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parse errors when testing for undefined exceptions

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Alan Knowles

22 years ago

This is a simple example of why making a parse error out of undefined
Exception types is going to be very problematic.

function test($a) {

if (!extension_exists('sqlite')) {
return;
}
try {
SQLite::query($a);

// parse error!!! - if we dont have sqlite, we dont have SQLite
exception!

} catch(SQLite_Exception $e) {

echo "problem with query";
return;
}
}


This has a big knock on effect that we can not lazy load Exception
definitions, even if they are only used in Exceptional situations. (its
pretty much the same issue as instanceof - forcing the loading of code,
that may never be used, except to test it's non-existance.)

Regards
Alan

Alan Knowles

22 years ago

aghh.. - another crap example:

The priciple it was try to make was that

....
require_once 'MyException.php'
throw MyException(....);
....

then trying to catch MyException leads to a parse error when it's
try()'d and not loaded.

Regards
Alan

Alan Knowles wrote:

Alan Knowles

22 years ago

aghh.. - the previous example was crap

The priciple it was try to make was that

....
require_once 'MyException.php'
throw MyException(....);
....

then trying to catch MyException leads to a parse error when it's
try()'d and not loaded. means we cant lazy load any Exceptions, and save
file io/memory etc.

Regards
Alan

Alan Knowles wrote:

Ron Korving

22 years ago

Okay, I agree with you on this one.
Very weird behaviour by the way.. I didn't know about this.

"Alan Knowles" <alan@akbkhome.com> schreef in bericht
news:4135CD4B.6040508@akbkhome.com...

Ron Korving

22 years ago

in your function, you should assume sqlite is present.
before calling any functions, have one of the first actions in your script
(preferably in some file you include always anyway) be a check on the
existance of sqlite.

problem solved?

"Alan Knowles" <alan@akbkhome.com> schreef in bericht
news:4135C8C3.5000705@akbkhome.com...

Marcus Börger

22 years ago

Hello Alan,

juts for the record, you can even __autoload the missing exception class:

php -n -r 'function __autoload($n) { var_dump($n); eval("class $n extends Exception {}"); } try { } catch(ExcetpionXYZ $e) {};'

and besides what should the compiler do? Guess what that exception you specified
might be? That's like expecting functions were present of the not loaded
extension...

regrads
marcus

Wednesday, September 1, 2004, 3:04:03 PM, you wrote:

> This is a simple example of why making a parse error out of undefined
> Exception types is going to be very problematic.

> function test($a) {

>     if (!extension_exists('sqlite')) {
>         return;
>     }
>     try {
>         SQLite::query($a);

>     // parse error!!! - if we dont have sqlite, we dont have SQLite
> exception!

>     } catch(SQLite_Exception $e) {

>         echo "problem with query";
>         return;
>     }
> }

> This has a big knock on effect that we can not lazy load Exception
> definitions, even if they are only used in Exceptional situations. (its
> pretty much the same issue as instanceof - forcing the loading of code,
> that may never be used, except to test it's non-existance.)

> Regards
> Alan

--
Best regards,
Marcus                            mailto:helly@php.net

Alan Knowles

22 years ago

Marcus Boerger wrote:

>Hello Alan,
>
>juts for the record, you can even __autoload the missing exception class:
>
>php -n -r 'function __autoload($n) { var_dump($n); eval("class $n extends Exception {}"); } try { } catch(ExcetpionXYZ $e) {};'
>
>

dont you think this is a really horrible kludge?

>and besides what should the compiler do? Guess what that exception you specified
>might be? That's like expecting functions were present of the not loaded
>extension...
>
>

if (!function_exists("hello_world")) {
....
}

While I can understand there is some language design desire to verify
that a class exists so that you have not done a typo, It goes against
the grain of a runtime language that loads only the components (eg.
classes/extensions) as it needs them.

How about:
try  { } catch ("ClassName" $e) { ..... }
if ($e instanceof "ClassName") {.....}

This would allow you to do only explicit classname testing rather than
class exists and type testing

Regards
Alan

Derick Rethans

22 years ago

On Thu, 2 Sep 2004, Alan Knowles wrote:

> Marcus Boerger wrote:
>
> >Hello Alan,
> >
> >juts for the record, you can even __autoload the missing exception class:
> >
> >php -n -r 'function __autoload($n) { var_dump($n); eval("class $n extends Exception {}"); } try { } catch(ExcetpionXYZ $e) {};'
> >
> >
> dont you think this is a really horrible kludge?

But so are exceptions in the first place ;-)

Derick