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The code example is not convincing at all. Obviously a single if is much cleaner than a single try/catch block but that is not the comparison. The if needs to b

by cjfd 7y ago

The code example is not convincing at all. Obviously a single if is much cleaner than a single try/catch block but that is not the comparison. The if needs to be replicated N times for every N things that could fail and that are calling each other in a potentially deep call hierarchy. The try/catch block only needs to occur once at a level that is above all of the N things that might fail.

dllthomas 7y ago
In my experience, on the web there are two different kinds of things we might be fetching. Some things are essential to the page we are rendering, and if they are missing we should 404. Some things are ancillary, and if they are missing we should render a stub in their place. E.g., saying that a comment is from "deleted user". Exceptions are a good fit for the former, where we want to unify every failure. They are a poor choice for the other case, where we want to treat each failure special. Which case a given fetch represents is a choice that should be driven by the fetcher.
- cjfd 7y ago
  Sure, it depends on the situation. In the case you outline, there could also be room for an auxiliary function like fetch_alternatives({ preferred_resouce, second_best_resource , third_best_resource}) that would fetch them in until one can actually be obtained and throw an exception if all of them fail. Not that I am married to exceptions or anything. One should just use what is best in the situation that one is in. Actually, I think articles that claim that one language construct is better than some other language construct are quite silly. It mostly depends on the situation. Though, there also may be language constructs that are best left off deprecated, depending the language that you are using.
- AstralStorm 7y ago
  Why are they a poor choice for the latter? They have a type, make it say MissingUserException and the special place can handle it in a special way. Ensure it is a subclass of some general exception type you also handle elsewhere and you're good. Often people throw generic exceptions instead of using the type system.
  - dllthomas 7y ago
    In the latter case you will often want to pass "data or the fact the data was missing" along to other functions. With a result value (of whatever form) that's trivial. With exceptions, it's certainly plenty doable but it's messy.
ravenstine 7y ago
That doesn't always make sense when you're dealing with a generic exception class. What you are assuming is that a try-catch block higher up in the hierarchy can handle a RecordNotFound exception for all its descendants, but that's not necessarily going to be the case. It's basically the inheritance problem in object-oriented programming, but in reverse. This is why I'm in favor if exceptions for non-broken states to not be a thing or at least be optional. Making a request to an API or database and getting a successful response returning no data(or a message that says data wasn't found) means that the code and the services in the system are actually working correctly, and throwing an exception is treating the situation like a code problem when it could(and often is) simply be a data problem, which is common and often expected.
- cjfd 7y ago
  Yes, the try/catch block is better if the catch block can handle exceptions for all its descendants. As always in programming YMMV and this is sometimes true and sometimes it is not and when it is not it is better not to throw an exception. I agree that a database API should not itself throw an error if an empty result set is found. It may throw an error if there is an SQL error, though, and really should. When one gets an empty result set where this should not happen, for instance because a row was just inserted and one is in a transaction, the user code could throw an exception instead. Making exceptions optional is something that I have indeed done in the past because some uses of the code could benefit from exceptions while other uses did not so much.

by cjfd 7y ago

dllthomas 7y ago

In my experience, on the web there are two different kinds of things we might be fetching. Some things are essential to the page we are rendering, and if they are missing we should 404. Some things are ancillary, and if they are missing we should render a stub in their place. E.g., saying that a comment is from "deleted user". Exceptions are a good fit for the former, where we want to unify every failure. They are a poor choice for the other case, where we want to treat each failure special. Which case a given fetch represents is a choice that should be driven by the fetcher.

cjfd 7y ago
Sure, it depends on the situation. In the case you outline, there could also be room for an auxiliary function like fetch_alternatives({ preferred_resouce, second_best_resource , third_best_resource}) that would fetch them in until one can actually be obtained and throw an exception if all of them fail. Not that I am married to exceptions or anything. One should just use what is best in the situation that one is in. Actually, I think articles that claim that one language construct is better than some other language construct are quite silly. It mostly depends on the situation. Though, there also may be language constructs that are best left off deprecated, depending the language that you are using.
AstralStorm 7y ago
Why are they a poor choice for the latter? They have a type, make it say MissingUserException and the special place can handle it in a special way. Ensure it is a subclass of some general exception type you also handle elsewhere and you're good. Often people throw generic exceptions instead of using the type system.
- dllthomas 7y ago
  In the latter case you will often want to pass "data or the fact the data was missing" along to other functions. With a result value (of whatever form) that's trivial. With exceptions, it's certainly plenty doable but it's messy.

ravenstine 7y ago

That doesn't always make sense when you're dealing with a generic exception class. What you are assuming is that a try-catch block higher up in the hierarchy can handle a RecordNotFound exception for all its descendants, but that's not necessarily going to be the case. It's basically the inheritance problem in object-oriented programming, but in reverse. This is why I'm in favor if exceptions for non-broken states to not be a thing or at least be optional. Making a request to an API or database and getting a successful response returning no data(or a message that says data wasn't found) means that the code and the services in the system are actually working correctly, and throwing an exception is treating the situation like a code problem when it could(and often is) simply be a data problem, which is common and often expected.

cjfd 7y ago
Yes, the try/catch block is better if the catch block can handle exceptions for all its descendants. As always in programming YMMV and this is sometimes true and sometimes it is not and when it is not it is better not to throw an exception. I agree that a database API should not itself throw an error if an empty result set is found. It may throw an error if there is an SQL error, though, and really should. When one gets an empty result set where this should not happen, for instance because a row was just inserted and one is in a transaction, the user code could throw an exception instead. Making exceptions optional is something that I have indeed done in the past because some uses of the code could benefit from exceptions while other uses did not so much.