This document discusses some common "gotchas" or surprises that newcomers to Ruby may encounter. It covers topics like truthy and falsey values in Ruby (only nil and false are falsey), the difference between and and && operators (and has higher precedence than =), that constants can be reassigned, and the differences between blocks, procs, and lambdas. The document is intended to help new Ruby programmers avoid surprises by explaining behaviors that may differ from other languages. It includes code examples to illustrate each point and provides references for further reading.

1. RUBY GOTCHAS
Algumas surpresas que esperam os novatos

2. Sobre mim
• Programador
• Trabalho no Glio
• Novato em Ruby
• @nelson_senna no Twitter

3. Motivação

4. –Yukihiro “Matz” Matsumoto
“Ruby is simple in appearance, but is very
complex inside, just like our human body.”

5. Ruby pode ser
surpreendente!

6. Mágica!

7. No fim tudo é um
objeto

8. Gotcha #1
O que é verdade?

9. 2.3.0 :001 > 0 ? true : false

10. 2.3.0 :001 > 0 ? true : false
=> true

11. 2.3.0 :001 > ‘’ ? true : false

12. 2.3.0 :001 > ‘’ ? true : false
=> true

13. 2.3.0 :001 > [] ? true : false

14. 2.3.0 :001 > [] ? true : false
=> true

15. 2.3.0 :001 > nil ? true : false

16. 2.3.0 :001 > nil ? true : false
=> false

17. 2.3.0 :001 > false ? true : false

18. 2.3.0 :001 > false ? true : false
=> false

19. A pegadinha
Em Ruby só nil e false são considerados “falsey”
qualquer outro valor é considerado “truthy”.

20. Isso é útil?
address = ‘Rua Casa do Ator, 275’
address2 = nil # Famoso complemento
full_address = “Endereço: #{address}n
#{“Complemento: #{address2}” if address2}”

21. Gotcha #2
(&& ou and) e (|| ou or)?

22. song = { name: 'Nelson', duration: 300 }
duration = song[:duration]
minutes = duration && duration / 60
puts minutes # imprime 5
Duração em minutos

23. song = { name: 'Nelson', duration: 300 }
duration = song[:duration]
minutes = duration and duration / 60
puts minutes # imprime 300
Duração em minutos II

24. O operador = tem maior
precedência que o
operador and

25. O que o Ruby vê
duration = song[:duration]
(minutes = duration) and (duration / 60)

26. Evitando surpresas
Não use and e or!

27. Gotcha #3
Constantes podem não ser
constantes

28. Definindo constantes
Ruby considerada constantes “nomes” que
começam com letra maiúscula.

29. Logo
2.3.0 :001 > defined? String
=> “constant”

30. Mas…
2.3.0 :001 > String = ‘Nelson’
(irb):2: warning: already initialized constant String
(irb):1: warning: previous definition of String was
here
=> “Nelson”
2.3.0 :001 > puts String
Nelson
=> nil

31. A pegadinha
Em Ruby constantes são referências para
objetos e por isso podem ser alteradas.

32. Evitando surpresas
module CardTypes
VISA = ‘visa’.freeze
MASTERCARD = ‘mastercard’.freeze
end
CardTypes.freeze

33. Evitando surpresas
# Para arrays precisamos dar freeze
# em todos os elementos do mesmo
[‘visa’, ‘mastercard’].map(&:freeze).freeze!

34. Gotcha #4
Blocks, procs e lambdas

35. Blocks
10.times { puts ‘A lot of strings’ }
10.times do |number|
puts “My number is #{number}”
end

36. Blocks
def get_request(url)
uri = URI(url)
response = Net::HTTP.get_response(uri)
return response unless block_given?
yield(response)
end
get_request(url) do |response|
puts response.body
end

37. Blocks

38. Procs
proc { puts ‘Hello world’ }
Proc.new { puts ‘Hello world’ }

39. Procs
p = Proc.new do |name|
puts “Hello #{name}”
end
p.call # imprime “Hello “

40. A pegadinha
def my_method
proc = Proc.new { return “from proc” }
return “from method”
end
puts my_method # imprime “from proc”

41. Lambdas
-> { puts ‘Hello world’ }
lambda { puts ‘Hello world’ }

42. Lambdas
l = lambda do |name|
puts “Hello #{name}”
end
l.call # Erro!

43. A pegadinha
def my_method
lam = lambda { return “from proc” }
return “from method”
end
puts my_method # imprime “from method”

44. Resumão!

45. Extras

46. Dúvidas?

47. Referências
• http://www.tutorialspoint.com/ruby/ruby_variables.htm
• http://awaxman11.github.io/blog/2013/08/05/what-is-the-difference-between-a-block/
• https://rubymonk.com/learning/books/4-ruby-primer-ascent/chapters/18-blocks/lessons/
64-blocks-procs-lambdas
• http://www.eriktrautman.com/posts/ruby-explained-blocks-procs-and-lambdas-aka-
closures
• https://blog.newrelic.com/2015/04/30/weird-ruby-part-4-code-pods/
• http://blog.jayfields.com/2006/12/ruby-constant-values.html
• http://www.informit.com/articles/article.aspx?p=2251208&seqNum=4
• http://rubylearning.com/blog/2010/09/27/almost-everything-is-an-object-and-everything-
is-almost-an-object/

48. Referências
• blog.elpassion.com/ruby-gotchas/
• http://phrogz.net/programmingruby/tut_expressions.html
• https://github.com/bbatsov/ruby-style-guide
• https://www.ruby-lang.org/en/documentation/ruby-from-other-languages/
• http://www.tutorialspoint.com/ruby/ruby_operators.htm
• https://blog.engineyard.com/2009/3-ruby-quirks-you-have-to-love
• http://stackoverflow.com/questions/372652/what-are-the-ruby-gotchas-
a-newbie-should-be-warned-about

49. Obrigado