# Own exception classes **URL:** \ **Category:** Ruby\ **Created:** [April 15, 2010, 6:30pm UTC](https://www.ruby-forum.com/t/own-exception-classes/187012 "2010-04-15T18:30:45Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![lykos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/b5e925/32.png) [@lykos](https://www.ruby-forum.com/u/lykos)\ **Post date:** [April 15, 2010, 6:30pm UTC](https://www.ruby-forum.com/t/own-exception-classes/187012/1 "2010-04-15T18:30:45Z")
Hi, I’m working at a bigger private project with my brother now and I wanted to ask, in which cases you recommend own exception classes. One possibility would just be to use no own exceptions and just use raise “message”. One other possibility would be to use an own exception class for every situation. What do you recommend? Another small question. This is my first “distributed” private project, so we basically don’t meet very often and just implement our classes and communicate via email sometimes. Are there any tips about this setting or anything that we should pay attention to in order to avoid problems in the future when the project gets bigger and more complicated? Thanks in advance, greetings. Bernhard B. ---
**Author:** ![lykos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/b5e925/32.png) [@lykos](https://www.ruby-forum.com/u/lykos)\ **Post date:** [April 15, 2010, 6:40pm UTC](https://www.ruby-forum.com/t/own-exception-classes/187012/2 "2010-04-15T18:40:15Z")
Hey Bernard, I use this philosophy when designing code with custom exceptions: Only create exceptions that you (or other developers using your code) will rescue from. So if I notice I’m creating exceptions that never get rescued in my own code, and I don’t have a valid reason for why another developer would rescue from it, I blast it. Likewise, I treat: begin … rescue StandardError … end and begin … rescue … end As code smells, and refactor that by creating an exception. Also if you do go down the path of creating custom exceptions, I’ve found that creating exceptions in the form of: class MyError \< StandardError end tends to be the cleanest, but of course your mileage may vary. Here’s a link to a project I’m currently working on that defines it’s own exceptions. > I hope this helps. – Zach M. > **[Simple Chatter | Let's Chat About Life, Family and Womanhood!](https://www.simplechatter.com/)** > > Simple Chatter is a blog site about Family, Motherhood, Womanhood, Self-Help, Overcoming Obstacles, Faith, Finance, Planning/Organizing and Life Coaching. ---
**Author:** ![lykos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/b5e925/32.png) [@lykos](https://www.ruby-forum.com/u/lykos)\ **Post date:** [April 15, 2010, 6:46pm UTC](https://www.ruby-forum.com/t/own-exception-classes/187012/3 "2010-04-15T18:46:09Z")
On Thu, Apr 15, 2010 at 10:30 AM, Bernhard B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > I’m working at a bigger private project with my brother now and I wanted > to ask, in which cases you recommend own exception classes. > > One possibility would just be to use no own exceptions and just use > raise “message”. One other possibility would be to use an own exception > class for every situation. What do you recommend? I would use exception classes for all but trivial cases. I sometimes use raise “message” for small projects as a placeholder for a better error message or for debugging, but that’s about it… since the whole idea of exceptions is to catch them, it is far better to be able to ‘rescue SomeTerribleException =\> e’ than to have to rescue Exception =\> e and have to test the exception string to find out what went wrong (especially since the exception string can easily be changed without thinking about it!) In summary, exception classes. As to your other question, I’ll defer that to those who know better… I just know that version control is your friend. -Jonathan N. ---
**Author:** ![lykos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/b5e925/32.png) [@lykos](https://www.ruby-forum.com/u/lykos)\ **Post date:** [April 15, 2010, 7:52pm UTC](https://www.ruby-forum.com/t/own-exception-classes/187012/4 "2010-04-15T19:52:12Z")
Zach M. wrote: > Hey Bernard, > > I use this philosophy when designing code with custom exceptions: Only > create exceptions that you (or other developers using your code) will > rescue from. > > Also if you do go down the path of creating custom exceptions, I’ve > found that creating exceptions in the form of: > > class MyError \< StandardError > end > > tends to be the cleanest, but of course your mileage may vary. Here’s a > link to a project I’m currently working on that defines it’s own > exceptions. > [harvested/lib/harvest/api/base.rb at master · zmoazeni/harvested · GitHub](http://github.com/zmoazeni/harvested/blob/master/lib/harvest/api/base.rb#L23) > > I hope this helps. Thanks a lot, it was really a good idea to ask my question here since this was something I didn’t think about on my own. Creating own classes makes exception handling much more effective, so I think I will do that in most cases. Jonathan N. wrote: > I would use exception classes for all but trivial cases. I sometimes > use raise “message” for small projects as a placeholder for a better > error message or for debugging, but that’s about it… since the whole > idea of exceptions is to catch them, it is far better to be able to > ‘rescue SomeTerribleException =\> e’ than to have to rescue Exception > =\> e and have to test the exception string to find out what went wrong > (especially since the exception string can easily be changed without > thinking about it!) > > In summary, exception classes. Ok, that really sounds logic. Testing for exception strings would be terrible. > As to your other question, I’ll defer that to those who know better… > I just know that version control is your friend. Ok, thanks for that, but we’re already using git and github. Robert D. wrote: > On Thu, Apr 15, 2010 at 6:40 PM, Zach M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > wrote: > > > �class MyError \< StandardError > > �end > > I agree with most you say, but I took the habit to inherit from > > RuntimeError rather than StandardError a long time ago. AAMOF I forgot > > why? Does someone here recall the rationale? Ok, that seems to be the next question. But I think I will inherit from an own parent exception with most exceptions anyway, since it seems to be reasonable to allow rescuing from all own exceptions and then I think it doesn’t really matter which one I’ll choose as the parent of this exception. ---
**Author:** ![lykos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/b5e925/32.png) [@lykos](https://www.ruby-forum.com/u/lykos)\ **Post date:** [April 15, 2010, 7:31pm UTC](https://www.ruby-forum.com/t/own-exception-classes/187012/5 "2010-04-15T19:31:48Z")
On Thu, Apr 15, 2010 at 6:40 PM, Zach M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > class MyError \< StandardError > end > I agree with most you say, but I took the habit to inherit from > RuntimeError rather than StandardError a long time ago. AAMOF I forgot > why? Does someone here recall the rationale? Cheers R. ---
**Author:** ![lykos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/b5e925/32.png) [@lykos](https://www.ruby-forum.com/u/lykos)\ **Post date:** [April 15, 2010, 8:30pm UTC](https://www.ruby-forum.com/t/own-exception-classes/187012/6 "2010-04-15T20:30:22Z")
The problem (IIRC) with extending from Exception instead of StandardError is that a plain ‘rescue’ statement will not catch bare Exceptions, it catches StandardError (or is it RuntimeError?) by default. To catch Exception (or descended classes), you need to specify ‘rescue Exception’. But it’s a bit easier just to extend from StandardError or RuntimeError, both of which are caught by a bare rescue statement. -Jonathan N. ---
**Author:** ![lykos](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/b5e925/32.png) [@lykos](https://www.ruby-forum.com/u/lykos)\ **Post date:** [April 15, 2010, 7:57pm UTC](https://www.ruby-forum.com/t/own-exception-classes/187012/7 "2010-04-15T19:57:00Z")
On Apr 15, 2010, at 1:31 PM, Robert D. wrote: > I agree with most you say, but I took the habit to inherit from > RuntimeError rather than StandardError a long time ago. AAMOF I forgot > why? Does someone here recall the rationale? I’d be interested in hearing the rationale too. I actually forget my argument for using StandardError, I only remember running into issues (that I also don’t remember) doing class MyError \< Exception … end I’ve seen smarter devs than me using StandardError, so I’ve been in mostly emulation mode 🙂