Ruby – the difference between Raising Exceptions vs Throwing Exceptions in Ruby

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Ruby has two different exceptions mechanisms: Throw/Catch and Raise/Rescue.

Why do we have two?

When should you use one and not the other?

Best Solution

  • raise, fail, rescue, and ensure handle errors, also known as exceptions
  • throw and catch are control flow

Unlike in other languages, Ruby’s throw and catch are not used for exceptions. Instead, they provide a way to terminate execution early when no further work is needed. (Grimm, 2011)

Terminating a single level of control flow, like a while loop, can be done with a simple return. Terminating many levels of control flow, like a nested loop, can be done with throw.

While the exception mechanism of raise and rescue is great for abandoning execution when things go wrong, it's sometimes nice to be able to jump out of some deeply nested construct during normal processing. This is where catch and throw come in handy. (Thomas and Hunt, 2001)

References

  1. Grimm, Avdi. "Throw, Catch, Raise, Rescue… I’m so Confused!" RubyLearning Blog. N.p., 11 July 2011. Web. 1 Jan. 2012. http://rubylearning.com/blog/2011/07/12/throw-catch-raise-rescue--im-so-confused/.
  2. Thomas, Dave, and Andrew Hunt. "Programming Ruby." : The Pragmatic Programmer's Guide. N.p., 2001. Web. 29 Sept. 2015. http://ruby-doc.com/docs/ProgrammingRuby/html/tut_exceptions.html.