Re: Handling invalid objects

["Jeffrey R. Carter" <spam.not.jrcarter@acm.not.spam.org>]

Brian May wrote:
> 
> item &find_item(...) {
>      
>      ... search for item ...
> 
>      if (found) {
>         return item;
>      } else {
>         return ????;
>      }
> }
> 
> The ideal solution would be exceptions, but the students haven't been
> taught exceptions yet when conducting this exercise.

No, exceptions are not ideal. Such a function may often be used in contexts 
where not finding a match is more common than finding one; the former case is 
not exceptional.

Consider a program like grep. It applies a regular-expression-matching function 
to every line in a file. It's quite common for > 80% of the matches to fail; 
that is not an exceptional situation. Using an exception to indicate no match 
would be incorrect.

Booch made this fundamental error in the regular expression matcher in his 
components book.

> Another solution would be to change the API to return a struct value,
> but students are told they cannot change the API.

Then what the student has is an incorrect specification that cannot be implemented.

-- 
Jeff Carter
"From this day on, the official language of San Marcos will be Swedish."
Bananas
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