On Apr 12, 2004, at 8:50 AM, George Schlossnagle wrote:
On Apr 12, 2004, at 11:42 AM, Sterling Hughes wrote:
I like OO (*), and I think warnings (non-fatal errors) as exceptions are a stupid idea. Does that count? ;-)
Exceptions in languages like Java are used explicitly to catch fatal errors, not to catch basic errors.
If 'languages like Java' means languages designed for OO, then this is not true. Python throws exceptions for almost everything (KeyError, for example). Even Java throws exceptions (java.sql.Exception) for things like failed database connections which are warnings in PHP.
Languages like Java doesn't mean languages designed for OO, but languages closely adhering to the OO model that PHP uses, Java being the language that can most easily be called the parent of our current model - although I do keep Python in this context even after your KeyError example. The triviality of an exception doesn't make exceptions themselves less severe. Whether or not a KeyError is warranted as an E_ERROR, doesn't in fact change that a KeyError will bump you firmly out of your control flow branch, and make you handle an error condition. In PHP, E_WARNINGs may be misused (that's a discussion for another time, i think); but the fact remains, they do not end your current control flow branch. Changing E_WARNING's to errors catchable by try{}catch{} will not only break BC, but will not make sense for a large number of warnings currently thrown for PHP and lead to the same inconsistencies.
John has gone ahead and committed a perfect example of where exceptions just mess things up. In the tidy extension if you try and set an unknown configuration option it throws an exception. This is not by any stretch of the imagination an unrecoverable error, but rather a simple failure. Yet, if you use tidy in a script, and it is not within a try {} catch {} block your script execution will be terminated because the configuration option could not be resolved. This is much less than desirable and probably confusing for someone who doesn't understand what an exception or why he should care.
You might argue that python or java would throw an exception in this case. For the majority of the java standard library and python code i have found this the opposite, however, even conceding that, PHP should never do this. We have the concept of warnings, in our world an error of this type does *not* terminate script execution. There are even less severe usages of warnings throughout the PHP source code, and there is no reason to convert them to exceptions. And if you don't, you still have the same inconsistencies.
Java and Python both use a mix of philosophies, and indeed there is no complete consensus. However, in my experience and the books that I've read on the subject, the general thought is:
a) throw specific exceptions, not just a "tidy_exception." PHP would need to add a library of built-in exceptions to make this even remotely useful. this is not feasible to do at RC1.66666667
b) don't throw exceptions except when truly exceptional. a function failing is usually not an exception, but rather signified by failure. The exception to this is when using constructors that contain logic (considered bad practice by many btw), and overloading. In these cases exceptions are used in leu of a better solution. This brings us back to KeyError - KeyError is only thrown when overloading is used:
names = ["barney", "fred", "wilma"]
print names["betty"] # throws an exception
print names.get("betty") # returns NoneMost of the exceptions i've found when using both these languages happen on something that maps to something more severe than a configuration option not being found. YMMV.
-Sterling
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