Catch and Throw in Ruby

Rubizza Camp Fire, July 2018

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"