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<h1 class="headline">Template::Plugin::Filter</h1>
<h2 class="subhead">Base class for plugin filters</h1>
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<pre>package MyOrg::Template::Plugin::MyFilter;
use Template::Plugin::Filter;
use base qw( Template::Plugin::Filter );
sub filter {
my ($self, $text) = @_;
# ...mungify $text...
return $text;
}
# now load it...
<span class="tt">[% USE MyFilter %]</span>
# ...and use the returned object as a filter
<span class="tt">[% FILTER $MyFilter %]</span>
...
<span class="tt">[% END %]</span></pre>
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<p>
This module implements a base class for plugin filters. It hides the
underlying complexity involved in creating and using filters that get
defined and made available by loading a plugin.
</p>
<p>
To use the module, simply create your own plugin module that is inherited
from the <code>Template::Plugin::Filter</code> class.
</p>
<pre>package MyOrg::Template::Plugin::MyFilter;
use Template::Plugin::Filter;
use base qw( Template::Plugin::Filter );</pre>
<p>
Then simply define your <code>filter()</code> method. When called, you
get passed a reference to your plugin object (<code>$self</code>) and the
text to be filtered.
</p>
<pre>sub filter {
my ($self, $text) = @_;
# ...mungify $text...
return $text;
}</pre>
<p>
To use your custom plugin, you have to make sure that the Template
Toolkit knows about your plugin namespace.
</p>
<pre>my $tt2 = Template->new({
PLUGIN_BASE => 'MyOrg::Template::Plugin',
});</pre>
<p>
Or for individual plugins you can do it like this:
</p>
<pre>my $tt2 = Template->new({
PLUGINS => {
MyFilter => 'MyOrg::Template::Plugin::MyFilter',
},
});</pre>
<p>
Then you <code>USE</code> your plugin in the normal way.
</p>
<pre><span class="tt">[% USE MyFilter %]</span></pre>
<p>
The object returned is stored in the variable of the same name,
'<code>MyFilter</code>'. When you come to use it as a
<code>FILTER</code>, you should add a dollar prefix. This indicates that
you want to use the filter stored in the variable '<code>MyFilter</code>'
rather than the filter named '<code>MyFilter</code>', which is an
entirely different thing (see later for information on defining filters
by name).
</p>
<pre><span class="tt">[% FILTER $MyFilter %]</span>
...text to be filtered...
<span class="tt">[% END %]</span></pre>
<p>
You can, of course, assign it to a different variable.
</p>
<pre><span class="tt">[% USE blat = MyFilter %]</span>
<span class="tt">[% FILTER $blat %]</span>
...text to be filtered...
<span class="tt">[% END %]</span></pre>
<p>
Any configuration parameters passed to the plugin constructor from the
<code>USE</code> directive are stored internally in the object for
inspection by the <code>filter()</code> method (or indeed any other
method). Positional arguments are stored as a reference to a list in the
<code>_ARGS</code> item while named configuration parameters are stored
as a reference to a hash array in the <code>_CONFIG</code> item.
</p>
<p>
For example, loading a plugin as shown here:
</p>
<pre><span class="tt">[% USE blat = MyFilter 'foo' 'bar' baz = 'blam' %]</span></pre>
<p>
would allow the <code>filter()</code> method to do something like this:
</p>
<pre>sub filter {
my ($self, $text) = @_;
my $args = $self->{ _ARGS }; # [ 'foo', 'bar' ]
my $conf = $self->{ _CONFIG }; # { baz => 'blam' }
# ...munge $text...
return $text;
}</pre>
<p>
By default, plugins derived from this module will create static filters.
A static filter is created once when the plugin gets loaded via the
<code>USE</code> directive and re-used for all subsequent
<code>FILTER</code> operations. That means that any argument specified
with the <code>FILTER</code> directive are ignored.
</p>
<p>
Dynamic filters, on the other hand, are re-created each time they are
used by a <code>FILTER</code> directive. This allows them to act on any
parameters passed from the <code>FILTER</code> directive and modify their
behaviour accordingly.
</p>
<p>
There are two ways to create a dynamic filter. The first is to define a
<code>$DYNAMIC</code> class variable set to a true value.
</p>
<pre>package MyOrg::Template::Plugin::MyFilter;
use base 'Template::Plugin::Filter';
our $DYNAMIC = 1;</pre>
<p>
The other way is to set the internal <code>_DYNAMIC</code> value within
the <code>init()</code> method which gets called by the
<code>new()</code> constructor.
</p>
<pre>sub init {
my $self = shift;
$self->{ _DYNAMIC } = 1;
return $self;
}</pre>
<p>
When this is set to a true value, the plugin will automatically create a
dynamic filter. The outcome is that the <code>filter()</code> method will
now also get passed a reference to an array of postional arguments and a
reference to a hash array of named parameters.
</p>
<p>
So, using a plugin filter like this:
</p>
<pre><span class="tt">[% FILTER $blat 'foo' 'bar' baz = 'blam' %]</span></pre>
<p>
would allow the <code>filter()</code> method to work like this:
</p>
<pre>sub filter {
my ($self, $text, $args, $conf) = @_;
# $args = [ 'foo', 'bar' ]
# $conf = { baz => 'blam' }
}</pre>
<p>
In this case can pass parameters to both the USE and FILTER directives,
so your filter() method should probably take that into account.
</p>
<pre><span class="tt">[% USE MyFilter 'foo' wiz => 'waz' %]</span>
<span class="tt">[% FILTER $MyFilter 'bar' biz => 'baz' %]</span>
...
<span class="tt">[% END %]</span></pre>
<p>
You can use the <code>merge_args()</code> and <code>merge_config()</code>
methods to do a quick and easy job of merging the local (e.g.
<code>FILTER</code>) parameters with the internal (e.g. <code>USE</code>)
values and returning new sets of conglomerated data.
</p>
<pre>sub filter {
my ($self, $text, $args, $conf) = @_;
$args = $self->merge_args($args);
$conf = $self->merge_config($conf);
# $args = [ 'foo', 'bar' ]
# $conf = { wiz => 'waz', biz => 'baz' }
...
}</pre>
<p>
You can also have your plugin install itself as a named filter by calling
the <code>install_filter()</code> method from the <code>init()</code>
method. You should provide a name for the filter, something that you
might like to make a configuration option.
</p>
<pre>sub init {
my $self = shift;
my $name = $self->{ _CONFIG }->{ name } || 'myfilter';
$self->install_filter($name);
return $self;
}</pre>
<p>
This allows the plugin filter to be used as follows:
</p>
<pre><span class="tt">[% USE MyFilter %]</span>
<span class="tt">[% FILTER myfilter %]</span>
...
<span class="tt">[% END %]</span></pre>
<p>
or
</p>
<pre><span class="tt">[% USE MyFilter name = 'swipe' %]</span>
<span class="tt">[% FILTER swipe %]</span>
...
<span class="tt">[% END %]</span></pre>
<p>
Alternately, you can allow a filter name to be specified as the first
positional argument.
</p>
<pre>sub init {
my $self = shift;
my $name = $self->{ _ARGS }->[0] || 'myfilter';
$self->install_filter($name);
return $self;
}
<span class="tt">[% USE MyFilter 'swipe' %]</span>
<span class="tt">[% FILTER swipe %]</span>
...
<span class="tt">[% END %]</span></pre>
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<p>
Here's a complete example of a plugin filter module.
</p>
<pre>package My::Template::Plugin::Change;
use Template::Plugin::Filter;
use base qw( Template::Plugin::Filter );
sub init {
my $self = shift;
$self->{ _DYNAMIC } = 1;
# first arg can specify filter name
$self->install_filter($self->{ _ARGS }->[0] || 'change');
return $self;
}
sub filter {
my ($self, $text, $args, $config) = @_;
$config = $self->merge_config($config);
my $regex = join('|', keys %$config);
$text =~ s/($regex)/$config->{ $1 }/ge;
return $text;
}
1;</pre>
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<p>
Andy Wardley <abw@wardley.org> <a
href="http://wardley.org/">http://wardley.org/</a>
</p>
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<p>
Copyright (C) 1996-2007 Andy Wardley. All Rights Reserved.
</p>
<p>
This module is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
</p>
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</div>
<div class="body">
<p>
<a href="../../../modules/Template/Plugin.html">Template::Plugin</a>, <a
href="../../../modules/Template/Filters.html">Template::Filters</a>, <a
href="../../../manual/Filters.html">Template::Manual::Filters</a>
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<div id="palette">
<ul>
<li class="first"><a href="#" class="blue" onclick="set_style('Clear Blue')"></a></li>
<li><a href="#" class="orange" onclick="set_style('Clear Orange')"></a></li>
<li><a href="#" class="green" onclick="set_style('Clear Green')"></a></li>
<li><a href="#" class="purple" onclick="set_style('Clear Purple')"></a></li>
<li><a href="#" class="grey" onclick="set_style('Clear Grey')"></a></li>
</ul>
</div>
</div> </body>
</html>
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