[htmltmpl] A new plugin provider based on CGI::App's design

[Mark S. <ma...@su...>]

As I worked on a new plugin system for HTML::Template [0], I recycled code from
CGI::Application's new plugin system [1].

As I reflected on this, CGI::Application has developed a nice plugin system
which is easily re-usable on it's own.

It is most similar to Class::Trigger [2], but I think the CGI::App solution is
more advanced for these reasons:

 - We look up the inheritance tree for more callbacks to execute

 - We allow arguments to be passed into the callbacks, customizing how each
   callback can work, and creating clearer, more explicit syntax than passing
   through the object.

 - We have a specific callback ordering, and we expect to soon solve the
   problem of making this ordering to be sufficiently flexible to address
   most plugin needs. 

 - Class::Trigger requires your object be implemented as blessed hashref
   (Gasp!). We could solve this in our implementation by adding a method for
   'installed_callbacks()', which could be trivially overridden if the
   callbacks needed to be stored in the object a different way.

So I would like to move CGI::App's plugin system into it's own module, which
wouldn't change anything from a user's perspective, except perhaps where the
related documentation is located. 

I could see what we have possibly being merged into a future enhanced version
of Class::Trigger, which CGI::App would then have it's own plugin for, to keep 
compatibility with the names we've already established.

 0. http://use.perl.org/~markjugg/journal/26089
 1. http://www.cgi-app.org/?Plugins 
 2. http://search.cpan.org/perldoc?Class::Trigger

Collaborators welcome! Let's keep discussing it on the CGI::App mailing
list and #cgiapp on irc.perl.org.

    Mark

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