This document discusses immutability in Ruby. It explains that immutable data structures can improve predictability, consistency, and scalability for multi-threaded and distributed applications. While immutable structures may have lower performance for certain operations like random access, there are patterns like using immutable objects and transforming data instead of mutating it that can provide the benefits of immutability in Ruby applications. The document also provides examples of implementing immutable user objects that can be validated and updated without directly mutating the original data.

1. Imutabilidade em
Ruby

2. Bom dia!
Maurício Szabo
http://mauricio.szabo.link

3. Imutabilidade?
Em Ruby?
Por quê?

4. But Why!?
Concorrencia
Multi-thread
Escalabilidade horizontal
Blablabla...
Previsibilidade
Consistência
Replicabilidade
Composição
Mantenabilidade

5. Previsibilidade

6. Consistência
age = 18age = 28
Person 1
Person 2
Task 1
Task 2
Task 3
Task 4

7. Replicabilidade
f(10, 20, 30) 42

8. Replicabilidade
f(10, 20, 30) 42

9. Replicabilidade
rand() 0.01090
f(10, 20, 30)

10. Replicabilidade
rand() 0.92100
f(10, 20, 30)

11. h
Funções Puras
randf
g
h

12. Ruby, Finalmente
Estruturas de Dados Imutáveis
1
https://bit.ly/2JjCUzE

13. Estruturas
Hamster::Vector[]
Hamster::Deque[]
Hamster::List[]
Hamster::Set[]
Hamster::Hash[]
Acesso via
indice
push /
append
pop /
drop_last
unshift /
prepend
shift / tail

14. Performance?
Spoiler: é mais lento!

15. Lista de Elementos
(prepend)
real
Mutable array - unshift 0.050518
Mutable array - shift 0.028875
Immutable list - unshift 0.342788
(6.8x mais lento)
Immutable list - shift 0.028016
(+/- mesma velocidade)

16. Lista de Elementos
real
Mutable array - push 0.047483
Mutable array - pop 0.029408
Mutable array - unshift 0.050518
Mutable array - shift 0.028875
Immutable deque - append at last 0.537605 (11x mais lento)
Immutable deque - pop 0.179720 (6x mais lento)
Immutable deque - append at first 0.496692 (9.5x mais lento)
Immutable deque - shift 0.172747 (6x mais lento)

17. Random Access
real
Mutable array 0.047483
Mutable array - get random element 0.047016
Mutable array - pop 0.029408
Immutable vector 1.782584
(37x mais lento!!!)
Immutable vector - get random element 0.213734
(4.5x mais lento)
Immutable vector - pop 4.246951
(144x mais lento!!!)

18. “Hack”
real
Mutable array 0.343495
Immutable list - prepend 3.075296 (10x mais lento)
Immutable list - from mutable 0.955190 (3.7x mais lento)
Immutable Deque - from mutable 0.947304 (3.7x mais lento)
Immutable Vector - from mutable 0.299589 (1.8x mais lento)

19. Objetos!
Trabalhando com instâncias
imutáveis

20. An object has state (data)
and behavior (code)
(Wikipedia)
Wikipedia is not a reliable source
(Every university professor)

21. class User
include Anima.new(:name, :email)
end
user = User.new(name: "Foo", email: "foo@bar.com")
user.email << ".br"
user.email # => "foo@bar.com.br"
def user.nada
"#{name} = #{email}"
end
user.nada # => "Foo = foo@bar.com.br"
class User
include Anima.new(:name, :email)
include Adamantium
end
user = User.new(name: "Foo", email: "foo@bar.com")
user.email << ".br" # => can’t modify frozen object
def user.nada
"#{name} = #{email}"
end # => can’t modify frozen object

22. class User
include Anima.new(:name, :email)
end
user = User.new(name: "Foo", email: "foo@bar.com")
user2 = user.with(email: "other@email.com")
user.email # => "foo@bar.com"
user2.email # => "other@email.com"
Como trabalhar?

23. Padrões - Data First
class User
include Anima.new(:name, :children)
include UpInAnima
NULL = new(name: "", children: Hamster::Vector[])
end
class Children
include Anima.new(:name, :age)
include UpInAnima
NULL = new(name: "", age: 0)
end

24. Padrões - Data First
https://bit.ly/2JjCUzE
user = User::NULL
.with(name: "Ariovaldo")
.update_in(:children) { |c|
c.add(Children::NULL.with(name: "Emily",
age: 9))
}
# Emily's birthday!
user.update_in(:children, 0, :age) { |age|
age + 1
}

25. Banco de Dados
Datasets imutáveis, Sequel, ROM,
ActiveRecord, etc...

26. Bancos de Dados
id = 1
age = 9
id = 1
age = 10 Validate
id = 1
age = 10

27. Either Monad
Dados
Dados
Transformados
Dados
Transformados’
Erros
Erros
Erros
UPDATE!
Validate
Dados para
Update

28. Talk is Easy...
class User
extend Sequel::Model::ClassMethods
include Anima.new(:id, :name, :email)
self.dataset = DB[:users]
def self.call(param)
new(param)
end
def update!(params)
validate(params).then do |new_obj|
pk = self.class.primary_key
pk_value = send(pk)
self.class.dataset.where(pk => pk_value).update(new_obj.to_h)
new_obj
end
end
private :with
private def validate(params)
new_obj = with(params)
errors = NameValidation.call(new_obj.to_h).errors
if(errors.empty?)
Either.right(new_obj)
else
Either.left(errors)
end
end
end

29. class User
extend Sequel::Model::ClassMethods
include Anima.new(:id, :name, :email)
self.dataset = DB[:users]
def self.call(param)
new(param)
end
# ...
end

30. class User
# …
private def validate(params)
new_obj = with(params)
errors = NameValidation.call(new_obj.to_h).error
if(errors.empty?)
Either.right(new_obj)
else
Either.left(errors)
end
end
end

31. class User
# ...
def update!(params)
validate(params).then do |new_obj|
pk = self.class.primary_key
pk_value = send(pk)
self.class.dataset
.where(pk => pk_value)
.update(new_obj.to_h)
new_obj
end
End
private :with
# ...
end

32. u2 = u.update!(name: "") # => Either left=....
User.first
# => #<User id=1 name="Foo Bar" email=nil>
u2 = u.update!(email: "szabo@mailinator.com")
User.first
# => #<User id=1 name="Foo Bar" email="szabo@mailinator.com">
u2 = u.update!(name: "Szabo")
User.first
# => #<User id=1 name="Szabo" email=nil>
u = User.first
# => #<User id=1 name="Foo Bar" email=nil>

33. Transformação
Imutável
Dado FN
Dado
Alterado

34. []’s
Perguntas?
Meus links:
◇ http://mauricio.szabo.link
◇ mauricio.szabo@gmail.com
◇ https://bit.ly/2JjCUzE