PHP5: Exceptions must valid objects that are derived from class Exception?

I am prototyping on a PHP5 application using PEAR and I ran into a
strange error.

if (PEAR::isError($mReturn)) {
throw $mReturn;
}

PEAR is not configured to return exceptions instead of PEAR Errors and
the above code will generate the following error if $mReturn is a PEAR
Error.

PHP Fatal error: Exceptions must valid objects that are derived from
class Exception in E:\PHPSource\PHPFTP\Source\include\db.inc.php on
line 226

Why must I use the built in exception class? The explantion in release
notes for PHPb4 is that it allows a general catch(Exception $e)
statement to catch all exceptions.

Isn't that up to the developer to deal with it?

/Erik

Markus Fischer wrote:

The catch-all helps catching any type of exception, _given that_ it
is derived from class Exception. The motivation behind it, and this
makes sense to me, I'm pro this behaviour, is, that this way the
interface of the Exception class is well defined. You can always
count that you have the methods getMessage, getCode, getFile,
getTraceAsString, etc. Which is IMO good.

- Markus

With this behavior you force the developer to use the exception class.
You cannot use your own class because PHP will trigger an error if you do.

However, you can of course extend the exception class with your own
class, but you cannot replace the default methods (getMessage etc) since
they are final.

I don't like this, since you are forced to use the built in exception
class which also has final methods. Where has the feeling of freedom gone?

/Erik