#============================================================= -*-perl-*-
#
# Template::Manual::VMethods
#
# DESCRIPTION
#   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.
#
# AUTHOR
#   Andy Wardley  <abw@andywardley.com>
#
# COPYRIGHT
#   Copyright (C) 1996-2001 Andy Wardley.  All Rights Reserved.
#   Copyright (C) 1998-2001 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.
#
# REVISION
#   
#
#========================================================================


#------------------------------------------------------------------------
# IMPORTANT NOTE
#   This documentation is generated automatically from source
#   templates.  Any changes you make here may be lost.
# 
#   The 'docsrc' documentation source bundle is available for download
#   from http://www.template-toolkit.org/docs.html and contains all
#   the source templates, XML files, scripts, etc., from which the
#   documentation for the Template Toolkit is built.
#------------------------------------------------------------------------

=head1 NAME

Template::Manual::VMethods - Virtual Methods

=head1 DESCRIPTION

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.

=head2 Scalar Virtual Methods

=over 4 

=item defined

Returns true if the value is defined.

    [% user = get_user(uid) IF uid.defined %]

=item length

Returns the length of the string representation of the item:

    [% IF password.length < 8 %]
       Password too short, dumbass!
    [% END %]

=item repeat(n)

Repeat the string a specified number of times.

    [% name = 'foo' %]
    [% name.repeat(3) %]		# foofoofoo

=item 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

=item match(pattern)

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

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

=item search(pattern)

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.

=item split(pattern)

Calls Perl's split() function to split a string into a list of
strings.

    [% FOREACH dir = mypath.split(':') %]
       [% dir %]
    [% END %]

=item chunk(size)

Splits the value into a list of chunks of a certain size.

    [% ccard_no = "1234567824683579";
       ccard_no.chunk(4).join
    %]

Output:

    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;
       number.chunk(-3).join(',')
    %]

Output:

    1,234,567

=item list

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

=item hash 

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.

=item size

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

=back


=head2 Hash Virtual Methods

=over 4

=item 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 %]

=item 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 %]

=item import

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

=item 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' %]

=item size

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

=item item

Returns an item from the hash using a key passed as an argument.

    [% hash.item('foo') %]  # same as hash.foo

=item list

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 =E<gt> value pair
in the hash.

=back


=head2 List Virtual Methods

=over 4

=item 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 C<n>, they return the first or
last C<n> elements:

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

=item 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

=item reverse

Returns the items of the list in reverse order.

    [% FOREACH s = scores.reverse %]
       ...
    [% END %]

=item join

Joins the items in the list into a single string, using Perl's join 
function.

    [% items.join(', ') %]

=item grep

Returns a list of the items in the list that match a regular expression
pattern.

    [% FOREACH directory.files.grep('\.txt$') %]
       ...
    [% END %]

=item 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.

=item unshift(item), push(item)

Adds an item to the start/end of a list.

    [% mylist.unshift('prev item') %]
    [% mylist.push('next item')    %]

=item shift, pop

Removes the first/last item from the list and returns it.

    [% first = mylist.shift %]
    [% last  = mylist.pop   %]

=item unique

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 %]

=item merge

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.

=item 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) %]

=item 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 ]);
  %]

=back

=head2 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.

=head2 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 ];
    };

template:

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

=head1 AUTHOR

Andy Wardley E<lt>abw@andywardley.comE<gt>

L<http://www.andywardley.com/|http://www.andywardley.com/>




=head1 VERSION

Template Toolkit version 2.14, released on 04 October 2004.

=head1 COPYRIGHT

  Copyright (C) 1996-2004 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.



=cut

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