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+.\" ========================================================================
+.\"
+.IX Title "Template::Plugin::Filter 3"
+.TH Template::Plugin::Filter 3 "2009-07-04" "perl v5.8.7" "User Contributed Perl Documentation"
+.SH "NAME"
+Template::Plugin::Filter \- Base class for plugin filters
+.SH "SYNOPSIS"
+.IX Header "SYNOPSIS"
+.Vb 1
+\& package MyOrg::Template::Plugin::MyFilter;
+.Ve
+.PP
+.Vb 2
+\& use Template::Plugin::Filter;
+\& use base qw( Template::Plugin::Filter );
+.Ve
+.PP
+.Vb 2
+\& sub filter {
+\& my ($self, $text) = @_;
+.Ve
+.PP
+.Vb 1
+\& # ...mungify $text...
+.Ve
+.PP
+.Vb 2
+\& return $text;
+\& }
+.Ve
+.PP
+.Vb 2
+\& # now load it...
+\& [% USE MyFilter %]
+.Ve
+.PP
+.Vb 4
+\& # ...and use the returned object as a filter
+\& [% FILTER $MyFilter %]
+\& ...
+\& [% END %]
+.Ve
+.SH "DESCRIPTION"
+.IX Header "DESCRIPTION"
+This module implements a base class for plugin filters. It hides
+the underlying complexity involved in creating and using filters
+that get defined and made available by loading a plugin.
+.PP
+To use the module, simply create your own plugin module that is
+inherited from the \f(CW\*(C`Template::Plugin::Filter\*(C'\fR class.
+.PP
+.Vb 1
+\& package MyOrg::Template::Plugin::MyFilter;
+.Ve
+.PP
+.Vb 2
+\& use Template::Plugin::Filter;
+\& use base qw( Template::Plugin::Filter );
+.Ve
+.PP
+Then simply define your \f(CW\*(C`filter()\*(C'\fR method. When called, you get
+passed a reference to your plugin object (\f(CW$self\fR) and the text
+to be filtered.
+.PP
+.Vb 2
+\& sub filter {
+\& my ($self, $text) = @_;
+.Ve
+.PP
+.Vb 1
+\& # ...mungify $text...
+.Ve
+.PP
+.Vb 2
+\& return $text;
+\& }
+.Ve
+.PP
+To use your custom plugin, you have to make sure that the Template
+Toolkit knows about your plugin namespace.
+.PP
+.Vb 3
+\& my $tt2 = Template\->new({
+\& PLUGIN_BASE => 'MyOrg::Template::Plugin',
+\& });
+.Ve
+.PP
+Or for individual plugins you can do it like this:
+.PP
+.Vb 5
+\& my $tt2 = Template\->new({
+\& PLUGINS => {
+\& MyFilter => 'MyOrg::Template::Plugin::MyFilter',
+\& },
+\& });
+.Ve
+.PP
+Then you \f(CW\*(C`USE\*(C'\fR your plugin in the normal way.
+.PP
+.Vb 1
+\& [% USE MyFilter %]
+.Ve
+.PP
+The object returned is stored in the variable of the same name,
+\&'\f(CW\*(C`MyFilter\*(C'\fR'. When you come to use it as a \f(CW\*(C`FILTER\*(C'\fR, you should add
+a dollar prefix. This indicates that you want to use the filter
+stored in the variable '\f(CW\*(C`MyFilter\*(C'\fR' rather than the filter named
+\&'\f(CW\*(C`MyFilter\*(C'\fR', which is an entirely different thing (see later for
+information on defining filters by name).
+.PP
+.Vb 3
+\& [% FILTER $MyFilter %]
+\& ...text to be filtered...
+\& [% END %]
+.Ve
+.PP
+You can, of course, assign it to a different variable.
+.PP
+.Vb 1
+\& [% USE blat = MyFilter %]
+.Ve
+.PP
+.Vb 3
+\& [% FILTER $blat %]
+\& ...text to be filtered...
+\& [% END %]
+.Ve
+.PP
+Any configuration parameters passed to the plugin constructor from the
+\&\f(CW\*(C`USE\*(C'\fR directive are stored internally in the object for inspection by
+the \f(CW\*(C`filter()\*(C'\fR method (or indeed any other method). Positional
+arguments are stored as a reference to a list in the \f(CW\*(C`_ARGS\*(C'\fR item while
+named configuration parameters are stored as a reference to a hash
+array in the \f(CW\*(C`_CONFIG\*(C'\fR item.
+.PP
+For example, loading a plugin as shown here:
+.PP
+.Vb 1
+\& [% USE blat = MyFilter 'foo' 'bar' baz = 'blam' %]
+.Ve
+.PP
+would allow the \f(CW\*(C`filter()\*(C'\fR method to do something like this:
+.PP
+.Vb 2
+\& sub filter {
+\& my ($self, $text) = @_;
+.Ve
+.PP
+.Vb 2
+\& my $args = $self\->{ _ARGS }; # [ 'foo', 'bar' ]
+\& my $conf = $self\->{ _CONFIG }; # { baz => 'blam' }
+.Ve
+.PP
+.Vb 1
+\& # ...munge $text...
+.Ve
+.PP
+.Vb 2
+\& return $text;
+\& }
+.Ve
+.PP
+By default, plugins derived from this module will create static
+filters. A static filter is created once when the plugin gets
+loaded via the \f(CW\*(C`USE\*(C'\fR directive and re-used for all subsequent
+\&\f(CW\*(C`FILTER\*(C'\fR operations. That means that any argument specified with
+the \f(CW\*(C`FILTER\*(C'\fR directive are ignored.
+.PP
+Dynamic filters, on the other hand, are re-created each time
+they are used by a \f(CW\*(C`FILTER\*(C'\fR directive. This allows them to act
+on any parameters passed from the \f(CW\*(C`FILTER\*(C'\fR directive and modify
+their behaviour accordingly.
+.PP
+There are two ways to create a dynamic filter. The first is to
+define a \f(CW$DYNAMIC\fR class variable set to a true value.
+.PP
+.Vb 3
+\& package MyOrg::Template::Plugin::MyFilter;
+\& use base 'Template::Plugin::Filter';
+\& our $DYNAMIC = 1;
+.Ve
+.PP
+The other way is to set the internal \f(CW\*(C`_DYNAMIC\*(C'\fR value within the \f(CW\*(C`init()\*(C'\fR
+method which gets called by the \f(CW\*(C`new()\*(C'\fR constructor.
+.PP
+.Vb 5
+\& sub init {
+\& my $self = shift;
+\& $self\->{ _DYNAMIC } = 1;
+\& return $self;
+\& }
+.Ve
+.PP
+When this is set to a true value, the plugin will automatically
+create a dynamic filter. The outcome is that the \f(CW\*(C`filter()\*(C'\fR method
+will now also get passed a reference to an array of postional
+arguments and a reference to a hash array of named parameters.
+.PP
+So, using a plugin filter like this:
+.PP
+.Vb 1
+\& [% FILTER $blat 'foo' 'bar' baz = 'blam' %]
+.Ve
+.PP
+would allow the \f(CW\*(C`filter()\*(C'\fR method to work like this:
+.PP
+.Vb 2
+\& sub filter {
+\& my ($self, $text, $args, $conf) = @_;
+.Ve
+.PP
+.Vb 3
+\& # $args = [ 'foo', 'bar' ]
+\& # $conf = { baz => 'blam' }
+\& }
+.Ve
+.PP
+In this case can pass parameters to both the \s-1USE\s0 and \s-1FILTER\s0 directives,
+so your \fIfilter()\fR method should probably take that into account.
+.PP
+.Vb 1
+\& [% USE MyFilter 'foo' wiz => 'waz' %]
+.Ve
+.PP
+.Vb 3
+\& [% FILTER $MyFilter 'bar' biz => 'baz' %]
+\& ...
+\& [% END %]
+.Ve
+.PP
+You can use the \f(CW\*(C`merge_args()\*(C'\fR and \f(CW\*(C`merge_config()\*(C'\fR methods to do a quick
+and easy job of merging the local (e.g. \f(CW\*(C`FILTER\*(C'\fR) parameters with the
+internal (e.g. \f(CW\*(C`USE\*(C'\fR) values and returning new sets of conglomerated
+data.
+.PP
+.Vb 2
+\& sub filter {
+\& my ($self, $text, $args, $conf) = @_;
+.Ve
+.PP
+.Vb 2
+\& $args = $self\->merge_args($args);
+\& $conf = $self\->merge_config($conf);
+.Ve
+.PP
+.Vb 4
+\& # $args = [ 'foo', 'bar' ]
+\& # $conf = { wiz => 'waz', biz => 'baz' }
+\& ...
+\& }
+.Ve
+.PP
+You can also have your plugin install itself as a named filter by
+calling the \f(CW\*(C`install_filter()\*(C'\fR method from the \f(CW\*(C`init()\*(C'\fR method. You
+should provide a name for the filter, something that you might
+like to make a configuration option.
+.PP
+.Vb 6
+\& sub init {
+\& my $self = shift;
+\& my $name = $self\->{ _CONFIG }\->{ name } || 'myfilter';
+\& $self\->install_filter($name);
+\& return $self;
+\& }
+.Ve
+.PP
+This allows the plugin filter to be used as follows:
+.PP
+.Vb 1
+\& [% USE MyFilter %]
+.Ve
+.PP
+.Vb 3
+\& [% FILTER myfilter %]
+\& ...
+\& [% END %]
+.Ve
+.PP
+or
+.PP
+.Vb 1
+\& [% USE MyFilter name = 'swipe' %]
+.Ve
+.PP
+.Vb 3
+\& [% FILTER swipe %]
+\& ...
+\& [% END %]
+.Ve
+.PP
+Alternately, you can allow a filter name to be specified as the
+first positional argument.
+.PP
+.Vb 6
+\& sub init {
+\& my $self = shift;
+\& my $name = $self\->{ _ARGS }\->[0] || 'myfilter';
+\& $self\->install_filter($name);
+\& return $self;
+\& }
+.Ve
+.PP
+.Vb 1
+\& [% USE MyFilter 'swipe' %]
+.Ve
+.PP
+.Vb 3
+\& [% FILTER swipe %]
+\& ...
+\& [% END %]
+.Ve
+.SH "EXAMPLE"
+.IX Header "EXAMPLE"
+Here's a complete example of a plugin filter module.
+.PP
+.Vb 3
+\& package My::Template::Plugin::Change;
+\& use Template::Plugin::Filter;
+\& use base qw( Template::Plugin::Filter );
+.Ve
+.PP
+.Vb 2
+\& sub init {
+\& my $self = shift;
+.Ve
+.PP
+.Vb 1
+\& $self\->{ _DYNAMIC } = 1;
+.Ve
+.PP
+.Vb 2
+\& # first arg can specify filter name
+\& $self\->install_filter($self\->{ _ARGS }\->[0] || 'change');
+.Ve
+.PP
+.Vb 2
+\& return $self;
+\& }
+.Ve
+.PP
+.Vb 2
+\& sub filter {
+\& my ($self, $text, $args, $config) = @_;
+.Ve
+.PP
+.Vb 2
+\& $config = $self\->merge_config($config);
+\& my $regex = join('|', keys %$config);
+.Ve
+.PP
+.Vb 1
+\& $text =~ s/($regex)/$config\->{ $1 }/ge;
+.Ve
+.PP
+.Vb 2
+\& return $text;
+\& }
+.Ve
+.PP
+.Vb 1
+\& 1;
+.Ve
+.SH "AUTHOR"
+.IX Header "AUTHOR"
+Andy Wardley <abw@wardley.org> <http://wardley.org/>
+.SH "COPYRIGHT"
+.IX Header "COPYRIGHT"
+Copyright (C) 1996\-2007 Andy Wardley. All Rights Reserved.
+.PP
+This module is free software; you can redistribute it and/or
+modify it under the same terms as Perl itself.
+.SH "SEE ALSO"
+.IX Header "SEE ALSO"
+Template::Plugin, Template::Filters, Template::Manual::Filters
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