|
Nemanja Trifunovic wrote: But in general, not finding a value in a collection is not an exceptional event
I like to think of it in "design by contract" terms. If a method cannot fulfil its contract then it must cause an exception (or generically, a program fault) otherwise it should not.
I think the "exceptions are for exceptional cases" mantra is too vague. We might envisage a method where a rare event occurs but the method's spec is designed to account for that. In that case it should not cause an exception, even though the event was "exceptional."
You could put it this way: "Exceptions imply exceptional cases (because errors are exceptional) but not vice-versa."
Kevin
|
|
|
|
|
Kevin McFarlane wrote: I like to think of it in "design by contract" terms.
Can I smell Eiffel here  ?
Seriously, you are right - we just have a terminology problem here: by "exceptional" I do not mean "rare" but "unexpected" or "violated the contract".
modified on Monday, August 24, 2009 10:48 AM
|
|
|
|
|
Nemanja Trifunovic wrote: Can I smell Eiffel here Smile ?
Yeah, or Spec# or Code Contracts for .NET 4. Not sure if there's anything which supplies full support in C++ though?
Kevin
|
|
|
|
|
Kevin McFarlane wrote: Not sure if there's anything which supplies full support in C++ though
Nothing built-in, but there are libraries - in fact I remember one published here at CP.
There are some non-standard extensions for DbC in the Digital Mars C++ compiler, and of course D supports it (at least D 1.0, not sure about 2.0)
|
|
|
|
|
I agree with Chris. That is the way to do it!
Throwing an exception is unacceptable since exception should be used for errors. "No result" is not (always) an error condition.
Morale: Use the right tool for the right task.
Bye By(t)e 
|
|
|
|
|
Returning a list is different from returning an object. If my requirements are to return a list, I always return a list (albeit it may be empty). But if I am supposed to return an instance of some one object I usually will return null if I cannot create a valid object hence my vote for null.
WarePhreak
Programmers are tools to convert caffiene to code.
|
|
|
|
|
Yeeesss... but an Exception can tell you why you got nothing useful back.
"Waiter! I can't eat this soup." ...
|
|
|
|
|
If the object is expected then returning a null will force the caller to check the return type and then try to work out why the call failed.
If you think the object might not be found then you should either provide a method to check the object exists or implement a Try... method that returns a boolean success/fail and the object as an out parameter.
|
|
|
|
|
Checking the what a function return is always a good idea: Using exceptions and a try/catch just to avoid check the result is only lazyness (IMO).
However I agree in general that you should provide a way to quick check the result of the operation result i.e. supposing you wrote a function that search one element in a collection I prefer something like the following:
// Search an object and return its position (if found) using pPositionWhereFound.
Bool searchObj ( Oject_t *pList, Oject_t* pObjToSearch, int *pPositionWhereFound );
instead of:
// Search an object and return its position (if found). -1 as return value
// means not found
int searchObj ( Oject_t *pList, Oject_t* pObjToSearch );
in both cases you have to check the returned value but doing:
if ( searchObj( &List, &ObjToSearch, &Position ) )
...
is nicer than:
int iPosition = searchObj( &List, &ObjToSearch );
if ( iPosition != -1 )
...
Bye By(t)e
|
|
|
|
|
Simone Serponi wrote: Checking the what a function return is always a good idea
Yes, but hope that consumers of your code will always check if you return null or valid object is just asking for trouble.
To be honest I prefer bug report with exception message "check_first_if_object_exeists_before_requesting_it_noob" than plain null object exception. It just saves time fixing code (on any side) 
--
"My software never has bugs. It just develops random features."
|
|
|
|
|
deflinek wrote: Yes, but hope that consumers of your code will always check if you return null or valid object is just asking for trouble.
To be honest I prefer bug report with exception message "check_first_if_object_exeists_before_requesting_it_noob" than plain null object exception. It just saves time fixing code (on any side) Cool
As I already told checking function return value is (should be) a must...
Moreover this is the classical thing that is documented into the Reference Manual of the code (thanks to God for DoxyGen) and looking at the documentation before use it is always a good idea.
However, yes, "The mother of noobs is always pregnant", and I'm sure someone will use the function without check the return value. But in this case it is not my fault: Read the documentation first! 
Bye By(t)e
|
|
|
|
|
Member 2053006 wrote: If you think the object might not be found then you should either provide a method to check the object exists or implement a Try... method that returns a boolean success/fail and the object as an out parameter.
Totally agree. I'm a big fan of the TryParse() style methods.
There are some cases where they don't apply so well; e.g., cases where the condition can change between the check and use. A check for a file's existence doesn't mean that the file is still there when you try to open it in the next statement. Sometimes I think TryParse() style methods in these cases can create a false sense of security... OTOH, at least they let you return an intelligible error message for many execution scenarios.
|
|
|
|
|
With the current wording of the question, I throw. An error always gives an exception in my book. However, I don't always consider something missing as an error, only if I expect it to be there. I usually do this:
Foo bar = provider.GetFoo(FooType.Bar);
Foo baz = provider.FindFoo(FooType.Baz);
--
Time you enjoy wasting is not wasted time - Bertrand Russel
|
|
|
|
|
I agree about the "Find", but don't necessarily agree on the "Get". Please see my reply to Nishant above, if my GetTradeData(string tradeID) fails, I would not throw an exception.
FindTradeData(string tradeID) sounds silly.
Cheers,
Vikram. (Proud to have finally cracked a CCC!)
|
|
|
|
|
I like to be consistent. Hence, my GetX(...) and FindX(...) always[1] do what I just described, no exception (sic!)
Vikram A Punathambekar wrote: FindTradeData(string tradeID) sounds silly.
In my book, that's not a valid reason to omit doing anything other than singing in falsetto...
If I expect to find trade data with id tradeID in there, then I definitely consider it to be an error if it's not there, and I would therefore throw.
[1] Off the top of my head at 00.25 AM. My memory might fail, for obvious reasons. 
--
Time you enjoy wasting is not wasted time - Bertrand Russel
|
|
|
|
|
As a side note - I'm not hesitant to use GetOrCreateX(String id) methods if the object needs to manage things on it's own and the caller doesn't care if the X existed before the call or not.
--
Time you enjoy wasting is not wasted time - Bertrand Russel
|
|
|
|
|
I agree. Because it said you were expecting an object to be returned, then if it cant return one that's an exception. If it were a function that may or should probably return an object, then a null would be acceptable. More like a 'not found' (null) vs a 'couldn't load/create object for some other reason like corrupt data'.
|
|
|
|
|
I depends on the situation.
First choice is throw an Exception.
In some cases return an empty collection.
In other cases, return null.
|
|
|
|
|
Yes, it depends on how normal it is to find no result. If it is very very strange, I return an Exception. Otherwise it's usually null, or an empty collection in some cases.
|
|
|
|
|
me too. these days we use the exception handling application block, so i return null after the ExceptionPolicy.HandleException code. that way, if the exception is not rethrown, the method returns null.
|
|
|
|
|
I do 2 & 3, I almost never throw an exception, habit I guess, I certainly test and deal with the empty collection I just consider an exception a worst case scenario.
I have a favourite rant about programming by error, you know try writing to the database and if it throws an exception then there is something wrong, drop wing squawk loudly and run in circles
|
|
|
|
|
If I'm returning a Value type, then I can't return 'null'. If the method is for generics, than I'll use the 'default' keyword, but again, for Reference types, that will still translate to 'null'. At work in a lot a places in the code there is a result code and an out parameter. When returning a list of items, if there are no items then I may return an empty list instead of 'null'. So basically, it depends on the situation and what is being returned.
Should I be more consistent?
|
|
|
|
|
No. You shouldn't. This is the same way (or style?) I do it here.
|
|
|
|
|
I use some agreed upon impossible value if value type is in question, null if reference type and empty collection for collections.
Exception get thrown only if it is really an error, condition that is not checked by program or it comes from the database.
It is consistent regardless of treating different objects differently.
|
|
|
|
|
Much The Same - It depends upon what makes sense to return rather than entrapping myself with some dogmatic formula to which one must adhere.
For example, it is often much more sensible (fool-proof?) to return an empty String in a method that returns a String object, rather than a null - the results of which are therefore always printable. This avoids a later test of the return when something, even if blank, will always be required.
Will this confuse other potential users - isn't that what documentation is for ? ?
"The difference between genius and stupidity is that genius has its limits." - Albert Einstein
"As far as we know, our computer has never had an undetected error." - Weisert
"It's a sad state of affairs, indeed, when you start reading my tag lines for some sort of enlightenment. Sadder still, if that's where you need to find it." - Balboos HaGadol
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
