Cookbooks
Ruby
Chapter 5. Good Coding Practices
Handling errors

Ruby:
Handling errors

How to:

Ruby uses begin, rescue, ensure, and end to handle errors. You wrap the risky code in begin and end. If an error occurs, rescue kicks in.

begin
  # Risky code goes here.
  puts 10 / 0
rescue ZeroDivisionError => e
  puts "Oops! You can't do that: #{e.message}"
ensure
  puts "This always runs, error or not."
end

Sample Output:

Oops! You can't do that: divided by 0
This always runs, error or not.

Deep Dive

Historically, error handling in programming languages has evolved significantly, with early languages often having crude or non-existent mechanisms. Ruby’s exception handling is inspired by languages like Python and Smalltalk.

Alternatives to begin-rescue in Ruby include using rescue in method definitions or employing throw and catch for non-standard flow control, though they are not used for typical error handling.

One interesting detail: Ruby’s exceptions are objects (instances of Exception class and its descendants), so you can define custom error classes and do more than just log errors — you can carry rich state around the program for more robust error handling.

See Also

  • The Ruby documentation on exceptions and error handling: ruby-doc.org
  • A detailed guide on Ruby error handling best practices: thoughtbot.com
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