I'd like to figure out how to get mixins up and running under
CGI::Prototype. I think I understand the technical aspects of
Class::Prototyped well enough to pull it off, but I have design questions
that I'd like feedback on. Assuming all goes well, I'd be happy to
contribute a CGI::Prototype::Mixin module to CPAN if I can get it that
generalized. Let me start with three scenarios I'd like to be able to
address and the issues I see:

1. We have at least two applications that have pages that allow users to
upload files. The page is pretty similar in both applications with only a
few application specific things, like the table it's using and an extra
field. What I'd like to do is create an abstract page class for the file
upload page and then implement it with concrete page classes within the
applications themselves, overriding necessary methods to customize. I have
actually done this in the past by not giving the abstract class a base class
and using multiple inheritance in the concrete class like so:

use base qw( Abstract::Page::Class My::App );

And that mostly works, but I'm knew that it could cause problems down the
line and after only a few months I found a scenario where it breaks: under
mod_perl, if I use the mixin page for more than one concrete page class in
my application and use Apache::Reload to reload the concrete page classes, I
get errors with whichever concrete page class is reloaded second. I don't
remember exactly what the error is, but I can look into it if anyone is
interested. Cracking plugability for this example is most important for me
because we actually have two more page types that we need to be able to do
this with and right now they're just duplicated in multiple projects.

2. I would like to create a pluggable diagnostics module that I could stick
in front of my app module to override core CGI::P methods at strategic
locations to capture performance data.

3. We currently have two different validation methodologies and I'm not sure
how soon we'll be picking one or the other to standardize on. I'd like to
create two separate mixin classes so I can choose the validation
functionality to use. I know I could make this work with something like a
Strategy pattern, defining two different validation classes with the same
interface and telling the app which one to use, but if I can get the first
two examples working, this could easily come along for the ride.

The basics of this from a technical perspective should be pretty straight
forward, right? I just need to take the mixin class and manipulate it's
parent and the parent of the class that I want to inherit from it, right?

The complicated part, and perhaps this doesn't have an easy answer, is what
it I want to insert more than one mixin? What if, for example,
CGI::Prototype::Hidden became a mixin, as Randal proposed some time ago (did
I understand that correctly?) and I also have an authentication mixin I'd
like to use. The problem is that, as a developer, I know the interfaces of
the two mixins and what they do, but I don't want to have to look at the
internals of each one to know if I need to put CGI::Prototype::Hidden
infront of CGI::Prototype::Mixin::Auth or vice versa. Is this actually a
connundrum or am I overanalyzing this? Any feedback or ideas would be



Andrew Gianni - Lead Programmer Analyst
University at Buffalo, State University of New York
Computing and Information Technology / Administrative Computing Services
215 MFAC, Ellicott Complex, Buffalo, NY 14261-0026
716.645.5332 - AIM: andrewsgianni - http://www.newkenmore.com/agianni

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