This document contains code snippets and explanations about exceptions and error handling in Ruby. It discusses topics like raising exceptions, rescuing exceptions, the ensure block, built-in exception classes like RuntimeError, and best practices for using exceptions in code.

2. Alialksandr
Lomau
VETERANT
EL “CAPITAN” DEPLOY
https://speakerdeck.com/allomov
https://twitter.com/code1n

3. They can be everywhere!

8. These Pokemons Are
...

13. Variable is not
initialized

14. Variable is not
initialized
Wrong argument
type

15. Variable is not
initialized
Wrong argument
type
File does
not exist

16. Variable is not
initialized
Wrong argument
type
File does
not exist
Not enough
memory

17. Variable is not
initialized
Wrong argument
type
File does
not exist
Not enough
memory
water pokemon is definitely
a memory leak

18. Ruby == Minefield

19. Ruby == Minefield

20. Catche Pokemon
with Pokeball

22. == Exception Class

24. rescue SomeError => e
# ...
end
rescue

25. rescue SomeError, SomeOtherError => e
# ...
end
multiple rescue

26. rescue SomeError => e
# ...
rescue SomeOtherError => e
# ...
end
stacking rescue

27. rescue
rescue
# ...
end
# is equivalent to:
rescue StandardError
# ...
end

28. rescue

29. rescue
rescue Exception => e
# ...
end

30. rescue
rescue => error
# ...
end
# is equivalent to:
rescue StandardError => error
# ...
end

31. rescue
begin
raise "Timeout while reading from socket"
rescue errors_with_message(/socket/)
puts "Ignoring socket error"
end

32. rescue
def errors_with_message(pattern)
m = Module.new
m.singleton_class.instance_eval do
define_method(:===) do |e|
pattern === e.message
end
end
m
end

33. raise
raise(exception_class_or_object,
message,
backtrace)

34. raise
raise
# is equivalent to:
raise RuntimeError

35. raise
raise 'An error has occured.'
# is equivalent to :
raise RuntimeError, 'An error has occured.'

36. raise
raise RuntimeError, 'An error has occured.'
# is equivalent to :
raise RuntimeError.new('An error has occured.')

37. raise
raise RuntimeError, 'An error'
# is equivalent to :
raise RuntimeError, 'An error', caller(0)

38. caller
2.4.2 :005 > puts caller(0).join("n")
(irb):5:in `irb_binding'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb/workspace.rb:87:in `eval'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb/workspace.rb:87:in `evaluate'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb/context.rb:381:in `evaluate'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb.rb:493:in `block (2 levels) in eval_input'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb.rb:627:in `signal_status'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb.rb:490:in `block in eval_input'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb/ruby-lex.rb:246:in `block (2 levels) in
each_top_level_statement'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb/ruby-lex.rb:232:in `loop'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb/ruby-lex.rb:232:in `block in each_top_level_sta
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb/ruby-lex.rb:231:in `catch'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb/ruby-lex.rb:231:in `each_top_level_statement'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb.rb:489:in `eval_input'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb.rb:430:in `block in run'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb.rb:429:in `catch'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb.rb:429:in `run'
/Users/allomov/.rvm/rubies/ruby-2.4.2/lib/ruby/2.4.0/irb.rb:385:in `start'
/Users/allomov/.rvm/rubies/ruby-2.4.2/bin/irb:11:in `<main>'
=> nil

39. global variable
•$!
•$ERROR_INFO
note: set it to nil to rescue exception

40. ensure
begin
# do something
raise 'An error has occured.'
rescue => e
puts 'I am rescued.'
ensure
puts 'This code always is executed.'
end

41. retry
tries = 0
begin
tries += 1
puts "Trying #{tries}..."
raise "Didn't work"
rescue
retry if tries < 3
puts "I give up"
end

42. else
begin
yield
rescue
puts "Only on error"
else
puts "Only on success"
ensure
puts "Always executed"
end

43. • Use exception when you need
• Wrap exception when re-raising
• Avoid raising during ensure
• Exception is your method interface too
• Classify your exceptions
• Readable exceptional code
• Declare classes for app exception
good points

44. Benchmarks

45. Circuit Breaker pattern

46. Anti-Patterns
• Exceptions controlled flow
• rescue nil

47. What to do with errors?
• handle them
• send emails with them
• send them to error report system
• errbit
• pappertrail
• elk
• … etc.

48. Alternatives
• Callbacks on fails (JavaScript)
• Promises (JavaScript)
• Returning codes (golang)

52. To Know More

53. throw "End"