Refactoring Proposal: Enhanced Plugin Architecture

Motivation

The current plugin mechanism don't allow the posibility to have OO-styled plugins wihout ugly hacks from the plugin side, as the handlers are registered by name (ie: using the TWiki::Plugins::PluginName::Handlername style), which prevent OO-Styled plugins from receiving the $self reference as the first parameter.

Description

Modify the way the plugin handlers are registered and applied to allow OO-plugins to register their handlers without any ugly hack.

-- RafaelAlvarez - 01 Jul 2005

Impact and Available Solutions

Implementation

Here is the patch against DEVELOP 4483

Index: lib/TWiki/Plugins.pm
===================================================================
--- lib/TWiki/Plugins.pm   (revision 4483)
+++ lib/TWiki/Plugins.pm   (working copy)
@@ -311,12 +311,12 @@
     my $handlerName = shift;
 
     my $status;
-    foreach my $handler ( @{$this->{registeredHandlers}{$handlerName}} ) {
+    foreach my $plugin ( @{$this->{registeredHandlers}{$handlerName}} ) {
         # Set the value of $SESSION for this call stack
         local $SESSION = $this->{session};
         # apply handler on the remaining list of args
         no strict 'refs';
-        $status = &$handler;
+        my $status=$plugin->invoke($handlerName,@_);
         use strict 'refs';
         if( $status && $onlyOnceHandlers{$handlerName} ) {
             return $status;
Index: lib/TWiki/Plugin.pm
===================================================================
--- lib/TWiki/Plugin.pm   (revision 4483)
+++ lib/TWiki/Plugin.pm   (working copy)
@@ -205,7 +205,7 @@
     foreach my $h ( @registrableHandlers ) {
         my $sub = $p.'::'.$h;
         if( defined( &$sub )) {
-            push( @{$plugins->{registeredHandlers}{$h}}, $sub );
+            push( @{$plugins->{registeredHandlers}{$h}}, $this );
             if( $deprecated{$h} ) {
                 $this->{session}->writeWarning
                   ( $this->{name}.' defines deprecated '.$h );
@@ -214,6 +214,17 @@
     }
 }
 
+# Invoke a handler
+sub invoke {  
+   my $this=shift;
+    my $handlerName=shift;
+   my $handler = 'TWiki::Plugins::' . $this->{name}.'::'.$handlerName;
+   no strict 'refs';
+   my $status=&$handler;
+   use strict 'refs';
+   return $status;
+}
+
 # Get the version number of the specified plugin.
 # SMELL: may die if the plugin doesn't compile
 sub getVersion {

The key change is to register plugin under each handler it has, and to move the responsability to invoke the handler from PluginsDotPm to PluginDotPm. That way, subclases of PluginDotPm can override registerHandlers and invoke in any way they need them to be.

A nice "side effect" of the DakarRelease architecture is that the current PluginDotPm can serve as a wrapper for old-styled plugins.

-- RafaelAlvarez - 01 Jul 2005

Commited on v4484.

-- RafaelAlvarez - 01 Jul 2005

Discussion

Already merged, with more than 3 years in production, and counting

I updated the form, but as the ChangeProposalForm changed, the new data is being displayed.

-- RafaelAlvarez - 08 Aug 2008