The Perl Toolchain Summit needs more sponsors. If your company depends on Perl, please support this very important event.


Template::Plugin::VMethods - install vmethods


  package Template::Plugin::ReverseVMethod;
  use base qw(Template::Plugin::VMethods);
  @SCALAR_OPS = qw(reverse);

  sub reverse
     my $string = shift;
     scalar reverse $string;



Simple base class to allow your module to install and remove virtual methods into the Template Toolkit.

All you need to do in your package is declare one or more of the variables @LIST_OPS, @SCALAR_OPS or @HASH_OPS to indicate what virtual methods you want to export.

These can either be the names of functions in your package, or name/subroutine reference pairs.

For example, using named functions:

  package Template::Plugin::HexVMethod;
  use base qw(Template::Plugin::VMethods);
  @SCALAR_OPS = ( "hex" );
  sub hex { sprintf "%x", $_[0] };

For example, using the name and subroutine ref pairs:

  package Template::Plugin::DoubleVMethod;
  use base qw(Template::Plugin::VMethods);
  @SCALAR_OPS = ( double => \&double_string);
  @LIST_OPS   = ( double => \&double_list);
  sub double_string  { $_[0]x2             }
  sub double_list    { [ (@{ $_[0] }) x 2] }

For example, mixing the two freely:

  package CaesarVMethod;
  use base qw(Template::Plugin::VMethods);
  @SCALAR_OPS = ( "caesar",
                  "rot13"   => sub { caesar($_[0],"13") } );
  sub caesar
    $string = shift;
    $string =~ tr/A-Za-z/B-ZAb-za/ for 1..$_[0];
    return $string;

Using VMethods Based Plugins

Once you've done this people can use your plugin just like they would any other:

  [% USE CaesarVMethod %]
  [% foo = "Crbcyr jub yvxr gur pbybhe benatr ner fvyyl" %]
  The secret phrase is [% foo.rot13 %]

The vmethods will remain in effect till the end of the template, meaning all templates called from within this template (i.e. via PROCESS, INCLUDE, WRAPPER, etc) will be able to access the VMethods.

It's possible to permanently install the vmethods from perl space, so that all instances of Template everywhere will always have access to all the vmethods by using your plugin like so:

  use Template::Plugin::CaesarVMethod 'install';

Using subroutines from other classes.

Instead of writing virtual methods, you might be using the Template::Plugin::Procedural class:

  package Template::Plugin::MD5;
  use base qw(Template::Plugin::Procedural);
  use Digest::MD5;
  sub md5        { Digest::MD5::md5_hex(@_) };
  sub md5_base64 { Digest::MD5::md5_base64(@_) };

And you'll be calling the methods as so from within the template:

  [% USE MD5 %]
  [% MD5.md5(foo) %]

You'd rather use VMethods though, to do things like this:

  [% USE MD5VMethods %]
  [% foo.md5 %]

The obvious way to do this is to load the original class and take references to those subroutines:

  package Template::Plugin::MD5VMethods;
  use base qw(Template::Plugin::VMethods);
  use Template::Plugin::MD5;
  @SCALAR_OPS = (md5        => \&Template::Plugin::MD5::md5,
                 md5_base64 => \&Template::Plugin::MD5::md5_base64);

This can get awfully tedious very soon when you're attempting to re-wrap a class with many subroutines in it. Because of this Template::Plugin::VMethods allows you to use a special variable $VMETHOD_PACKAGE which can be used to alter the package this module uses to find named VMethods.

  package Template::Plugin::MD5VMethods;
  use base qw(Template::Plugin::VMethods);
  use Template::Plugin::MD5;
  $VMETHOD_PACKAGE = 'Template::Plugin::MD5';
  @SCALAR_OPS = qw(md5 md5_base64);


This module has an 'import' and a 'new' method; If you implement any of these in your subclass you'll need to chain the methods like this:

   sub new
      my $class = shift;
      my $this  = $class->SUPER::new(@_);


Even if you manually redefine a VMethod that this module has defined (by manually assigning to the $Template::Stash::*_OPS variables) then that VMethod will still be restored to the value that it had before the USE statement that installed the VMethod you are overriding as soon as you leave the template that that USE method was declared in.

Sharing $Template::Stash::*_OPS across threads will really screw this whole system up; But you weren't going to do that anyway, were you?

Further bugs (and requests for new features) can be reported to the author though the CPAN RT system:


Written by Mark Fowler <>

Copyright Mark Fowler 2003. All Rights Reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

Caesar code example adapted from Crypt::Caesar by Juerd