Nothing is Something (RailsConf)

Jan 2015 @sandimetz Sandi Metz Nothing is Something

Jan 2015 @sandimetz

Jan 2015 @sandimetz Smalltalk Infected

Jan 2015 @sandimetz 1.to_s

Jan 2015 @sandimetz 1.to_s => "1"

Jan 2015 @sandimetz 1.to_s => "1" 1.send(:to_s)

=> "1"

=> "1" 1 + 1

=> "1" 1 + 1 => 2

=> "1" 1 + 1 => 2 1.send(:+, 1)

=> "1" 1 + 1 => 2 1.send(:+, 1) => 2

Jan 2015 @sandimetz 1.class 1.to_s => "1" 1.send(:to_s)
=> "1" 1 + 1 => 2 1.send(:+, 1) => 2

Jan 2015 @sandimetz 1.class => Fixnum 1.to_s =>
"1" 1.send(:to_s) => "1" 1 + 1 => 2 1.send(:+, 1) => 2

Jan 2015 @sandimetz Fixnum.instance_methods(false) => [ :to_s,
:+, :-‐, :*, :/, :==, :%, :modulo, # etc 1.to_s => "1" 1.send(:to_s) => "1" 1 + 1 => 2 1.send(:+, 1) => 2

=> "1" 1 + 1 => 2 1.send(:+, 1) => 2 1 == 1

=> "1" 1 + 1 => 2 1.send(:+, 1) => 2 1 == 1 => true

=> "1" 1 + 1 => 2 1.send(:+, 1) => 2 1 == 1 => true true.class

=> "1" 1 + 1 => 2 1.send(:+, 1) => 2 1 == 1 => true true.class => TrueClass

=> "1" 1 + 1 => 2 1.send(:+, 1) => 2 1 == 1 => true true.class => TrueClass TrueClass.instance_methods(false) => [ :to_s, :inspect, :&, :|, :^, :pretty_print_cycle, :pretty_print]

Jan 2015 @sandimetz ‘Special’ syntax for booleans

Jan 2015 @sandimetz Smalltalk keywords true, false, nil, self, super,
thisContext

Jan 2015 @sandimetz Smalltalk keywords true, false, nil, self, super,
thisContext Ruby keywords alias and BEGIN begin break case class def defined? do else elsif END end ensure false for if in module next nil not or redo rescue retry return self super then true undef unless until when while yield

Jan 2015 @sandimetz if (1 == 1) 'is
true' else 'is false' end

true' else 'is false' end true

true' else 'is false' end => 'is true' true

Jan 2015 @sandimetz if (1 == 1) code
to eval when ‘true’ else code to eval when ‘false’ end true

Jan 2015 @sandimetz if ( truthy ) code
to eval when ‘truthy’ else code to eval when ‘falsey’ end

Jan 2015 @sandimetz if (some object whose type I know)
code to do some stuff else code to do some other stuff end

Jan 2015 @sandimetz I just want to send a message
to an object

Jan 2015 @sandimetz

Jan 2015 @sandimetz if

Jan 2015 @sandimetz if is an enabler

Jan 2015 @sandimetz ‘Message sending’ syntax for TrueClass / FalseClass

Jan 2015 @sandimetz class TrueClass end

Jan 2015 @sandimetz class TrueClass def if_true
yield end end

yield self end end

yield self end def if_false self end end

yield self end def if_false self end end class FalseClass def if_true self end def if_false yield self end end

Jan 2015 @sandimetz (1 == 1).if_true {puts "evaluated block"}

Jan 2015 @sandimetz (1 == 1).if_true {puts "evaluated block"} true

Jan 2015 @sandimetz (1 == 1).if_true {puts "evaluated block"} class
TrueClass def if_true yield self end # … end true

Jan 2015 @sandimetz (1 == 1).if_true {puts "evaluated block"} class
TrueClass def if_true yield self end # … end

"evaluated block" class TrueClass def if_true yield self end # … end

"evaluated block" (1 == 1).if_false {puts "evaluated block"} class TrueClass def if_true yield self end # … end

"evaluated block" (1 == 1).if_false {puts "evaluated block"} class TrueClass def if_true yield self end def if_false self end end

"evaluated block" (1 == 1).if_false {puts "evaluated block"} # block is ignored class TrueClass def if_true yield self end def if_false self end end

"evaluated block" (1 == 1).if_false {puts "evaluated block"} # block is ignored (1 == 2).if_true {puts "evaluated block"}

"evaluated block" (1 == 1).if_false {puts "evaluated block"} # block is ignored (1 == 2).if_true {puts "evaluated block"} false

"evaluated block" (1 == 1).if_false {puts "evaluated block"} # block is ignored (1 == 2).if_true {puts "evaluated block"} false class FalseClass def if_true self end def if_false yield self end end

"evaluated block" (1 == 1).if_false {puts "evaluated block"} # block is ignored (1 == 2).if_true {puts "evaluated block"} class FalseClass def if_true self end def if_false yield self end end

"evaluated block" (1 == 1).if_false {puts "evaluated block"} # block is ignored (1 == 2).if_true {puts "evaluated block"} # block is ignored class FalseClass def if_true self end def if_false yield self end end

"evaluated block" (1 == 1).if_false {puts "evaluated block"} # block is ignored (1 == 2).if_true {puts "evaluated block"} # block is ignored (1 == 2).if_false {puts "evaluated block"} class FalseClass def if_true self end def if_false yield self end end

"evaluated block" (1 == 1).if_false {puts "evaluated block"} # block is ignored (1 == 2).if_true {puts "evaluated block"} # block is ignored (1 == 2).if_false {puts "evaluated block"} "evaluated block" class FalseClass def if_true self end def if_false yield self end end

Jan 2015 @sandimetz ‘Message sending’ syntax for truthy/falsey

Jan 2015 @sandimetz class Object def if_true

yield self end def if_false self end end class FalseClass def if_true self end def if_false yield self end end class NilClass def if_true self end def if_false yield self end end

yield self end def if_false self end end class FalseClass def if_true self end def if_false yield self end end class NilClass def if_true self end def if_false yield self end end * Shamelessly swiped from http://yehudakatz.com/2009/10/04/emulating-smalltalks-conditionals-in-ruby/

Jan 2015 @sandimetz (1 == 1).if_true {puts "evaluated
block"}

Jan 2015 @sandimetz

Jan 2015 @sandimetz "anything".if_true {puts "evaluated block"}

Jan 2015 @sandimetz "anything".if_true {puts "evaluated block"} "evaluated block"

Jan 2015 @sandimetz "anything".if_true {puts "evaluated block"} "evaluated
block" "anything".if_false {puts "evaluated block"}

block" "anything".if_false {puts "evaluated block"} # block is ignored

block" "anything".if_false {puts "evaluated block"} # block is ignored nil.if_true {puts "evaluated block"}

block" "anything".if_false {puts "evaluated block"} # block is ignored nil.if_true {puts "evaluated block"} # block is ignored

block" "anything".if_false {puts "evaluated block"} # block is ignored nil.if_true {puts "evaluated block"} # block is ignored nil.if_false {puts "evaluated block"}

block" "anything".if_false {puts "evaluated block"} # block is ignored nil.if_true {puts "evaluated block"} # block is ignored nil.if_false {puts "evaluated block"} "evaluated block"

Jan 2015 @sandimetz if (1 == 1) puts
'is true' else puts 'is false' end => 'is true'

Jan 2015 @sandimetz (1 == 1). if_true {puts
'is true'}. if_false {puts 'is false’} => 'is true' if (1 == 1) puts 'is true' else puts 'is false' end => 'is true'

'is true' else puts 'is false' end => 'is false' (1 == 1). if_true {puts 'is true'}. if_false {puts 'is false’} => 'is true' if (1 == 1) puts 'is true' else puts 'is false' end => 'is true'

'is true' else puts 'is false' end => 'is false' (1 == 1). if_true {puts 'is true'}. if_false {puts 'is false’} => 'is true' if (1 == 1) puts 'is true' else puts 'is false' end => 'is true' (1 == 2). if_true {puts 'is true'}. if_false {puts 'is false’} => 'is false'

Jan 2015 @sandimetz I don't want to change Ruby

Jan 2015 @sandimetz I want to change you

Jan 2015 @sandimetz What if there were no 'if' ?

Jan 2015 @sandimetz Smalltalk Infected

Jan 2015 @sandimetz Smalltalk Infected Condition Averse

Jan 2015 @sandimetz Animal.find('pig') => #<Animal:0x007f94b28b0030 @name="pig">

Jan 2015 @sandimetz Animal.find('pig') => #<Animal:0x007f94b28b0030 @name="pig"> Animal.find('')
=> nil

Jan 2015 @sandimetz ids = ['pig', '', 'sheep']

Jan 2015 @sandimetz ids = ['pig', '', 'sheep'] animals
= ids.map {|id| Animal.find(id)}

= ids.map {|id| Animal.find(id)} => [#<Animal:0x007f94b290ae90 @name="pig">, nil, #<Animal:0x007f94b290ae18 @name="sheep">]

= ids.map {|id| Animal.find(id)} => [#<Animal:0x007f94b290ae90 @name="pig">, nil, #<Animal:0x007f94b290ae18 @name="sheep">] animals.each {|animal| puts animal.name} => 'pig' NoMethodError: undefined method `name' for nil:NilClass

Jan 2015 @sandimetz Sometimes nil is nothing

= ids.map {|id| Animal.find(id)} => [#<Animal: @name="pig">, nil, #<Animal: @name="sheep">]

= ids.map {|id| Animal.find(id)} => [#<Animal: @name="pig">, nil, #<Animal: @name="sheep">] animals.compact => [#<Animal: @name="pig">, #<Animal: @name="sheep">]

= ids.map {|id| Animal.find(id)} => [#<Animal: @name="pig">, nil, #<Animal: @name="sheep">] animals.compact => [#<Animal: @name="pig">, #<Animal: @name="sheep">] animals.each {|animal|puts animal.name} => 'pig' 'sheep'

Jan 2015 @sandimetz

Jan 2015 @sandimetz But if you send it a message

Jan 2015 @sandimetz But if you send it a message
nil is something

= ids.map {|id| Animal.find(id)} => [#<Animal:0x007f94b290ae90 @name="pig">, nil, #<Animal:0x007f94b290ae18 @name="sheep">] animals.each {|animal| puts animal.name} => 'pig' NoMethodError: undefined method `name' for nil:NilClass

= ids.map {|id| Animal.find(id)} => [#<Animal:0x007f94b290ae90 @name="pig">, nil, #<Animal:0x007f94b290ae18 @name="sheep">] animals.each {|animal| puts animal.nil? ? 'no animal' : animal.name} => 'pig' 'no animal' 'sheep'

= ids.map {|id| Animal.find(id)} => [#<Animal:0x007f94b290ae90 @name="pig">, nil, #<Animal:0x007f94b290ae18 @name="sheep">] animals.each {|animal| puts animal && animal.name } => 'pig' empty string 'sheep'

= ids.map {|id| Animal.find(id)} => [#<Animal:0x007f94b290ae90 @name="pig">, nil, #<Animal:0x007f94b290ae18 @name="sheep">] animals.each {|animal| puts animal.try(:name)} => 'pig' empty string 'sheep'

Jan 2015 @sandimetz puts animal.try(:name) puts animal.nil? ? ''
: animal.name puts animal == nil ? '' : animal.name puts animal.is_a?(NilClass) ? '' : animal.name

Jan 2015 @sandimetz puts animal.is_a?(NilClass) ? '' : animal.name
if animal.is_a?(NilClass) puts '' else puts animal.name end

Jan 2015 @sandimetz if animal.is_a?(NilClass) puts ''
else puts animal.name end

code to do some stuff else code to do some other stuff end if animal.is_a?(NilClass) puts 'no animal' else puts animal.name end

I'll supply the behavior else code to do some other stuff end if animal.is_a?(NilClass) puts 'no animal' else puts animal.name end

Jan 2015 @sandimetz if animal.is_a?(NilClass) puts 'no animal'
else puts animal.name end if (some object whose type I know) I'll supply the behavior else I'll send a message end

Jan 2015 @sandimetz

Jan 2015 @sandimetz conditions

Jan 2015 @sandimetz conditions breed

Jan 2015 @sandimetz class Animal def self.find animal =
Animal.find(id) animal.nil? ? 'no animal' : animal.name

Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name

Jan 2015 @sandimetz class Animal def self.find ind(id)
'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name Animal.find(id) ? 'no animal' : animal.name

'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name Animal.find(id) ? 'no animal' : animal.name find(id) animal' : animal.name d) imal' : animal.name

'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name Animal.find(id) ? 'no animal' : animal.name find(id) animal' : animal.name d) imal' : animal.name 'no animal'

'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name Animal.find(id) ? 'no animal' : animal.name find(id) animal' : animal.name d) imal' : animal.name 'no animal' 'no animal'

'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name Animal.find(id) ? 'no animal' : animal.name find(id) animal' : animal.name d) imal' : animal.name 'no animal' 'no animal' 'no animal'

'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name Animal.find(id) ? 'no animal' : animal.name find(id) animal' : animal.name d) imal' : animal.name 'no animal' 'no animal' 'no animal' 'no animal'

'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name animal = Animal.find(id) animal.nil? ? 'no animal' : animal.name Animal.find(id) ? 'no animal' : animal.name find(id) animal' : animal.name d) imal' : animal.name 'no animal' 'no animal' 'no animal' 'no animal' 'no animal' !!!!

Jan 2015 @sandimetz Change?

Jan 2015 @sandimetz Shotgun Surgery

Jan 2015 @sandimetz Smalltalk Infected Condition Averse

Jan 2015 @sandimetz Smalltalk Infected Condition Averse Message Centric

else puts animal.name end if (some object whose type I know) I'll supply the behavior else I'll send a message end

else puts animal.name end

Jan 2015 @sandimetz class Animal def name
... end end

... end end class Nil # does not understand name end

... end end class ??? def name 'no animal' end end

... end end class MissingAnimal def name 'no animal' end end

Jan 2015 @sandimetz Prefer knowing an object to duplicating behavior

= ids.map {|id| Animal.find(id)} => [#<Animal: @name="pig">, nil, #<Animal: @name="sheep">] animals.each {|animal| if animal.is_a?(NilClass) puts 'no animal' else puts animal.name end }

= ids.map {|id| Animal.find(id) || MissingAnimal.new} => [#<Animal: @name="pig">, nil, #<Animal: @name="sheep">] animals.each {|animal| if animal.is_a?(NilClass) puts 'no animal' else puts animal.name end }

= ids.map {|id| Animal.find(id) || MissingAnimal.new} => [#<Animal: @name="pig">, #<MissingAnimal:>, #<Animal: @name="sheep">] animals.each {|animal| if animal.is_a?(NilClass) puts 'no animal' else puts animal.name end }

= ids.map {|id| Animal.find(id) || MissingAnimal.new} => [#<Animal: @name="pig">, #<MissingAnimal:>, #<Animal: @name="sheep">] animals.each {|animal| if animal.is_a?(NilClass) puts 'no animal' else puts animal.name end } added dependency

= ids.map {|id| Animal.find(id) || MissingAnimal.new} => [#<Animal: @name="pig">, #<MissingAnimal:>, #<Animal: @name="sheep">] animals.each {|animal| if animal.is_a?(NilClass) puts 'no animal' else puts animal.name end } still have the condition

= ids.map {|id| Animal.find(id) || MissingAnimal.new} => [#<Animal: @name="pig">, #<MissingAnimal:>, #<Animal: @name="sheep">] animals.each {|animal| if animal.is_a?(NilClass) puts 'no animal' else puts animal.name end } but no longer own the behavior

= ids.map {|id| Animal.find(id) || MissingAnimal.new} => [#<Animal: @name="pig">, #<MissingAnimal:>, #<Animal: @name="sheep">] animals.each {|animal| puts animal.name }

= ids.map {|id| Animal.find(id) || MissingAnimal.new} => [#<Animal: @name="pig">, #<MissingAnimal:>, #<Animal: @name="sheep">] animals.each {|animal| puts animal.name}

= ids.map {|id| Animal.find(id) || MissingAnimal.new} => [#<Animal: @name="pig">, #<MissingAnimal:>, #<Animal: @name="sheep">] animals.each {|animal| puts animal.name} => 'pig' 'no animal' 'sheep'

... end end class MissingAnimal def name 'no animal' end end

Jan 2015 @sandimetz

Jan 2015 @sandimetz Null Object Pattern

Jan 2015 @sandimetz Null Object Pattern 'Active Nothing'

= ids.map {|id| Animal.find(id) || MissingAnimal.new} animals.each {|animal| puts animal.name} => 'pig' 'no animal' 'sheep'

= ids.map {|id| Animal.find(id) || MissingAnimal.new} animals.each {|animal| puts animal.name} => 'pig' 'no animal' 'sheep' dependency

Jan 2015 @sandimetz Prefer knowing an object to duplicating behavior

Jan 2015 @sandimetz Prefer knowing few objects

Animal.find(id) || MissingAnimal.new animal.name

Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name

Jan 2015 @sandimetz class Animal def self.find || MissingAnimal.new
animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name al.find(id) || MissingAnimal.new

animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name al.find(id) || MissingAnimal.new ) || MissingAnimal.new issingAnimal.new

animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name al.find(id) || MissingAnimal.new ) || MissingAnimal.new issingAnimal.new MissingAnimal

animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name al.find(id) || MissingAnimal.new ) || MissingAnimal.new issingAnimal.new MissingAnimal MissingAnimal

animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name al.find(id) || MissingAnimal.new ) || MissingAnimal.new issingAnimal.new MissingAnimal MissingAnimal MissingAnimal

animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name al.find(id) || MissingAnimal.new ) || MissingAnimal.new issingAnimal.new MissingAnimal MissingAnimal MissingAnimal MissingAnimal

animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name animal = Animal.find(id) || MissingAnimal.new animal.name al.find(id) || MissingAnimal.new ) || MissingAnimal.new issingAnimal.new MissingAnimal MissingAnimal MissingAnimal MissingAnimal MissingAnimal ???

Jan 2015 @sandimetz class Animal def self.find(id)
# nil or an Animal end # … end

Jan 2015 @sandimetz class Animal def self.find

Jan 2015 @sandimetz class GuaranteedAnimal def self.find class Animal
def self.find

Jan 2015 @sandimetz class GuaranteedAnimal def self.find class Animal
def self.find class GuaranteedAnimal def self.find(id) Animal.find(id) || MissingAnimal.new end end

Jan 2015 @sandimetz animals = ids.map {|id|Animal.find(id)||MissingAnimal.new}

Jan 2015 @sandimetz animals = ids.map {|id| GuaranteedAnimal.find(id)}
=> [#<Animal: @name="pig">, #<MissingAnimal:>, #<Animal: @name="sheep">]

Jan 2015 @sandimetz animals = ids.map {|id| GuaranteedAnimal.find(id)}
=> [#<Animal: @name="pig">, #<MissingAnimal:>, #<Animal: @name="sheep">] animals.each {|animal| puts animal.name } => 'pig' 'no animal' 'sheep'

Jan 2015 @sandimetz Smalltalk Infected Condition Averse Message Centric

Jan 2015 @sandimetz Smalltalk Infected Condition Averse Message Centric Abstraction
Seeking

Jan 2015 @sandimetz 'This is the house that Jack
built.' 1

built.' 'This is the malt that lay in the house that Jack built.' 1 2

built.' 'This is the malt that lay in the house that Jack built.' 'This is the rat that ate the malt that lay in the house that Jack built.' 1 2 3

built.' 'This is the malt that lay in the house that Jack built.' 'This is the rat that ate the malt that lay in the house that Jack built.' 'This is the horse and the hound and the horn that belonged to the farmer sowing his corn that kept the rooster that crowed in the morn that woke the priest all shaven and shorn that married the man all tattered and torn that kissed the maiden all forlorn that milked the cow with the crumpled horn that tossed the dog that worried the cat that killed the rat that ate the malt that lay in the house that Jack built.' 12

Jan 2015 @sandimetz [ 'the horse and
the hound and the horn that belonged to', 'the farmer sowing his corn that kept', 'the rooster that crowed in the morn that woke', 'the priest all shaven and shorn that married', 'the man all tattered and torn that kissed', 'the maiden all forlorn that milked', 'the cow with the crumpled horn that tossed', 'the dog that worried', 'the cat that killed', 'the rat that ate', 'the malt that lay in', 'the house that Jack built' ]

Jan 2015 @sandimetz def data
[ 'the horse and the hound and the horn that belonged to', 'the farmer sowing his corn that kept', 'the rooster that crowed in the morn that woke', 'the priest all shaven and shorn that married', 'the man all tattered and torn that kissed', 'the maiden all forlorn that milked', 'the cow with the crumpled horn that tossed', 'the dog that worried', 'the cat that killed', 'the rat that ate', 'the malt that lay in', 'the house that Jack built'] end

Jan 2015 @sandimetz def phrase(number)
data.last(number).join(" ") end def data [ 'the horse and the hound and the horn that belonged to', 'the farmer sowing his corn that kept', 'the rooster that crowed in the morn that woke', 'the priest all shaven and shorn that married', 'the man all tattered and torn that kissed', 'the maiden all forlorn that milked', 'the cow with the crumpled horn that tossed', 'the dog that worried', 'the cat that killed', 'the rat that ate', 'the malt that lay in', 'the house that Jack built'] end

data.last(number).join(" ") end def data [ 'the horse and the hound and the horn that belonged to', 'the farmer sowing his corn that kept', 'the rooster that crowed in the morn that woke', 'the priest all shaven and shorn that married', 'the man all tattered and torn that kissed', 'the maiden all forlorn that milked', 'the cow with the crumpled horn that tossed', 'the dog that worried', 'the cat that killed', 'the rat that ate', 'the malt that lay in', 'the house that Jack built'] end data.last(3) => ['the rat that ate', 'the malt that lay in', 'the house that Jack built']

data.last(number).join(" ") end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end

Jan 2015 @sandimetz def line(number)
"This is #{phrase(number)}.\n" end def phrase(number) data.last(number).join(" ") end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end

Jan 2015 @sandimetz def recite
(1..data.length).map {|i| line(i)}.join("\n") end def line(number) "This is #{phrase(number)}.\n" end def phrase(number) data.last(number).join(" ") end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end

Jan 2015 @sandimetz class House def recite
(1..data.length).map {|i| line(i)}.join("\n") end def line(number) "This is #{phrase(number)}.\n" end def phrase(number) data.last(number).join(" ") end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end

Jan 2015 @sandimetz

Jan 2015 @sandimetz puts House.new.line(1) => 'This is the house
that Jack built.'

that Jack built.' puts House.new.line(2) => 'This is the malt that lay in the house that Jack built.'

that Jack built.' puts House.new.line(2) => 'This is the malt that lay in the house that Jack built.' puts House.new.line(3) => 'This is the rat that ate the malt that lay in the house that Jack built.'

that Jack built.' puts House.new.line(2) => 'This is the malt that lay in the house that Jack built.' puts House.new.line(3) => 'This is the rat that ate the malt that lay in the house that Jack built.' puts House.new.line(12) => 'This is the horse and the hound and the horn that belonged to the farmer sowing his corn that kept the rooster that crowed in the morn that woke the priest all shaven and shorn that married the man all tattered and torn that kissed the maiden all forlorn that milked the cow with the crumpled horn that tossed the dog that worried the cat that killed the rat that ate the malt that lay in the house that Jack built.'

that Jack built.' puts House.new.line(2) => 'This is the malt that lay in the house that Jack built.' puts House.new.line(3) => 'This is the rat that ate the malt that lay in the house that Jack built.' puts House.new.line(12) => 'This is the horse and the hound and the horn that belonged to the farmer sowing his corn that kept the rooster that crowed in the morn that woke the priest all shaven and shorn that married the man all tattered and torn that kissed the maiden all forlorn that milked the cow with the crumpled horn that tossed the dog that worried the cat that killed the rat that ate the malt that lay in the house that Jack built.' puts House.new.recite => 'This is the house that Jack built.' 'This is the malt that lay in the house that Jack built.' 'This is the rat that ate the malt that lay in the house that Jack built.' etc

Jan 2015 @sandimetz

Jan 2015 @sandimetz New Feature Request:

Jan 2015 @sandimetz New Feature Request: RandomHouse

Jan 2015 @sandimetz [ 'the horse and
the hound and the horn that belonged to', 'the farmer sowing his corn that kept', 'the rooster that crowed in the morn that woke', 'the priest all shaven and shorn that married', 'the man all tattered and torn that kissed', 'the maiden all forlorn that milked', 'the cow with the crumpled horn that tossed', 'the dog that worried', 'the cat that killed', 'the rat that ate', 'the malt that lay in', 'the house that Jack built' ]

Jan 2015 @sandimetz [ 'the rooster that
crowed in the morn that woke', 'the farmer sowing his corn that kept', 'the dog that worried', 'the priest all shaven and shorn that married', 'the man all tattered and torn that kissed', 'the horse and the hound and the horn that belonged to', 'the malt that lay in', 'the cow with the crumpled horn that tossed', 'the house that Jack built', 'the cat that killed', 'the maiden all forlorn that milked', 'the rat that ate']

Jan 2015 @sandimetz 'This is the rat that ate.'
1

'This is the maiden all forlorn that milked the rat that ate.' 1 2

'This is the maiden all forlorn that milked the rat that ate.' 'This is the cat that killed the maiden all forlorn that milked the rat that ate.' 1 2 3

'This is the maiden all forlorn that milked the rat that ate.' 'This is the cat that killed the maiden all forlorn that milked the rat that ate.' 'This is the rooster that crowed in the morn that woke the farmer sowing his corn that kept the dog that worried the priest all shaven and shorn that married the man all tattered and torn that kissed the horse and the hound and the horn that belonged to the malt that lay in the cow with the crumpled horn that tossed the house that Jack built the cat that killed the maiden all forlorn that milked the rat that ate.' 12

def line(number) def phrase(number) def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end

def line(number) def phrase(number) def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end Task: Implement RandomHouse without 'if' statements

def line(number) def phrase(number) def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end Inheritance?

def line(number) def phrase(number) def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end class RandomHouse < House def data @data ||= super.shuffle end end

Jan 2015 @sandimetz

Jan 2015 @sandimetz randomhouse = RandomHouse.new

Jan 2015 @sandimetz randomhouse = RandomHouse.new puts randomhouse.line(1) => 'This
is the rat that ate.'

is the rat that ate.' puts randomhouse.line(2) => 'This is the maiden all forlorn that milked the rat that ate.'

is the rat that ate.' puts randomhouse.line(2) => 'This is the maiden all forlorn that milked the rat that ate.' puts randomhouse.line(3) => 'This is the cat that killed the maiden all forlorn that milked the rat that ate.'

is the rat that ate.' puts randomhouse.line(2) => 'This is the maiden all forlorn that milked the rat that ate.' puts randomhouse.line(3) => 'This is the cat that killed the maiden all forlorn that milked the rat that ate.' puts randomhouse.line(12) => 'This is the rooster that crowed in the morn that woke the farmer sowing his corn that kept the dog that worried the priest all shaven and shorn that married the man all tattered and torn that kissed the horse and the hound and the horn that belonged to the malt that lay in the cow with the crumpled horn that tossed the house that Jack built the cat that killed the maiden all forlorn that milked the rat that ate.'

Jan 2015 @sandimetz

Jan 2015 @sandimetz New Feature Request: EchoHouse

Jan 2015 @sandimetz

Jan 2015 @sandimetz This is the house that Jack built
the house that Jack built.

the house that Jack built. This is the malt that lay in the malt that lay in the house that Jack built the house that Jack built.

the house that Jack built. This is the malt that lay in the malt that lay in the house that Jack built the house that Jack built. This is the rat that ate the rat that ate the malt that lay in the malt that lay in the house that Jack built the house that Jack built.

(1..data.length).map {|i| line(i)}.join("\n") end def line(number) "This is #{phrase(number)}.\n" end def phrase(number) data.last(number).join(" ") end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end

def line(number) def phrase(number) data.last(number).join(" ") end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end

def line(number) def phrase(number) data.last(number).join(" ") end def parts(number) end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end

def line(number) def phrase(number) data.last(number).join(" ") end def parts(number) data.last(number) end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end

def line(number) def phrase(number) parts(number).join(" ") end def parts(number) data.last(number) end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end

def line(number) def phrase(number) def parts(number) data.last(number) end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end

def line(number) def phrase(number) def parts(number) data.last(number) end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end ['the rat that ate', 'the malt that lay in', 'the house that Jack built'] have

def line(number) def phrase(number) def parts(number) data.last(number) end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end ['the rat that ate', 'the malt that lay in', 'the house that Jack built'] ['the rat that ate', 'the rat that ate', 'the malt that lay in', 'the malt that lay in', 'the house that Jack built', 'the house that Jack built'] want

def line(number) def phrase(number) def parts(number) data.last(number) end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end

def line(number) def phrase(number) def parts(number) data.last(number) end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end Task: Implement EchoHouse without 'if' statements

def line(number) def phrase(number) def parts(number) data.last(number) end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end Inheritance?

def line(number) def phrase(number) def parts(number) data.last(number) end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end class EchoHouse < House def parts(number) super.zip(super).flatten end end

Jan 2015 @sandimetz ['the rat that ate', 'the malt
that lay in', 'the house that Jack built']

that lay in', 'the house that Jack built'] ['the rat that ate', 'the malt that lay in', 'the house that Jack built']

that lay in', 'the house that Jack built'] ['the rat that ate', 'the malt that lay in', 'the house that Jack built'] super.zip(super)

that lay in', 'the house that Jack built'] ['the rat that ate', 'the malt that lay in', 'the house that Jack built'] [['the rat that ate','the rat that ate'], ['the malt that lay in','the malt that lay in'], ['the house that Jack built','the house that Jack built']] super.zip(super)

that lay in', 'the house that Jack built'] super.zip(super).flatten ['the rat that ate', 'the malt that lay in', 'the house that Jack built'] [['the rat that ate','the rat that ate'], ['the malt that lay in','the malt that lay in'], ['the house that Jack built','the house that Jack built']] super.zip(super)

that lay in', 'the house that Jack built'] super.zip(super).flatten ['the rat that ate', 'the malt that lay in', 'the house that Jack built'] [['the rat that ate','the rat that ate'], ['the malt that lay in','the malt that lay in'], ['the house that Jack built','the house that Jack built']] super.zip(super) ['the rat that ate','the rat that ate', 'the malt that lay in','the malt that lay in', 'the house that Jack built','the house that Jack built']

def line(number) def phrase(number) def parts(number) data.last(number) end def data [ 'the horse and the hound and the horn that belonged to', # ... 'the malt that lay in', 'the house that Jack built'] end end class EchoHouse < House def parts(number) super.zip(super).flatten end end

Jan 2015 @sandimetz

Jan 2015 @sandimetz puts EchoHouse.new.line(1) 'This is the house that
Jack built the house that Jack built.'

Jack built the house that Jack built.' puts EchoHouse.new.line(2) 'This is the malt that lay in the malt that lay in the house that Jack built the house that Jack built.'

Jack built the house that Jack built.' puts EchoHouse.new.line(2) 'This is the malt that lay in the malt that lay in the house that Jack built the house that Jack built.' puts EchoHouse.new.line(3) 'This is the rat that ate the rat that ate the malt that lay in the malt that lay in the house that Jack built the house that Jack built.'

Jack built the house that Jack built.' puts EchoHouse.new.line(2) 'This is the malt that lay in the malt that lay in the house that Jack built the house that Jack built.' puts EchoHouse.new.line(3) 'This is the rat that ate the rat that ate the malt that lay in the malt that lay in the house that Jack built the house that Jack built.' puts EchoHouse.new.line(12) 'This is the horse and the hound and the horn that belonged to the horse and the hound and the horn that belonged to the farmer sowing his corn that kept the farmer sowing his corn that kept the rooster that crowed in the morn that woke the rooster that crowed in the morn that woke the priest all shaven and shorn that married the priest all shaven and shorn that married the man all tattered and torn that kissed the man all tattered and torn that kissed the maiden all forlorn that milked the maiden all forlorn that milked the cow with the crumpled horn that tossed the cow with the crumpled horn that tossed the dog that worried the dog that worried the cat that killed the cat that killed the rat that ate the rat that ate the malt that lay in the malt that lay in the house that Jack built the house that Jack built.'

def line(number) def phrase(number) def parts(number) def data end

Jan 2015 @sandimetz class RandomHouse < House def
data @data ||= super.shuffle end end class House def recite def line(number) def phrase(number) def parts(number) def data end

data @data ||= super.shuffle end end class EchoHouse < House def parts(number) super.zip(super).flatten end end class House def recite def line(number) def phrase(number) def parts(number) def data end

data @data ||= super.shuffle end end class EchoHouse < House def parts(number) super.zip(super).flatten end end class House def recite def line(number) def phrase(number) def parts(number) def data end What could possibly go wrong?

Jan 2015 @sandimetz

Jan 2015 @sandimetz New Feature Request: RandomEchoHouse

data @data ||= super.shuffle end end class EchoHouse < House def parts(number) super.zip(super).flatten end end class House def recite def line(number) def phrase(number) def parts(number) def data end

data @data ||= super.shuffle end end class EchoHouse < House def parts(number) super.zip(super).flatten end end

data @data ||= super.shuffle end end class EchoHouse < House def parts(number) super.zip(super).flatten end end Duplicate some of the code?

data @data ||= super.shuffle end end class EchoHouse < House def parts(number) super.zip(super).flatten end end RandomEchoHouse < RandomHouse < EchoHouse data parts

data @data ||= super.shuffle end end class RandomEchoHouse < RandomHouse def parts(number) super.zip(super).flatten end end class EchoHouse < House def parts(number) super.zip(super).flatten end end RandomEchoHouse < RandomHouse < EchoHouse data parts

data @data ||= super.shuffle end end class RandomEchoHouse < RandomHouse def parts(number) super.zip(super).flatten end end class EchoHouse < House def parts(number) super.zip(super).flatten end end RandomEchoHouse < RandomHouse < EchoHouse Inherit data parts

data @data ||= super.shuffle end end class RandomEchoHouse < RandomHouse def parts(number) super.zip(super).flatten end end class EchoHouse < House def parts(number) super.zip(super).flatten end end RandomEchoHouse < RandomHouse < EchoHouse Inherit data Duplicate parts

data @data ||= super.shuffle end end class EchoHouse < House def parts(number) super.zip(super).flatten end end RandomEchoHouse < RandomHouse < EchoHouse Inherit data Duplicate parts

data @data ||= super.shuffle end end class EchoHouse < House def parts(number) super.zip(super).flatten end end class RandomEchoHouse < EchoHouse def data @data ||= super.shuffle end end RandomEchoHouse < RandomHouse < EchoHouse Inherit data Duplicate parts

data @data ||= super.shuffle end end class EchoHouse < House def parts(number) super.zip(super).flatten end end class RandomEchoHouse < EchoHouse def data @data ||= super.shuffle end end RandomEchoHouse < RandomHouse < EchoHouse Inherit data Duplicate parts Inherit

data @data ||= super.shuffle end end class EchoHouse < House def parts(number) super.zip(super).flatten end end class RandomEchoHouse < EchoHouse def data @data ||= super.shuffle end end RandomEchoHouse < RandomHouse < EchoHouse Inherit data Duplicate Duplicate parts Inherit

Jan 2015 @sandimetz class RandomHouse < House class EchoHouse
< House

< House Duplicate all of the code!

< House class RandomEchoHouse < House

data @data ||= super.shuffle end end class EchoHouse < House def parts(number) super.zip(super).flatten end end class RandomEchoHouse < House def data @data ||= super.shuffle end def parts(number) super.zip(super).flatten end end

Jan 2015 @sandimetz House

Jan 2015 @sandimetz House Random House Echo House

Jan 2015 @sandimetz House Echo House Random House

Jan 2015 @sandimetz House Echo House Random House Random House

Jan 2015 @sandimetz House Echo House Random House Random House
Echo House

Jan 2015 @sandimetz Echo House Random House Random House Echo
House

Jan 2015 @sandimetz Random House Echo House

Jan 2015 @sandimetz Random House Echo House RandomEcho House

Jan 2015 @sandimetz Random House Echo House

Jan 2015 @sandimetz

Jan 2015 @sandimetz Inheritance

Jan 2015 @sandimetz Inheritance is for specialization

Jan 2015 @sandimetz Inheritance is for specialization is not for
sharing code

Jan 2015 @sandimetz RandomHouse is-a House?

Jan 2015 @sandimetz class House def data
[ 'the horse and the hound and the horn that belonged to', 'the farmer sowing his corn that kept', 'the rooster that crowed in the morn that woke', 'the priest all shaven and shorn that married', 'the man all tattered and torn that kissed', 'the maiden all forlorn that milked', 'the cow with the crumpled horn that tossed', 'the dog that worried', 'the cat that killed', 'the rat that ate', 'the malt that lay in', 'the house that Jack built'] end end class RandomHouse < House def data @data ||= super.shuffle end end

[ 'the horse and the hound and the horn that belonged to', 'the farmer sowing his corn that kept', 'the rooster that crowed in the morn that woke', 'the priest all shaven and shorn that married', 'the man all tattered and torn that kissed', 'the maiden all forlorn that milked', 'the cow with the crumpled horn that tossed', 'the dog that worried', 'the cat that killed', 'the rat that ate', 'the malt that lay in', 'the house that Jack built'] end end class RandomHouse < House def data @data ||= super.shuffle end end What does RandomHouse change?

Jan 2015 @sandimetz Reveal how things diﬀer by making them
more alike

[ 'the horse and the hound and the horn that belonged to', 'the farmer sowing his corn that kept', 'the rooster that crowed in the morn that woke', 'the priest all shaven and shorn that married', 'the man all tattered and torn that kissed', 'the maiden all forlorn that milked', 'the cow with the crumpled horn that tossed', 'the dog that worried', 'the cat that killed', 'the rat that ate', 'the malt that lay in', 'the house that Jack built'] end end class RandomHouse < House def data @data ||= super.shuffle end end

[ 'the horse and the hound and the horn that belonged to', 'the farmer sowing his corn that kept', 'the rooster that crowed in the morn that woke', 'the priest all shaven and shorn that married', 'the man all tattered and torn that kissed', 'the maiden all forlorn that milked', 'the cow with the crumpled horn that tossed', 'the dog that worried', 'the cat that killed', 'the rat that ate', 'the malt that lay in', 'the house that Jack built'] end end class RandomHouse < House def data @data ||= super.shuffle end end Make this

[ 'the horse and the hound and the horn that belonged to', 'the farmer sowing his corn that kept', 'the rooster that crowed in the morn that woke', 'the priest all shaven and shorn that married', 'the man all tattered and torn that kissed', 'the maiden all forlorn that milked', 'the cow with the crumpled horn that tossed', 'the dog that worried', 'the cat that killed', 'the rat that ate', 'the malt that lay in', 'the house that Jack built'] end end class RandomHouse < House def data @data ||= super.shuffle end end Make this More like this

[ 'the horse and the hound and the horn that belonged to', 'the farmer sowing his corn that kept', 'the rooster that crowed in the morn that woke', 'the priest all shaven and shorn that married', 'the man all tattered and torn that kissed', 'the maiden all forlorn that milked', 'the cow with the crumpled horn that tossed', 'the dog that worried', 'the cat that killed', 'the rat that ate', 'the malt that lay in', 'the house that Jack built'] end end

Jan 2015 @sandimetz class House DATA =
[ 'the horse and the hound and the horn that belonged to', 'the farmer sowing his corn that kept', 'the rooster that crowed in the morn that woke', 'the priest all shaven and shorn that married', 'the man all tattered and torn that kissed', 'the maiden all forlorn that milked', 'the cow with the crumpled horn that tossed', 'the dog that worried', 'the cat that killed', 'the rat that ate', 'the malt that lay in', 'the house that Jack built'] end

[ 'the horse and the hound and the horn that belonged to', # ... 'the house that Jack built'] end

[ 'the horse and the hound and the horn that belonged to', # ... 'the house that Jack built'] def data DATA end end

[ 'the horse and the hound and the horn that belonged to', # ... 'the house that Jack built'] def data DATA end end class RandomHouse < House def data @data ||= super.shuffle end end

[ 'the horse and the hound and the horn that belonged to', # ... 'the house that Jack built'] def data @data ||= DATA end end class RandomHouse < House def data @data ||= super.shuffle end end

[ 'the horse and the hound and the horn that belonged to', # ... 'the house that Jack built'] def data @data ||= DATA end end class RandomHouse < House def data @data ||= DATA.shuffle end end

[ 'the horse and the hound and the horn that belonged to', # ... 'the house that Jack built'] def data @data ||= DATA end end class RandomHouse < House def data @data ||= DATA.shuffle end end What changed?

Jan 2015 @sandimetz Name the concept

Jan 2015 @sandimetz House RandomHouse

Jan 2015 @sandimetz House DATA RandomHouse DATA

Jan 2015 @sandimetz House DATA RandomHouse DATA shuffle

Jan 2015 @sandimetz class House DATA RandomHouse DATA shuffle

Jan 2015 @sandimetz class data House DATA RandomHouse DATA shuffle

Jan 2015 @sandimetz class data ????? House DATA RandomHouse DATA
shuffle

Jan 2015 @sandimetz class data random?? House DATA RandomHouse DATA
shuffle

Jan 2015 @sandimetz class data order! House DATA RandomHouse DATA
shuffle

Jan 2015 @sandimetz class data order House DATA RandomHouse DATA
shuffle

shuffle This is not nothing

shuffle It's an order algorithm

shuffle It's an order algorithm just as valid as this one

Jan 2015 @sandimetz Order is-a House?

Jan 2015 @sandimetz Orderer is a role

Jan 2015 @sandimetz class RandomOrder def order(data)
data.shuffle end end

Jan 2015 @sandimetz class DefaultOrder end class RandomOrder
def order(data) data.shuffle end end

Jan 2015 @sandimetz class DefaultOrder def order(data)
end end class RandomOrder def order(data) data.shuffle end end

data end end class RandomOrder def order(data) data.shuffle end end

[ 'the horse and the hound and the horn that belonged to', # ... 'the house that Jack built'] def data DATA end end class RandomHouse < House def data @data ||= super.shuffle end end

[ 'the horse and the hound and the horn that belonged to', # ... 'the house that Jack built'] def data DATA end end

[ 'the horse and the hound and the horn that belonged to', # ... 'the house that Jack built'] def data DATA end # ... end

[ 'the horse and the hound and the horn that belonged to', # ... 'the house that Jack built'] attr_reader :data def data DATA end # ... end

[ 'the horse and the hound and the horn that belonged to', # ... 'the house that Jack built'] attr_reader :data def initialize @data = DATA end def data DATA end # ... end

[ 'the horse and the hound and the horn that belonged to', # ... 'the house that Jack built'] attr_reader :data def initialize @data = DATA end # ... end

Jan 2015 @sandimetz class House attr_reader :data
def initialize @data = DATA end # ... end

def initialize @data = DATA end # ... end Remove 'ordering' responsibility from House

def initialize @data = DATA end # ... end class DefaultOrder def order(data) data end end

def initialize(orderer: DefaultOrder.new) @data = DATA end # ... end class DefaultOrder def order(data) data end end

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultOrder def order(data) data end end

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultOrder def order(data) data end end puts House.new.line(12)

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultOrder def order(data) data end end puts House.new.line(12) => 'This is the horse and the hound and the horn that belonged to the farmer sowing his corn that kept the rooster that crowed in the morn that woke the priest all shaven and shorn that married the man all tattered and torn that kissed the maiden all forlorn that milked the cow with the crumpled horn that tossed the dog that worried the cat that killed the rat that ate the malt that lay in the house that Jack built.'

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultOrder def order(data) data end end puts House.new.line(12) => 'This is the horse and the hound and the horn that belonged to the farmer sowing his corn that kept the rooster that crowed in the morn that woke the priest all shaven and shorn that married the man all tattered and torn that kissed the maiden all forlorn that milked the cow with the crumpled horn that tossed the dog that worried the cat that killed the rat that ate the malt that lay in the house that Jack built.' More code

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultOrder def order(data) data end end puts House.new.line(12) => 'This is the horse and the hound and the horn that belonged to the farmer sowing his corn that kept the rooster that crowed in the morn that woke the priest all shaven and shorn that married the man all tattered and torn that kissed the maiden all forlorn that milked the cow with the crumpled horn that tossed the dog that worried the cat that killed the rat that ate the malt that lay in the house that Jack built.' More code Same behavior

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultOrder def order(data) data end end puts House.new.line(12) => 'This is the horse and the hound and the horn that belonged to the farmer sowing his corn that kept the rooster that crowed in the morn that woke the priest all shaven and shorn that married the man all tattered and torn that kissed the maiden all forlorn that milked the cow with the crumpled horn that tossed the dog that worried the cat that killed the rat that ate the malt that lay in the house that Jack built.' More code Same behavior Awesome

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultOrder def order(data) data end end puts House.new.line(12) => 'This is the horse and the hound and the horn that belonged to the farmer sowing his corn that kept the rooster that crowed in the morn that woke the priest all shaven and shorn that married the man all tattered and torn that kissed the maiden all forlorn that milked the cow with the crumpled horn that tossed the dog that worried the cat that killed the rat that ate the malt that lay in the house that Jack built.'

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultOrder def order(data) data end end puts House.new.line(12) class RandomOrder def order(data) data.shuffle end end

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultOrder def order(data) data end end puts House.new( ).line(12) class RandomOrder def order(data) data.shuffle end end

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultOrder def order(data) data end end puts House.new(orderer: RandomOrder.new).line(12) class RandomOrder def order(data) data.shuffle end end

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultOrder def order(data) data end end puts House.new(orderer: RandomOrder.new).line(12) => 'This is the rooster that crowed in the morn that woke the farmer sowing his corn that kept the dog that worried the priest all shaven and shorn that married the man all tattered and torn that kissed the horse and the hound and the horn that belonged to the malt that lay in the cow with the crumpled horn that tossed the house that Jack built the cat that killed the maiden all forlorn that milked the rat that ate.' class RandomOrder def order(data) data.shuffle end end

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultOrder def order(data) data end end puts House.new(orderer: RandomOrder.new).line(12) => 'This is the rooster that crowed in the morn that woke the cat that killed the cow with the crumpled horn that tossed the horse and the hound and the horn that belonged to the farmer sowing his corn that kept the priest all shaven and shorn that married the man all tattered and torn that kissed the house that Jack built the malt that lay in the rat that ate the maiden all forlorn that milked the dog that worried.' class RandomOrder def order(data) data.shuffle end end Composition

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultOrder def order(data) data end end puts House.new(orderer: RandomOrder.new).line(12) => 'This is the rooster that crowed in the morn that woke the cat that killed the cow with the crumpled horn that tossed the horse and the hound and the horn that belonged to the farmer sowing his corn that kept the priest all shaven and shorn that married the man all tattered and torn that kissed the house that Jack built the malt that lay in the rat that ate the maiden all forlorn that milked the dog that worried.' class RandomOrder def order(data) data.shuffle end end Inject an object to play the role of the thing that varies

Jan 2015 @sandimetz Echo?

Jan 2015 @sandimetz class EchoFormatter def format(parts)
parts.zip(parts).flatten end end

Jan 2015 @sandimetz class DefaultFormatter def format(parts)
parts end end class EchoFormatter def format(parts) parts.zip(parts).flatten end end

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end

def initialize(orderer: DefaultOrder.new) @data = orderer.order(DATA) end # ... end class DefaultFormatter def format(parts) parts end end

def initialize(orderer: DefaultOrder.new, formatter: DefaultFormatter.new) @data = orderer.order(DATA) end # ... end class DefaultFormatter def format(parts) parts end end

def initialize(orderer: DefaultOrder.new, formatter: DefaultFormatter.new) @formatter = formatter @data = orderer.order(DATA) end # ... end class DefaultFormatter def format(parts) parts end end

Jan 2015 @sandimetz class House attr_reader
:data def initialize(orderer: DefaultOrder.new, formatter: DefaultFormatter.new) @formatter = formatter @data = orderer.order(DATA) end # ... end class DefaultFormatter def format(parts) parts end end

Jan 2015 @sandimetz class House attr_reader :formatter, :data

def initialize(orderer: DefaultOrder.new, formatter: DefaultFormatter.new) @formatter = formatter @data = orderer.order(DATA) end def parts(number) data.last(number) end # ... end class DefaultFormatter def format(parts) parts end end

def initialize(orderer: DefaultOrder.new, formatter: DefaultFormatter.new) @formatter = formatter @data = orderer.order(DATA) end def parts(number) formatter.format(data.last(number)) end # ... end class DefaultFormatter def format(parts) parts end end

def initialize(orderer: DefaultOrder.new, formatter: DefaultFormatter.new) @formatter = formatter @data = orderer.order(DATA) end # ... end puts House.new.line(12) class DefaultFormatter def format(parts) parts end end

def initialize(orderer: DefaultOrder.new, formatter: DefaultFormatter.new) @formatter = formatter @data = orderer.order(DATA) end # ... end puts House.new.line(12) => 'This is the horse and the hound and the horn that belonged to the farmer sowing his corn that kept the rooster that crowed in the morn that woke the priest all shaven and shorn that married the man all tattered and torn that kissed the maiden all forlorn that milked the cow with the crumpled horn that tossed the dog that worried the cat that killed the rat that ate the malt that lay in the house that Jack built.' class DefaultFormatter def format(parts) parts end end

parts end end class House attr_reader :formatter, :data def initialize(orderer: DefaultOrder.new, formatter: DefaultFormatter.new) @formatter = formatter @data = orderer.order(DATA) end # ... end class EchoFormatter def format(parts) parts.zip(parts).flatten end end

parts end end class House attr_reader :formatter, :data def initialize(orderer: DefaultOrder.new, formatter: DefaultFormatter.new) @formatter = formatter @data = orderer.order(DATA) end # ... end puts House.new(formatter: EchoFormatter.new).line(12) class EchoFormatter def format(parts) parts.zip(parts).flatten end end

parts end end class House attr_reader :formatter, :data def initialize(orderer: DefaultOrder.new, formatter: DefaultFormatter.new) @formatter = formatter @data = orderer.order(DATA) end # ... end puts House.new(formatter: EchoFormatter.new).line(12) => 'This is the horse and the hound and the horn that belonged to the horse and the hound and the horn that belonged to the farmer sowing his corn that kept the farmer sowing his corn that kept the rooster that crowed in the morn that woke the rooster that crowed in the morn that woke the priest all shaven and shorn that married the priest all shaven and shorn that married the man all tattered and torn that kissed the man class EchoFormatter def format(parts) parts.zip(parts).flatten end end

data end end class RandomOrder def order(data) data.shuffle end end Orderer Role

parts end end class EchoFormatter def format(parts) parts.zip(parts).flatten end end class DefaultOrder def order(data) data end end class RandomOrder def order(data) data.shuffle end end Orderer Role Formatter Role

Jan 2015 @sandimetz puts House.new.line(12)

Jan 2015 @sandimetz

Jan 2015 @sandimetz puts House.new.recite

Jan 2015 @sandimetz puts House.new.recite puts House.new(orderer: RandomOrder.new).recite

Jan 2015 @sandimetz puts House.new.recite puts House.new(orderer: RandomOrder.new).recite puts House.new(formatter:
EchoFormatter.new).recite

Jan 2015 @sandimetz puts House.new.recite puts House.new(orderer: RandomOrder.new).recite puts House.new(formatter:
EchoFormatter.new).recite puts House.new(orderer: RandomOrder.new, formatter: EchoFormatter.new).recite

puts House.new(formatter: EchoFormatter.new).recite puts House.new(orderer: RandomOrder.new, formatter: EchoFormatter.new).recite More code?

puts House.new(formatter: EchoFormatter.new).recite puts House.new(orderer: RandomOrder.new, formatter: EchoFormatter.new).recite

puts House.new(formatter: EchoFormatter.new).recite puts House.new(orderer: RandomOrder.new, formatter: EchoFormatter.new).recite Less code!

puts House.new(formatter: EchoFormatter.new).recite puts House.new(orderer: RandomOrder.new, formatter: EchoFormatter.new).recite Less code! No duplication

puts House.new(formatter: EchoFormatter.new).recite puts House.new(orderer: RandomOrder.new, formatter: EchoFormatter.new).recite Less code! Pluggable behavior

Jan 2015 @sandimetz House Echo House Random House

Jan 2015 @sandimetz House 1) Isolate the thing that varies

Jan 2015 @sandimetz House 2) Name the Concept

Jan 2015 @sandimetz House Order Format

Jan 2015 @sandimetz House Order Format 3) Deﬁne the Role

Jan 2015 @sandimetz House Orderer Formatter

Jan 2015 @sandimetz House Orderer Formatter 4) Inject the player

Jan 2015 @sandimetz House Orderer Formatter

puts House.new(formatter: EchoFormatter.new).recite puts House.new(orderer: RandomOrder.new, formatter: EchoFormatter.new).recite

puts House.new(formatter: EchoFormatter.new).recite puts House.new(orderer: RandomOrder.new, formatter: EchoFormatter.new).recite Composition

puts House.new(formatter: EchoFormatter.new).recite puts House.new(orderer: RandomOrder.new, formatter: EchoFormatter.new).recite Composition + Dependency Injection

puts House.new(formatter: EchoFormatter.new).recite puts House.new(orderer: RandomOrder.new, formatter: EchoFormatter.new).recite Object-Oriented Design

Jan 2015 @sandimetz Smalltalk Infected Condition Averse Message Centric Abstraction
Seeking

Jan 2015 @sandimetz Summary

Jan 2015 @sandimetz

Jan 2015 @sandimetz If you're talking to nil

Jan 2015 @sandimetz If you're talking to nil it's something

Jan 2015 @sandimetz Null Object Pattern Active Nothing

Jan 2015 @sandimetz

Jan 2015 @sandimetz Ware Inheritance

Jan 2015 @sandimetz Ware Inheritance It is not for sharing
behavior

Jan 2015 @sandimetz There's no such thing as one specialization

Jan 2015 @sandimetz

Jan 2015 @sandimetz Isolate the thing that varies

Jan 2015 @sandimetz Isolate the thing that varies Name the
concept

concept Deﬁne the role

concept Deﬁne the role Inject the players

Jan 2015 @sandimetz Believe in nothing

Jan 2015 @sandimetz Nothing is always Something

Jan 2015 @sandimetz Sandi Metz @sandimetz http://sandimetz.com

Jan 2015 @sandimetz http://poodr.com

Jan 2015 @sandimetz http://99bottlesbook.com Practical Programming Book 99 Bottles of
OOP

Jan 2015 @sandimetz Next Public Course POODNYC Oct 19-21, 2015
New York City

Jan 2015 @sandimetz Stickers?

Jan 2015 @sandimetz Temporary Tattoos!

Jan 2015 @sandimetz Thanks

Jan 2015 @sandimetz Sandi Metz @sandimetz http://sandimetz.com

Nothing is Something (RailsConf)

Nothing is Something (RailsConf)

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