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Re: [Chaos] OO Perl Exceptions (fwd)
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Forwarded message:
> From: Blake Mills <blakem@force.stwing.upenn.edu>
> Subject: Re: [Chaos] OO Perl Exceptions (fwd)
> To: phl@lists.pm.org
> Date: Mon, 15 May 2000 17:40:36 -0400 (EDT)
>
> No comment on the exception handling, but I thought I'd chime in with
> a project that you might find interesting. You mentioned
> HTML::Embperl, but have you tried HTML::Mason? I've been using it for
> quite a while now, and it works great.... http://www.masonhq.com
>
> -Blake
>
>
>
> >
> > Ok. I was referred to this list by 2 of the members of another list (who I
> > also think are members of PLUG). Regardless, I've been a perl developer for
> > a little while, and have done some moderatly large projects using Perl.
> >
> > I've got a background with C and C++, and have found that over and over
> > again, when I talk to non-perl people about the language, I keep hearing
> > myself say things like:
> >
> > "Yes, you can do network programming in Perl."
> > "Yes, you can do Object Oritented programming in Perl."
> > "Yes, you can do Refactoring (XP - Martin Fowler) in Perl."
> >
> > Well, I've done all these things in other languages and in Perl. One thing
> > I've been working on lately is taking a design for an application server
> > work-alike and building it into a generic re-useable peice of software so
> > other groups can use it. You can get this [Pas - Perl Application Server]
> > at:
> >
> > http://www.bgw.org/projects/pas2/
> >
> > Right now, I'm using it where I work to build a prototype website. We used
> > an older generation of the same design to do a large ecommerce site, and
> > had alot of success [good performance, fast development] with it. We used
> > Apache/mod_perl and HTML::Embperl against Oracle.
> >
> > I'm trying to make the software/code look more and more OO as I go along,
> > trying to use good programming techniques, yadda yadda yadda.
> >
> > We used Perl's exception handling (die, and if $@) in the original
> > application, but it wasn't very good at recovery - only catching and
> > reporting that there was an error -- and it worked very well. Having
> > come from a C++ background, being able to identify types of exceptions
> > to implement recovery was alot easier when it is an object instead of
> > just a string (or other basic type). I also work with alot of Java
> > developers who I just taught a Perl class to -- I want them to be able
> > to look at the Perl code and be able to grok as much of what's going on
> > as possible.
> >
> > Ok, whith all that background, here's the original series of replies that
> > I sent out to the other lists...
> >
> >
> > Thanks for hearing me out.
> > Kyle R. Burton
> >
> >
> >
> > ---------- Forwarded message ----------
> > Date: Mon, 15 May 2000 14:16:55 -0400 (EDT)
> > From: Kyle Burton <mortis@voicenet.com>
> > Reply-To: chaos@neverlight.com
> > To: chaos@neverlight.com
> > Subject: Re: [Chaos] OO Perl Exceptions
> >
> > Thanks, I just subscribed to that list...I'm going to lurk for a while
> > before I start posting stuff like this.
> >
> > I've already implemented this stuff, and decided on this syntax for now:
> >
> > try {
> > my $base = new Pas::Base;
> > throw new Pas::Exception('Test Exception.');
> > };
> >
> > catch(qw(Pas::Exception e)) and eval {
> > print 'caught: ',$e,"\n";
> > print 'caught: ',$e->error(),"\n";
> > print $e->stacktrace(),"\n";
> > };
> >
> > catch() and eval {
> > print 'caught unknown: ',$@,"\n";
> > }
> >
> > Not quite as clean as what I was shooting for, but it works out to be
> > close enough...
> >
> >
> > k
> >
> > ------------------------------------------------------------------------------
> > The nice thing about Windows is - It does not just crash, it displays a dialog
> > box and lets you press 'OK' first.
> > -- (Arno Schaefer's .sig)
> > mortis@voicenet.com http://www.voicenet.com/~mortis
> > ------------------------------------------------------------------------------
> >
> > On Mon, 15 May 2000, Nicolai Rosen wrote:
> >
> > > Why don't you post it to philly perl mongers? Or if you don't want to
> > > subscribe (it's really only a few messages a week), I can post it for you.
> > >
> > > On Mon, 15 May 2000, Kyle Burton wrote:
> > > > Like other languages (C++, and Java), developers are used to the convienience
> > > > of exception handlers. I know from Perl's fast and looseness, that we
> > > > can't enforce everything at compile time, but...I've been developing
> > > > largish applications in Perl for a little while now, and have used Perl's
> > > > exception handling (eval is try, die is throw, and if($@) is catch) and
> > > > found it to be quite serviceable -- after having used C++'s exception
> > > > handling system for quite some time now.
> > > >
> > > > In the development of the the architecture of Pas (the application server
> > > > work-alike) that I've been building, I decided to create a method called
> > > > throw() on one the base class, so things now can look like this:
> > > >
> > > > unless($condition_to_continue_life) {
> > > > $self->throw("Error, can't continue life\n");
> > > > }
> > > >
> > > > which is just ducky. Looks clean, and inside of throw(), the base class
> > > > uses perl's built-in caller() function to build a stack trace, discover
> > > > who (which module/package) threw the exception, and even at what line number.
> > > >
> > > > Most excellent.
> > > >
> > > > My mind wandered this weekend, and I thought about how the utility of this
> > > > was nice to have, would extension of this concept be a good thing? Should
> > > > I look into bringing this closer to the exception handling of the other
> > > > languages?
> > > >
> > > > I toyed with the idea of using exception objects this morning, and as I
> > > > suspected, you can assign an object to $@, eg:
> > > >
> > > > die new Foo::Exception("You're not going to beleive this, but...");
> > > >
> > > > and when I did the traditional if($@), it had the object in it. So,
> > > > to all the perl developers on this list (and beyond if you feel like
> > > > bringing it up to other people), is this a good way of doing things?
> > > > Should I pursue this path or leave things as they are?
> > > >
> > > > I think it'd be nice and possibly even useful feature to have. Being able
> > > > to key off of the types of exceptions could end up making Perl software
> > > > good at doing error recovery. I imagined code like this:
> > > >
> > > > ...
> > > > unless(open FILE, '</etc/passwd') {
> > > > $self->throw(new Pas::FileException('Error opening file: ',$!,"\n"));
> > > > }
> > > > ...
> > > >
> > > > ...
> > > > eval {
> > > > $foo->crack_passwords();
> > > > };
> > > >
> > > > if($self->catch(Pas::FileException)) {
> > > > print 'Caught FileException: ',$self->exception()->as_string(),"\n";
> > > > exit 0;
> > > > }
> > > > $self->rethrow(); # throw if uncaught...
> > > >
> > > > # equivalent of catch all...
> > > > # if($@) {
> > > > # die $@;
> > > > # }
> > > >
> > > >
> > > > what's the opinion of this group? Is this a symantic waste, or am I
> > > > on to somthing here?
> > > >
> > > > k
> > > >
> > > > ------------------------------------------------------------------------------
> > > > The nice thing about Windows is - It does not just crash, it displays a dialog
> > > > box and lets you press 'OK' first.
> > > > -- (Arno Schaefer's .sig)
> > > > mortis@voicenet.com http://www.voicenet.com/~mortis
> > > > ------------------------------------------------------------------------------
> > > >
> > >
> > > Nicolai Rosen
> > > nick@netaxs.com
> > > Earthstation/Netaxs
> > > http://laktar.dyndns.org/
> > > http://www.netaxs.com/~nick/
> > >
> > >
> > >
> >
> >
> >
> >
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> >
>
>
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