ?

@chrisarcand chrisarcand.com Part II: Processing the s-expression

@chrisarcand chrisarcand.com class MinimalSexpProcessor

@chrisarcand chrisarcand.com def initialize @processors ={} public_methods.each do |name| case
name when /^process_(.*)/ then @processors[$1.to_sym] = name.to_sym end end end end class MinimalSexpProcessor

@chrisarcand chrisarcand.com process_defn

@chrisarcand chrisarcand.com defn =>:process_defn : @processors = { } Node
type Corresponding processor

@chrisarcand chrisarcand.com def process(exp) return nil if exp.nil? type =
exp.first meth = @processors[type] || default_method return nil unless meth if meth == default_method && warn_on_default puts "WARNING: Using default method #{meth} for #{type}" end self.send(meth, exp) if meth end

@chrisarcand chrisarcand.com class MinimalSexpProcessor attr_accessor :default_method attr_accessor :warn_on_default def initialize
@default_method = nil @warn_on_default = true @processors ={} public_methods.each do |name| case name when /^process_(.*)/ then @processors[$1.to_sym] = name.to_sym end end end end def process(exp) return nil if exp.nil? type = exp.first meth = @processors[type] || default_method return nil unless meth if meth == default_method && warn_on_default puts "WARNING: Using default method #{meth} for #{type}" end self.send(meth, exp) if meth end

@chrisarcand chrisarcand.com class MinimalSexpProcessor

@chrisarcand chrisarcand.com class SillyProcessor < MinimalSexpProcessor

@chrisarcand chrisarcand.com def process_defn(exp) method_name = exp[1] puts "PROCESSING A
METHOD DEFINITION NODE: #{method_name}" process_until_empty(exp) s() end def process_not_defn(exp) node_type = exp[0] puts "Processing node: #{node_type}" process_until_empty(exp) s() end

@chrisarcand chrisarcand.com def process_until_empty(exp) until exp.empty? sexp = exp.shift process(sexp)
if Sexp === sexp end end

@chrisarcand chrisarcand.com def initialize super @default_method = :process_not_defn @warn_on_default =
false end

@chrisarcand chrisarcand.com class SillyProcessor < MinimalSexpProcessor def process_defn(exp) method_name =
exp[1] puts "PROCESSING A METHOD DEFINITION NODE: #{method_name}" process_until_empty(exp) s() end def process_not_defn(exp) node_type = exp[0] puts "Processing node: #{node_type}" process_until_empty(exp) s() end def process_until_empty(exp) until exp.empty? sexp = exp.shift process(sexp) if Sexp === sexp end end end def initialize super @default_method = :process_not_defn @warn_on_default = false end

@chrisarcand chrisarcand.com 1 require 'ruby_parser' 2 require_relative 'minimal_sexp_processor.rb' 3 require_relative
'silly_processor.rb' 4 5 parser = RubyParser.for_current_ruby 6 file = File.read(ARGV[0]) 7 sexp = parser.parse(file) 8 9 processor = SillyProcessor.new 10 processor.process(sexp) silly_processor_demo.rb

@chrisarcand chrisarcand.com $ ruby minimal_parser_demo.rb example1.rb Processing node: block Processing
node: class PROCESSING A METHOD DEFINITION NODE: greet Processing node: args Processing node: call Processing node: dstr Processing node: evstr Processing node: lvar Processing node: str Processing node: lasgn Processing node: call Processing node: const Processing node: call Processing node: lvar Processing node: str 1 class Person 2 def greet(name) 3 puts "Hello #{name}!" 4 end 5 end 6 7 person = Person.new 8 person.greet("RubyConf") example1.rb

@chrisarcand chrisarcand.com class MethodTrackingProcessor < MinimalSexpProcessor

@chrisarcand chrisarcand.com attr_reader :method_locations def initialize super @default_method = :process_until_empty
@warn_on_default = false @class_stack = [] @method_stack = [] @method_locations = {} end class MethodTrackingProcessor < MinimalSexpProcessor

@chrisarcand chrisarcand.com def process_defn(exp) exp.shift # node type name =
exp.shift in_method(name, exp.file, exp.line) do process_until_empty(exp) end s() end def process_class(exp) exp.shift # node type in_klass(exp.shift) do process_until_empty(exp) end s() end def process_until_empty(exp) until exp.empty? sexp = exp.shift process(sexp) if Sexp === sexp end end class MethodTrackingProcessor < MinimalSexpProcessor attr_reader :method_locations def initialize super @default_method = :process_until_empty @warn_on_default = false @class_stack = [] @method_stack = [] @method_locations = {} end

@chrisarcand chrisarcand.com def in_method(name, file, line) method_name = Regexp ===
name ? name.inspect : name.to_s @method_stack.unshift(method_name) @method_locations[signature] = "#{file}:#{line}" yield ensure @method_stack.shift end def in_klass(name) @class_stack.unshift(name) with_new_method_stack do yield end ensure @class_stack.shift end def with_new_method_stack old_method_stack, @method_stack = @method_stack, [] yield ensure @method_stack = old_method_stack end class MethodTrackingProcessor < MinimalSexpProcessor attr_reader :method_locations def initialize super @default_method = :process_until_empty @warn_on_default = false @class_stack = [] @method_stack = [] @method_locations = {} end def process_defn(exp) exp.shift # node type name = exp.shift in_method(name, exp.file, exp.line) do process_until_empty(exp) end s() end def process_class(exp) exp.shift # node type in_klass(exp.shift) do process_until_empty(exp) end s() end def process_until_empty(exp) until exp.empty? sexp = exp.shift process(sexp) if Sexp === sexp end end

@chrisarcand chrisarcand.com def klass_name @class_stack.first end def method_name @method_stack.first end
def signature "#{klass_name}##{method_name}" end class MethodTrackingProcessor < MinimalSexpProcessor attr_reader :method_locations def initialize super @default_method = :process_until_empty @warn_on_default = false @class_stack = [] @method_stack = [] @method_locations = {} end def process_defn(exp) exp.shift # node type name = exp.shift in_method(name, exp.file, exp.line) do process_until_empty(exp) end s() end def process_class(exp) exp.shift # node type in_klass(exp.shift) do process_until_empty(exp) end s() end def process_until_empty(exp) until exp.empty? sexp = exp.shift process(sexp) if Sexp === sexp end end def in_method(name, file, line) method_name = Regexp === name ? name.inspect : name.to_s @method_stack.unshift(method_name) @method_locations[signature] = "#{file}:#{line}" yield ensure @method_stack.shift end def in_klass(name) @class_stack.unshift(name) with_new_method_stack do yield end ensure @class_stack.shift end def with_new_method_stack old_method_stack, @method_stack = @method_stack, [] yield ensure @method_stack = old_method_stack end

@chrisarcand chrisarcand.com class MethodTrackingProcessor < MinimalSexpProcessor attr_reader :method_locations def initialize
super @default_method = :process_until_empty @warn_on_default = false @class_stack = [] @method_stack = [] @method_locations = {} end def process_defn(exp) exp.shift # node type name = exp.shift in_method(name, exp.file, exp.line) do process_until_empty(exp) end s() end def process_class(exp) exp.shift # node type in_klass(exp.shift) do process_until_empty(exp) end s() end def process_until_empty(exp) until exp.empty? sexp = exp.shift process(sexp) if Sexp === sexp end end def in_method(name, file, line) method_name = Regexp === name ? name.inspect : name.to_s @method_stack.unshift(method_name) @method_locations[signature] = "#{file}:#{line}" yield ensure @method_stack.shift end def in_klass(name) @class_stack.unshift(name) with_new_method_stack do yield end ensure @class_stack.shift end def with_new_method_stack old_method_stack, @method_stack = @method_stack, [] yield ensure @method_stack = old_method_stack end def klass_name @class_stack.first end def method_name @method_stack.first end def signature "#{klass_name}##{method_name}" end end

@chrisarcand chrisarcand.com 1 class Person 2 def greet(name) 3 puts
"Hello #{name}!" 4 end 5 6 def say_goodbye(name) 7 puts "Goodbye, #{name}!" 8 end 9 end 10 11 class Dog 12 def bark! 13 puts "Woof!" 14 end 15 end 16 17 person = Person.new 18 person.greet("RubyConf") example2.rb

@chrisarcand chrisarcand.com 5 path = ARGV[0] 6 file = File.read(path)
7 sexp = RubyParser.for_current_ruby.process(file, path) 8 9 processor = MethodTrackingProcessor.new 10 processor.process(sexp) 11 pp processor.method_locations method_tracking_demo.rb $ ruby minimal_parser_demo.rb example2.rb { "Person#greet" => "example2.rb:2", "Person#say_goodbye" => "example2.rb:6", “Dog#bark!" => "example2.rb:12" }

@chrisarcand chrisarcand.com ruby_parser racc Ruby code (.rb) Ruby23Parser MethodTrackingProcessor MinimalSexpProcessor
Parsing Generic processing File.read() s-expression (parse tree) Call processing and reporting ? ? ?

@chrisarcand chrisarcand.com Part III: Building the dead method ﬁnder  (or,
drawing the rest of the damn owl)

@chrisarcand chrisarcand.com ruby_parser racc Ruby code (.rb) Ruby23Parser Parsing Generic
processing File.read() s-expression (parse tree) Call processing and reporting Our tool DeadMethodFinder MethodTrackingProcessor MinimalSexpProcessor

@chrisarcand chrisarcand.com class DeadMethodFinder < MethodTrackingProcessor

@chrisarcand chrisarcand.com attr_reader :known attr_reader :called def initialize super @known
= Hash.new { |h,k| h[k] = Set.new } @called = Set.new end class DeadMethodFinder < MethodTrackingProcessor

@chrisarcand chrisarcand.com def process_defn(exp) super do known[plain_method_name] << klass_name process_until_empty(exp)
end end def process_call(exp) method_name = exp[2] called << method_name process_until_empty(exp) exp end attr_reader :known attr_reader :called def initialize super @known = Hash.new { |h,k| h[k] = Set.new } @called = Set.new end class DeadMethodFinder < MethodTrackingProcessor

@chrisarcand chrisarcand.com def uncalled not_called = known.keys - called.to_a by_class
= Hash.new { |h,k| h[k] = [] } not_called.each do |meth| known[meth].each do |klass| by_class[klass] << meth end end by_class end # #method_name -> :method_name def plain_method_name method_name.to_s.sub(/^::|#/, "").to_sym end attr_reader :known attr_reader :called def initialize super @known = Hash.new { |h,k| h[k] = Set.new } @called = Set.new end def process_defn(exp) super do known[plain_method_name] << klass_name process_until_empty(exp) end end def process_call(exp) method_name = exp[2] called << method_name process_until_empty(exp) exp end class DeadMethodFinder < MethodTrackingProcessor

@chrisarcand chrisarcand.com attr_reader :known attr_reader :called def initialize super @known
= Hash.new { |h,k| h[k] = Set.new } @called = Set.new end def process_defn(exp) super do known[plain_method_name] << klass_name process_until_empty(exp) end end def process_call(exp) method_name = exp[2] called << method_name process_until_empty(exp) exp end def uncalled not_called = known.keys - called.to_a by_class = Hash.new { |h,k| h[k] = [] } not_called.each do |meth| known[meth].each do |klass| by_class[klass] << meth end end by_class end # #method_name -> :method_name def plain_method_name method_name.to_s.sub(/^::|#/, "").to_sym end end class DeadMethodFinder < MethodTrackingProcessor

@chrisarcand chrisarcand.com 1 class Person 2 def greet(name) 3 speak
"Hello #{name}!" 4 end 5 6 # Never used 7 def say_goodbye(name) 8 speak "Goodbye, #{name}!" 9 end 10 11 def speak(text) 12 puts text 13 end 14 15 def pet_dog(dog) 16 dog.send(:pet) 17 end 18 end 19 20 class Dog 21 attr_accessor :fed # Never used 22 23 def bark! 24 puts "Bark!" 25 end 26 27 def pet 28 puts "Ahhh..." 29 end 30 end 31 32 33 chris = Person.new 34 reuben = Dog.new 35 36 chris.greet("RubyConf") 37 reuben.bark! 38 chris.pet_dog(reuben) example3.rb => Hello RubyConf!  Bark!   Ahhh…

"Hello #{name}!" 4 end 5 6 # Never used 7 def say_goodbye(name) 8 speak "Goodbye, #{name}!" 9 end 10 11 def speak(text) 12 puts text 13 end 14 15 def pet_dog(dog) 16 dog.send(:pet) 17 end 18 end 19 20 class Dog 21 attr_accessor :fed # Never used 22 23 def bark! 24 puts "Bark!" 25 end 26 27 def pet 28 puts "Ahhh..." 29 end 30 end 31 32 33 chris = Person.new 34 reuben = Dog.new 35 36 chris.greet("RubyConf") 37 reuben.bark! 38 chris.pet_dog(reuben) example3.rb > processor = DeadMethodFinder.new > processor.process(sexp) > puts processor.uncalled => {"Person"=>[:say_goodbye], "Dog"=>[:pet]}

@chrisarcand chrisarcand.com s(:call, s(:lvar, :dog), :send, s(:lit, :pet)) dog.send(:pet)

@chrisarcand chrisarcand.com def process_call(exp) method_name = exp[2] case method_name when
:send, :public_send, :__send__ msg_arg = exp[3] if Sexp === msg_arg && [:lit, :str].include?(msg_arg.sexp_type) called << msg_arg.last.to_sym end end called << method_name process_until_empty(exp) exp end s(:call, s(:lvar, :dog), :send, s(:lit, :pet)) 0 1 2 3

"Hello #{name}!" 4 end 5 6 # Never used 7 def say_goodbye(name) 8 speak "Goodbye, #{name}!" 9 end 10 11 def speak(text) 12 puts text 13 end 14 15 def pet_dog(dog) 16 dog.send(:pet) 17 end 18 end 19 20 class Dog 21 attr_accessor :fed # Never used 22 23 def bark! 24 puts "Bark!" 25 end 26 27 def pet 28 puts "Ahhh..." 29 end 30 end 31 32 33 chris = Person.new 34 reuben = Dog.new 35 36 chris.greet("RubyConf") 37 reuben.bark! 38 chris.pet_dog(reuben) example3.rb > processor = DeadMethodFinder.new > processor.process(sexp) > puts processor.uncalled => {"Person"=>[:say_goodbye]}

@chrisarcand chrisarcand.com s(:call, nil, :attr_accessor, s(:lit, :fed)) attr_accessor :fed

@chrisarcand chrisarcand.com s(:call, nil, :attr_accessor, s(:lit, :fed)) def process_call(exp) method_name
= exp[2] case method_name when :attr_accessor _, _, _, *args = exp file, line = exp.file, exp.line args.each do |(_, name)| record_known_method(name, file, line) record_known_method("#{name}=".to_sym, file, line) end when :send, :public_send, :__send__ _, _, _, msg_arg, * = exp if Sexp === msg_arg && [:lit, :str].include?(msg_arg.sexp_type) called << msg_arg.last.to_sym end end called << method_name process_until_empty(exp) exp end def record_known_method(name, file, line) signature = "#{klass_name}##{name}" method_locations[signature] = "#{file}:#{line}" known[name] << klass_name end 0 1 2 3

@chrisarcand chrisarcand.com def report puts "These methods MIGHT not be
called:" uncalled.each do |klass, methods| not_called_methods = methods.map do |method| location = method_locations["#{klass}##{method}"] " %-35s %s" % [method, location] end not_called_methods.compact! next if not_called_methods.empty? puts "\n#{klass}" puts not_called_methods.join "\n" end end

@chrisarcand chrisarcand.com > processor = DeadMethodFinder.new > processor.process(sexp)  > processor.report

"Hello #{name}!" 4 end 5 6 # Never used 7 def say_goodbye(name) 8 speak "Goodbye, #{name}!" 9 end 10 11 def speak(text) 12 puts text 13 end 14 15 def pet_dog(dog) 16 dog.send(:pet) 17 end 18 end 19 20 class Dog 21 attr_accessor :fed # Never used 22 23 def bark! 24 puts "Bark!" 25 end 26 27 def pet 28 puts "Ahhh..." 29 end 30 end 31 32 33 chris = Person.new 34 reuben = Dog.new 35 36 chris.greet("RubyConf") 37 reuben.bark! 38 chris.pet_dog(reuben) example2.rb These methods MIGHT not be called:    Person say_goodbye example2.rb:7 Dog fed example2.rb:21 fed= example2.rb:21

"Hello #{name}!" 4 end 5 6 7 8 9 10 11 def speak(text) 12 puts text 13 end 14 15 def pet_dog(dog) 16 dog.send(:pet) 17 end 18 end 19 20 class Dog 21 22 23 def bark! 24 puts "Bark!" 25 end 26 27 def pet 28 puts "Ahhh..." 29 end 30 end 31 32 33 chris = Person.new 34 reuben = Dog.new 35 36 chris.greet("RubyConf") 37 reuben.bark! 38 chris.pet_dog(reuben) # Never used def say_goodbye(name) speak "Goodbye, #{name}!" end attr_accessor :fed # Never used - - - - - example2.rb

@chrisarcand chrisarcand.com ✌ Done?

@chrisarcand chrisarcand.com Done Ruby is complex (to parse)

@chrisarcand chrisarcand.com Done? Ruby is complex (to parse) …but adding
edge cases is easy.

@chrisarcand chrisarcand.com reuben.fed = true

"Hello #{name}!" 4 end 5 6 # Never used 7 def say_goodbye(name) 8 speak "Goodbye, #{name}!" 9 end 10 11 def speak(text) 12 puts text 13 end 14 15 def pet_dog(dog) 16 dog.send(:pet) 17 end 18 end 19 20 class Dog 21 attr_accessor :fed # Never used 22 23 def bark! 24 puts "Bark!" 25 end 26 27 def pet 28 puts "Ahhh..." 29 end 30 end 31 32 33 chris = Person.new 34 reuben = Dog.new 35 36 chris.greet("RubyConf") 37 reuben.bark! 38 chris.pet_dog(reuben)  39 example4.rb Person say_goodbye example2.rb:7 Dog fed example2.rb:21 fed= example2.rb:21 reuben.fed = true

Brought to you by: Julian Cheal

@chrisarcand chrisarcand.com s(:attrasgn, s(:lvar, :reuben), :fed=, s(:true)) def process_attrasgn(exp) method_name
= exp[2] method_name = method_name.last if Sexp === method_name called << method_name process_until_empty exp exp end reuben.fed = true

"Hello #{name}!" 4 end 5 6 # Never used 7 def say_goodbye(name) 8 speak "Goodbye, #{name}!" 9 end 10 11 def speak(text) 12 puts text 13 end 14 15 def pet_dog(dog) 16 dog.send(:pet) 17 end 18 end 19 20 class Dog 21 attr_accessor :fed # Never used 22 23 def bark! 24 puts "Bark!" 25 end 26 27 def pet 28 puts "Ahhh..." 29 end 30 end 31 32 33 chris = Person.new 34 reuben = Dog.new 35 36 chris.greet("RubyConf") 37 reuben.bark! 38 chris.pet_dog(reuben)  39 reuben.fed = true example4.rb Person say_goodbye example2.rb:7 Dog fed example2.rb:21

@chrisarcand chrisarcand.com What about Rails DSL?

@chrisarcand chrisarcand.com :after_commit :before_create :after_create :before_destroy :before_filter :before_action :after_validation :before_update
:around_save :validates :validates_length_of :validates_format_of :validates_cuteness_of :validates_confirmation_of :validate

@chrisarcand chrisarcand.com What about my own DSL?

@chrisarcand chrisarcand.com

@chrisarcand chrisarcand.com class Disk < ActiveRecord::Base has_many :partitions virtual_column :allocated_space,
type: :integer, uses: :partitions virtual_column :used_percent_of_provisioned, type: :float virtual_has_many :storage_systems, class_name: "CimComputerSystem" def allocated_space # ... end def used_percent_of_provisioned # ... end end

@chrisarcand chrisarcand.com RAILS_DSL_METHODS = [ :after_action, :around_action, :before_action, ...  ...
] def process_call(exp) # ... when *RAILS_DSL_METHODS + AR_VIRTUAL_DSL_METHODS _, _, _, (_, new_name), possible_hash = exp called << new_name if Sexp === possible_hash && possible_hash.sexp_type == :hash possible_hash.sexp_body.each_slice(2) do |key, val| next unless Sexp === val called << val.last if val.first == :lit called << val.last.to_sym if val.first == :str end end # ... end

@chrisarcand chrisarcand.com As with most things, with the right tools,
the job isn’t very difﬁcult. Customization is easy.

@chrisarcand chrisarcand.com Other things that are easy: Executing this code
on your project, right now.

@chrisarcand chrisarcand.com debride https://github.com/seattlerb/debride debride (v): To remove dead, contaminated,
or adherent tissue and/or foreign material.

@chrisarcand chrisarcand.com ruby_parser racc Ruby code (.rb) Ruby23Parser Parsing File.read()

@chrisarcand chrisarcand.com ruby_parser racc sexp_processor Ruby code (.rb) Ruby23Parser MethodBasedSexpProcessor
SexpProcessor Parsing Generic processing File.read() s-expression (parse tree)

@chrisarcand chrisarcand.com ruby_parser racc sexp_processor Ruby code (.rb) Ruby23Parser MethodBasedSexpProcessor
SexpProcessor Parsing Generic processing File.read() s-expression (parse tree) Call processing and reporting debride Debride

@chrisarcand chrisarcand.com $ debride [options] files_or_dirs -e, --exclude FILE1,FILE2,ETC -w,
--whitelist PATTERN -f, --focus PATH -r, --rails -v, --verbose

@chrisarcand chrisarcand.com - @called = Set.new + @called = Hash.new
{ |h,k| h[k] = 0 } - called << method_name + called[method_name] += 1 - not_called = known.keys - called.to_a + called_once = called.select { |_, v| v == 1 } API Quality Control - Single call methods

@chrisarcand chrisarcand.com Future considerations: • Pushing more work upstream ✴
Bug ﬁxes ✴ Cleanup ✴ Potential features

@chrisarcand chrisarcand.com But wait, there’s more! Unused by Josh Clayton 
https://github.com/joshuaclayton/unused  Written in Haskell, this project utilizes ctags to statically ﬁnd unused code OldeCodeFinder by Tom Copeland  https://github.com/tcopeland/olde_code_ﬁnder  A Ruby gem checking code content by date and authorship Here’s a few…

@chrisarcand chrisarcand.com No code is faster than no code. No
code has fewer bugs than no code. No code is easier to understand than no code. No code is more maintainable than no code.

Thank you!  Questions? chrisarcand chrisarcand www.chrisarcand.com

Deletion Driven Development: Code to delete cod...

Deletion Driven Development: Code to delete code! (North American edition)

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