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Catch and Throw in Ruby
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Aliaksandr Lomau
July 18, 2018
Technology
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Catch and Throw in Ruby
Rubizza Camp Fire, July 2018
Aliaksandr Lomau
July 18, 2018
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Transcript
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Alialksandr Lomau VETERANT EL “CAPITAN” DEPLOY https://speakerdeck.com/allomov https://twitter.com/code1n
They can be everywhere!
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These Pokemons Are ...
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Variable is not initialized
Variable is not initialized Wrong argument type
Variable is not initialized Wrong argument type File does not
exist
Variable is not initialized Wrong argument type File does not
exist Not enough memory
Variable is not initialized Wrong argument type File does not
exist Not enough memory water pokemon is definitely a memory leak
Ruby == Minefield
Ruby == Minefield
Catche Pokemon with Pokeball
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== Exception Class
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rescue SomeError => e # ... end rescue
rescue SomeError, SomeOtherError => e # ... end multiple rescue
rescue SomeError => e # ... rescue SomeOtherError => e
# ... end stacking rescue
rescue rescue # ... end # is equivalent to: rescue
StandardError # ... end
rescue
rescue rescue Exception => e # ... end
rescue rescue => error # ... end # is equivalent
to: rescue StandardError => error # ... end
rescue begin raise "Timeout while reading from socket" rescue errors_with_message(/socket/)
puts "Ignoring socket error" end
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
raise raise(exception_class_or_object, message, backtrace)
raise raise # is equivalent to: raise RuntimeError
raise raise 'An error has occured.' # is equivalent to
: raise RuntimeError, 'An error has occured.'
raise raise RuntimeError, 'An error has occured.' # is equivalent
to : raise RuntimeError.new('An error has occured.')
raise raise RuntimeError, 'An error' # is equivalent to :
raise RuntimeError, 'An error', caller(0)
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
global variable •$! •$ERROR_INFO note: set it to nil to
rescue exception
ensure begin # do something raise 'An error has occured.'
rescue => e puts 'I am rescued.' ensure puts 'This code always is executed.' end
retry tries = 0 begin tries += 1 puts "Trying
#{tries}..." raise "Didn't work" rescue retry if tries < 3 puts "I give up" end
else begin yield rescue puts "Only on error" else puts
"Only on success" ensure puts "Always executed" end
• 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
Benchmarks
Circuit Breaker pattern
Anti-Patterns • Exceptions controlled flow • rescue nil
What to do with errors? • handle them • send
emails with them • send them to error report system • errbit • pappertrail • elk • … etc.
Alternatives • Callbacks on fails (JavaScript) • Promises (JavaScript) •
Returning codes (golang)
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To Know More
throw "End"