Template::Manual::VMethods - Virtual Methods


Template::Manual::VMethods - Virtual Methods


The Template Toolkit provides virtual methods for manipulating variable values. Most of them are analogous to regular Perl functions of the same names. This section describes the different virtual methods that can be applied to scalar, list and hash values.

Scalar Virtual Methods

Returns true if the value is defined.
    [% user = get_user(uid) IF uid.defined %]

Returns the length of the string representation of the item:
    [% IF password.length < 8 %]
       Password too short, dumbass!
    [% END %]

Repeat the string a specified number of times.
    [% name = 'foo' %]
    [% name.repeat(3) %]                # foofoofoo

replace(search, replace)
Outputs the string with all instances of the first argument (specified as a Perl regular expression) with the second.
    [% name = 'foo, bar & baz' %]
    [% name.replace('\W+', '_') %]    # foo_bar_baz

Performs a regular expression match on the string using the pattern passed as an argument. If the pattern matches the string then the method returns a reference to a list of any strings captured within parenthesis in the pattern.
    [% name = 'Larry Wall' %]
    [% matches = name.match('(\w+) (\w+)') %]
    [% matches.1 %], [% matches.0 %]            # Wall, Larry

If the pattern does not match then the method returns false, rather than returning an empty list which Perl and the Template Toolkit both consider to be a true value. This allows you to write expression like this.

    [% "We're not worthy!" IF name.match('Larry Wall') %]
    [% IF (matches = name.match('(\w+) (\w+)')) %]
       pattern matches: [% matches.join(', ') %]
    [% ELSE %]
       pattern does not match
    [% END %]

Any regex modifiers, like /s, should be added in the regex using the (?s) syntax. For example, to modify the regex to disregard whitespace (the /x switch), use:

    [% re = '(?x)
               [ ]
      matches = name.match(re);

Performs a similar function to 'match' but simply returns true if the string matches the regular expression pattern passed as an argument.
    [% name = 'foo bar baz' %]
    [% name.search('bar') ? 'bar' : 'no bar' %]     # bar

This virtual method is now deprecated in favour of 'match'. Move along now, there's nothing more to see here.

Calls Perl's split() function to split a string into a list of strings.
    [% FOREACH dir = mypath.split(':') %]
       [% dir %]
    [% END %]

Splits the value into a list of chunks of a certain size.
    [% ccard_no = "1234567824683579";


    1234 5678 2468 3579

If the size is specified as a negative number then the text will be chunked from right-to-left. This gives the correct grouping for numbers, for example.

    [% number = 1234567;



Return the value as a single element list. This can be useful if you have a variable which may contain a single item or a list and you want to treat them equally. The 'list' method can be called against a list reference and will simply return the original reference, effectively a no-op.
    [% thing.list.size %]  # thing can be a scalar or a list

Return the value as a hash reference containing a single entry with the key 'value' indicating the original scalar value. As with the 'list' virtual method, this is generally used to help massage data into different formats.

Always returns 1 for scalar values. This method is provided for consistency with the hash and list size methods.

Hash Virtual Methods

keys, values, each
The regular hash operators returning lists of keys, values or both. Note how we use a '$' prefix on the 'key' variable in this example to have it interpolated (i.e. replaced with its value) before use.
    [% FOREACH key = product.keys %]
       [% key %] => [% product.$key %]
    [% END %]

sort, nsort
Return a list of the keys, sorted alphabetically (sort) or numerically (nsort) according to the corresponding values in the hash.
    [% FOREACH n = phones.sort %]
       [% phones.$n %] is [% n %],
    [% END %]

The import method can be called on a hash array to import the contents of another hash array.
    [% hash1 = {
           foo => 'Foo',
           bar => 'Bar',
       hash2 = {
           wiz => 'Wiz',
           woz => 'Woz',
    [% hash1.import(hash2) %]
    [% hash1.wiz %]                     # Wiz

You can also call the import() method by itself to import a hash array into the current namespace hash.

    [% user = { id => 'lwall', name => 'Larry Wall' } %]
    [% import(user) %]
    [% id %]: [% name %]                # lwall: Larry Wall

defined, exists
Returns a true or false value if an item in the hash denoted by the key passed as an argument is defined or exists, respectively.
    [% hash.defined('somekey') ? 'yes' : 'no' %]
    [% hash.exists('somekey') ? 'yes' : 'no' %]

Returns the number of key => value pairs in the hash.

Returns an item from the hash using a key passed as an argument.
    [% hash.item('foo') %]  # same as hash.foo

Returns the contents of the hash in list form. An argument can be passed to indicate the desired items required in the list: 'keys' to return a list of the keys (same as hash.keys), 'values' to return a list of the values (same as hash.values), or 'each' to return as list of (key, value) pairs (same as hash.each). When called without an argument it returns a list of hash references, each of which contains a 'key' and 'value' item representing a single key => value pair in the hash.

List Virtual Methods

first, last
Returns the first/last item in the list. The item is not removed from the list.
    [% results.first %] to [% results.last %]

If either is given a numeric argument n, they return the first or last n elements:

    The first 5 results are [% results.first(5).join(", ") %].

size, max
Returns the size of a list (number of elements) and the maximum index number (size - 1), respectively.
    [% results.size %] search results matched your query

Returns the items of the list in reverse order.
    [% FOREACH s = scores.reverse %]
    [% END %]

Joins the items in the list into a single string, using Perl's join function.
    [% items.join(', ') %]

Returns a list of the items in the list that match a regular expression pattern.
    [% FOREACH directory.files.grep('\.txt$') %]
    [% END %]

sort, nsort
Returns the items in alpha (sort) or numerical (nsort) order.
    [% library = books.sort %]

An argument can be provided to specify a search key. Where an item in the list is a hash reference, the search key will be used to retrieve a value from the hash which will then be used as the comparison value. Where an item is an object which implements a method of that name, the method will be called to return a comparison value.

    [% library = books.sort('author') %]

In the example, the 'books' list can contains hash references with an 'author' key or objects with an 'author' method.

unshift(item), push(item)
Adds an item to the start/end of a list.
    [% mylist.unshift('prev item') %]
    [% mylist.push('next item')    %]

shift, pop
Removes the first/last item from the list and returns it.
    [% first = mylist.shift %]
    [% last  = mylist.pop   %]

Returns a list of the unique elements in a list, in the same order as in the list itself.
    [% mylist = [ 1, 2, 3, 2, 3, 4, 1, 4, 3, 4, 5 ] %]
    [% numbers = mylist.unique %]

While this can be explicitly sorted, it is not required that the list be sorted before the unique elements are pulled out (unlike the Unix command line utility).

    [% numbers = mylist.unique.sort %]

Returns a list composed of zero or more other lists:
    [% list_one = [ 1 2 3 ];
       list_two = [ 4 5 6 ];
       list_three = [ 7 8 9 ];
       list_four = list_one.merge(list_two, list_three);

The original lists are not modified.

slice(from, to)
Returns a slice of items in the list between the bounds passed as arguments. If the second argument, 'to', isn't specified, then it defaults to the last item in the list. The original list is not modified.
    [% first_three = list.slice(0,2) %]
    [% last_three  = list.slice(-3, -1) %]

splice(offset, length, list)
Behaves just like Perl's splice() function allowing you to selectively remove and/or replace elements in a list. It removes 'length' items from the list, starting at 'offset' and replaces them with the items in 'list'.
   [% play_game = [ 'play', 'scrabble' ];
      ping_pong = [ 'ping', 'pong' ];
      redundant = play_game.splice(1, 1, ping_pong);
      redundant.join;     # scrabble
      play_game.join;     # play ping pong

The method returns a list of the items removed by the splice. You can use the CALL directive to ignore the output if you're not planning to do anything with it.

    [% CALL play_game.splice(1, 1, ping_pong) %]

As well as providing a reference to a list of replacement values, you can pass in a list of items.

   [% CALL list.splice(-1, 0, 'foo', 'bar') %]

Be careful about passing just one item in as a replacement value. If it is a reference to a list then the contents of the list will be used. If it's not a list, then it will be treated as a single value. You can use square brackets around a single item if you need to be explicit:

  [% # push a single item, an_item
     CALL list.splice(-1, 0, an_item);
     # push the items from another_list
     CALL list.splice(-1, 0, another_list);
     # push a reference to another_list
     CALL list.splice(-1, 0, [ another_list ]);

Automagic Promotion of Scalar to List for Virtual Methods

In addition to the scalar virtual methods listed in the previous section, you can also call any list virtual method against a scalar. The item will be automagically promoted to a single element list and the appropriate list virtual method will be called.

One particular benefit of this comes when calling subroutines or object methods that return a list of items, rather than the preferred reference to a list of items. In this case, the Template Toolkit automatically folds the items returned into a list.

The upshot is that you can continue to use existing Perl modules or code that returns lists of items, without having to refactor it just to keep the Template Toolkit happy (by returning references to list). Class::DBI module is just one example of a particularly useful module which returns values this way.

If only a single item is returned from a subroutine then the Template Toolkit assumes it meant to return a single item (rather than a list of 1 item) and leaves it well alone, returning the single value as it is. If you're executing a database query, for example, you might get 1 item returned, or perhaps many items which are then folded into a list.

The FOREACH directive will happily accept either a list or a single item which it will treat as a list. So it's safe to write directives like this, where we assume that 'something' is bound to a subroutine which might return 1 or more items:

    [% FOREACH item = something %]
    [% END %]

The automagic promotion of scalars to single item lists means that you can also use list virtual methods safely, even if you only get one item returned. For example:

    [% something.first   %]
    [% something.join    %]
    [% something.reverse.join(', ') %]

Note that this is very much a last-ditch behaviour. If the single item return is an object with a 'first' method, for example, then that will be called, as expected, in preference to the list virtual method.

Defining Custom Virtual Methods

You can define your own virtual methods for scalars, lists and hash arrays. The Template::Stash package variables $SCALAR_OPS, $LIST_OPS and $HASH_OPS are references to hash arrays that define these virtual methods. HASH_OPS and LIST_OPS methods are subroutines that accept a hash/list reference as the first item. SCALAR_OPS are subroutines that accept a scalar value as the first item. Any other arguments specified when the method is called will be passed to the subroutine.

    # load Template::Stash to make method tables visible
    use Template::Stash;
    # define list method to return new list of odd numbers only
    $Template::Stash::LIST_OPS->{ odd } = sub {
        my $list = shift;
        return [ grep { $_ % 2 } @$list ];


    [% primes = [ 2, 3, 5, 7, 9 ] %]
    [% primes.odd.join(', ') %]         # 3, 5, 7, 9


Andy Wardley <abw@andywardley.com>



Template Toolkit version 2.10, released on 24 July 2003.


  Copyright (C) 1996-2003 Andy Wardley.  All Rights Reserved.
  Copyright (C) 1998-2002 Canon Research Centre Europe Ltd.

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

 Template::Manual::VMethods - Virtual Methods