Hello-- On Aug 3, 2009, at 12:50 PM, Alpha Blue wrote:
> > Marnen Laibow-Koser wrote: >> Um, WTF? That's where logic is supposed to go. Exception handling >> supplements that logic; it doesn't replace it. >> There are times when it might be necessary (methods that >>> involve rake tasks etc. come to mind) but overall, rescue is >>> something >>> everyone new to rails should learn and implement into their apps. >>> > > I didn't use the right wording here. What I meant was there are > different types of logic to use with your model. In otherwords, for > every method created there are probably 3 people that will do them > completely different but achieve the same result. > > Remember for loops? Which logic is better to do in the model? A for > loop or an each loop? Which is better practice? This is what I was > after. You can go to an extreme on one thing and never use the > simpler > approaches. > >> Many developers (including me!) perhaps don't use exceptions quite as >> often as they should, but I am afraid that you are encouraging the >> opposite extreme -- a style of programming where exceptions are >> used for >> everything. I understand that this is not a great idea for a >> number of >> reasons: it is said to be inefficient and hard to follow and test. >> > > I'm not sure I follow you completely on this particular response. Are > you saying that rescue is a bad thing when you need a routine to > continue moving forward? Or, are you saying that there's another way > (besides rescue) that should be used to do the same thing? I like > rescue. I don't use it for everything but there are some core areas > in > my app that I do use it. > I bring a fair amount of dated knowledge to this -- the "why not use exception handling for everything" answers from the days of C++ and the like. I learned to steer clear of exception handling in cases where I could fairly predict an outcome. Ruby may have a slick implementation of exception handling and certainly does not have the baggage of unwinding through destructors that C++ had, but an exception is a non-local jump, not to be confused with scope exit caused by a flow of control structure. That means someplace things like multiple scopes need to be recognized so stale objects can be marked for garbage collection, etc. Additionally, in the presence of a begin/rescue block, when an exception occurs, the interpreter has to look for the closest scoped exception handling block that declares itself as handling the specific type or generic superset of the exception in question. This means maintaining an ordered searchable list of these scoped blocks, thus taking up memory for a case which is supposed to never happen, right? So here's my way of deciding whether to use exceptions. I ask the questions: "Is the result of this operation predictable?" If yes, then I test for it, and don't use exceptions. "If this operation fails, is there anything I can do about it?" If the answer is no, then I let Rails' rescue_action_in_public take care of things for me and get my exception_notification email. Then I fix the bug. "If this operation fails and there is it important and something I can fix programatically (e.g., would financial data be corrupted or something equally disasterous and will I have information to mitigate the damage)?" If the answer is yes, then I'll use a begin/rescue block. All of this said, there is a reason exception handling is in the language, but it's not (IMO) the one you cite. Exception handling is made to wrap very important operations that simply can't fail without at least an honest retry strategy. You know, like "user stepped on anti-lock brake pedal and braking computer raised an exception." What exceptions were not specifically designed for was to facilitate non- local jumps out of scope. I know there will be disagreement on what I've said here, so I must re- emphasize that my habits with respect to use of exception handling are based on avoidance rooted in a pretty dated technology, C++. Additionally, this is something of a religious issue, where you either hate exceptions to the extreme or see no harm in them and use them liberally. I've put my opinion out here in hopes it will be useful. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk@googlegroups.com To unsubscribe from this group, send email to rubyonrails-talk+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
