On Tue, 2004-02-17 at 00:24, Hans Lellelid wrote:
> I agree with the basic premise the you want people to actually think
> about the Exceptions they are catching. In general I think apps should
> have their own exceptions and throw only Exceptions derived from those;
> in practice, I'm sure there will be lots of little apps that don't
> really need their own Exception tree and so it's nice to have a base
> Exception class. I don't agree, though, with the idea that if I don't
> know that your application throws YourException that it should by
> default leak through my error handling & come out as a PHP fatal error!
> Perhaps we're thinking of different scenarios for this stuff. I'm
> thinking of examples where I have a framework or system that may include
> 3rd party components to do work. For example, Phing (PHP5 Ant port) can
> use a number of PEAR packages or user-defined classes in its
> buildfiles. It would not be appropriate for any of those pieces of code
> to terminate the build by throwing an Exception that Phing doesn't
> expect (catch). At Phing task is an isolated activity and if a package
> that is used by a task throws any Throwable, it needs to be caught by
> the Phing task and logged so that the build script can continue (or
> abort, if the user has specified that behavior).
If I understand correctly, PHP 5 uses an unchecked exception
implementation (functions are not required to declare what exceptions
they throw). I very much agree that unchecked exceptions are the
preferred way to handle things, however ideally I do not think they
should be the only way. I think there is value in a checked exception
and that being able to define an exception that would not be generically
caught by a "catch (Exception $e)" is a good thing. In fact *I* think
using a catch all should generate a compiler warning. ;) Instead I
think exceptions that are not specifically handled should pass up
through the code and into the PHP engine. There they can be caught and
the application can handle them like any other error through
set_error_handler(). How is that any less useful than "catch (Exception
$e) {echo $e->getMessage()}"? In fact, I think it is more useful
because it more appropriately reflects the context that the error is
being handled in; something has gone terribly wrong and I don't know
what to do to fix it. Clearly the programmer is not handling these
exceptions explicitly in their code. Additionally, the error_handler
prototype can be passed the exception object so that the information is
available.
To me exceptions are useful for one reason: context. First of all they
hold more flexibility over trigger_error(). By creating custom
Exception classes (either by extending the Exception class or making a
new base exception class) you can provide additional context about the
error. In languages that have exceptions I never extend the default
classes unless I find it necessary to do so. For example, if I can
handle all my exceptions using the default classes in Java I will. I
see a lot of discussion here of ways to let people use catch all
statements, not handle exceptions, group exceptions into certain
keyholes, etc. To me this is a bad thing and something that is done all
too often with exceptions and only causes problems. Often it is a
result of exceptions being used in-appropriately in the fist place.
All that being said, I'll say again that I am against complicating
exceptions any further in PHP. In fact the more I think about it I
become convinced PHP should at least not require exceptions be used in
the same way it does not force programmers to write OO code. Part of
why I love PHP is its simplicity and similarity to C. I am thoroughly
enjoying the OO additions to PHP and lately have been taking great
advantage of it. Conversely, I don't think the majority of PHP users
use or want to use classes, much less want to learn about using
exceptions properly.
Here are some resources a quick search turned up that might be useful in
explaining my thoughts this time:
General Exception stuff:
http://c2.com/cgi/wiki?UseExceptionsInsteadOfErrorValues
This is a great resource, some of the links off this page are also
very useful.
Java based resources, obvious differences should be kept in mind:
http://www.onjava.com/pub/a/onjava/2003/11/19/exceptions.html
Exception "best practices" in Java.
http://www.hutteman.com/weblog/2003/08/31-118.html
A good description of the importance of using unchecked exceptions.
http://www.darrenhobbs.com/archives/000411.html
He has a great perspective on checked exceptions.
http://www.soletta.com/categories/javaEtc/2003/08/27.html#a324
Just another perspective to ponder. :)
Regards,
Adam
--
Adam Bregenzer
[EMAIL PROTECTED]
http://adam.bregenzer.net/
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