VMethods.pod
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#============================================================= -*-perl-*- # # Template::Manual::VMethods # # AUTHOR # Andy Wardley <abw@wardley.org> # # COPYRIGHT # Copyright (C) 1996-2022 Andy Wardley. All Rights Reserved. # # This module is free software; you can redistribute it and/or # modify it under the same terms as Perl itself. # #======================================================================== =head1 NAME Template::Manual::VMethods - Virtual Methods =head1 Scalar Virtual Methods =head2 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 =head2 collapse Returns the text with any leading and trailing whitespace removed and any internal sequences of whitespace converted to a single space [% text = " The bird\n is the word" %] [% text.collapse %] # The bird is the word =head2 defined Returns true if the value is defined. [% user = get_user(uid) IF uid.defined %] =head2 dquote Returns the text with any double quote characters escaped with a backslash prefix. Any newline characters in the text will be replaced with "\n". [% quote = 'He said "Oh really?"' %] [% quote.dquote %] # He said \"Oh really?\" =head2 hash Return the value as a hash reference containing a single entry with the key C<value> indicating the original scalar value. As with the C<list> virtual method, this is generally used to help massage data into different formats. =head2 lcfirst Returns the text with the first letter converted to lower case. [% word = 'BIRD' %] [% word.lcfirst %] # bIRD =head2 length Returns the length of the string representation of the item: [% IF password.length < 8 %] Password too short, dumbass! [% END %] =head2 empty Returns true if the string is empty: [% IF details.empty %] No details specified [% END %] =head2 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 C<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 =head2 lower Returns the text in lower case. [% word = 'BIRD' %] [% word.lower %] # bird =head2 match(pattern, global) 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); %] To perform a global search to match the pattern as many times as it appears in the source string, provide a true value for the C<global> argument following the pattern. [% text = 'bandanna'; text.match('an+', 1).join(', ') # an, ann %] =head2 repeat(n) Repeat the string a specified number of times. [% name = 'foo' %] [% name.repeat(3) %] # foofoofoo =head2 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 You can use C<$1>, C<$2>, etc., to reference captured parts (in parentheses) in the regular expression. Just be careful to I<single> quote the replacement string. If you use I<double> quotes then TT will try and interpolate the variables before passing the string to the C<replace> vmethod. [% name = 'FooBarBaz' %] [% name.replace('([A-Z])', ' $1') %] # Foo Bar Baz =head2 remove(pattern) Outputs the string with all instances of the pattern (specified as a Perl regular expression) removed. [% name = 'foo, bar & baz' %] [% name.remove('\W+') %] # foobarbaz =head2 search(pattern) Performs a similar function to L<match> but simply returns true if the string matches the regular expression pattern passed as an argument. [% name = 'foo bar baz' %] [% name.search('bar') ? 'bar' : 'no bar' %] # bar This virtual method is now deprecated in favour of L<match>. Move along now, there's nothing more to see here. =head2 size Always returns 1 for scalar values. This method is provided for consistency with the hash and list size methods. =head2 split(pattern) Calls Perl's C<split()> function to split a string into a list of strings. [% FOREACH dir IN mypath.split(':') %] [% dir %] [% END %] =head2 substr(offset, length, replacement) Returns a substring starting at C<offset>, for C<length> characters. [% str 'foo bar baz wiz waz woz') %] [% str.substr(4, 3) %] # bar If C<length> is not specified then it returns everything from the C<offset> to the end of the string. [% str.substr(12) %] # wiz waz woz If both C<length> and C<replacement> are specified, then the method replaces everything from C<offset> for C<length> characters with C<$replacement>. The substring removed from the string is then returned. [% str.substr(0, 11, 'FOO') %] # foo bar baz [% str %] # FOO wiz waz woz =head2 squote Returns the text with any single quote characters escaped with a backslash prefix. [% tim = "Tim O'Reilly" %] [% tim.squote %] # Tim O\'Reilly =head2 trim Returns the text with any leading and trailing whitespace removed. [% text = ' hello world ' %] [% text.trim %] # hello world =head2 ucfirst Returns the text with the first letter converted to upper case. [% word = 'bird' %] [% word.ucfirst %] # Bird =head2 upper Returns the text in upper case. [% word = 'bird' %] [% word.upper %] # BIRD =head1 Hash Virtual Methods =head2 keys Returns a list of keys in the hash. They are not returned in any particular order, but the order is the same as for the corresponding values method. [% FOREACH key IN hash.keys %] * [% key %] [% END %] If you want the keys in sorted order, use the list C<sort> method. [% FOREACH key IN hash.keys.sort %] * [% key %] [% END %] Having got the keys in sorted order, you can then use variable interpolation to fetch the value. This is shown in the following example by the use of C<$key> to fetch the item from C<hash> whose key is stored in the C<key> variable. [% FOREACH key IN hash.keys.sort %] * [% key %] = [% hash.$key %] [% END %] Alternately, you can use the C<pairs> method to get a list of key/value pairs in sorted order. =head2 values Returns a list of the values in the hash. As with the C<keys> method, they are not returned in any particular order, although it is the same order that the keys are returned in. [% hash.values.join(', ') %] =head2 items Returns a list of both the keys and the values expanded into a single list. [% hash = { a = 10 b = 20 }; hash.items.join(', ') # a, 10, b, 20 %] =head2 each This method currently returns the same thing as the C<items> method. However, please note that this method will change in the next major version of the Template Toolkit (v3) to return the same thing as the C<pairs> method. This will be done in an effort to make these virtual method more consistent with each other and how Perl works. In anticipation of this, we recommend that you stop using C<hash.each> and instead use C<hash.items>. =head2 pairs This method returns a list of key/value pairs. They are returned in sorted order according to the keys. [% FOREACH pair IN product.pairs %] * [% pair.key %] is [% pair.value %] [% END %] =head2 list Returns the contents of the hash in list form. An argument can be passed to indicate the desired items required in the list: C<keys> to return a list of the keys (same as C<hash.keys>), C<values> to return a list of the values (same as C<hash.values>), C<each> to return as list of key and values (same as C<hash.each>), or C<pairs> to return a list of key/value pairs (same as C<hash.pairs>). [% keys = hash.list('keys') %] [% values = hash.list('values') %] [% items = hash.list('each') %] [% pairs = hash.list('pairs') %] When called without an argument it currently returns the same thing as the C<pairs> method. However, please note that this method will change in the next major version of the Template Toolkit (v3) to return a reference to a list containing the single hash reference (as per the scalar list method). In anticipation of this, we recommend that you stop using C<hash.list> and instead use C<hash.pairs>. =head2 sort, nsort Return a list of the keys, sorted alphabetically (C<sort>) or numerically (C<nsort>) according to the corresponding values in the hash. [% FOREACH n IN phones.sort %] [% phones.$n %] is [% n %], [% END %] =head2 import The C<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 C<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 =head2 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' %] When called without any argument, C<hash.defined> returns true if the hash itself is defined (e.g. the same effect as C<scalar.defined>). =head2 delete Delete one or more items from the hash. [% hash.delete('foo', 'bar') %] =head2 size Returns the number of key/value pairs in the hash. =head2 empty Returns true if the hash is empty: [% IF config.empty %] No configuration available [% END %] =head2 item Returns an item from the hash using a key passed as an argument. [% hash.item('foo') %] # same as hash.foo =head1 List Virtual Methods =head2 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(", ") %]. =head2 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 =head2 empty Returns true if the list is empty: [% IF results.empty %] No results found [% END %] =head2 defined Returns a true or false value if the item in the list denoted by the argument is defined. [% list.defined(3) ? 'yes' : 'no' %] When called without any argument, C<list.defined> returns true if the list itself is defined (e.g. the same effect as C<scalar.defined>). =head2 reverse Returns the items of the list in reverse order. [% FOREACH s IN scores.reverse %] ... [% END %] =head2 join Joins the items in the list into a single string, using Perl's C<join()> function. [% items.join(', ') %] =head2 grep Returns a list of the items in the list that match a regular expression pattern. [% FOREACH directory.files.grep('\.txt$') %] ... [% END %] =head2 sort, nsort Returns the items in alpha (C<sort>) or numerical (C<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 C<books> list can contains hash references with an C<author> key or objects with an C<author> method. You can also specify multiple sort keys. [% library = books.sort('author', 'title') %] In this case the books will be sorted primarily by author. If two or more books have authors with the same name then they will be sorted by title. =head2 unshift(item), push(item) The C<push()> method adds an item or items to the end of list. [% mylist.push(foo) %] [% mylist.push(foo, bar) %] The C<unshift()> method adds an item or items to the start of a list. [% mylist.unshift(foo) %] [% mylist.push(foo, bar) %] =head2 shift, pop Removes the first/last item from the list and returns it. [% first = mylist.shift %] [% last = mylist.pop %] =head2 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 %] =head2 import Appends the contents of one or more other lists to the end of the current list. [% one = [ 1 2 3 ]; two = [ 4 5 6 ]; three = [ 7 8 9 ]; one.import(two, three); one.join(', '); # 1, 2, 3, 4, 5, 6, 7, 8, 9 %] Import also allows chaining. The below syntax is equivalent. [% one = [ 1 2 3 ]; two = [ 4 5 6 ]; three = [ 7 8 9 ]; one.import(two, three).join(', '); # 1, 2, 3, 4, 5, 6, 7, 8, 9 # or: one.import(two).import(three).join(', '); # 1, 2, 3, 4, 5, 6, 7, 8, 9 %] =head2 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. =head2 slice(from, to) Returns a slice of items in the list between the bounds passed as arguments. If the second argument, C<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) %] =head2 splice(offset, length, list) Behaves just like Perl's C<splice()> function allowing you to selectively remove and/or replace elements in a list. It removes C<length> items from the list, starting at C<offset> and replaces them with the items in C<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 C<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 ]); %] =head2 hash Returns a reference to a hash array comprised of the elements in the list. The even-numbered elements (0, 2, 4, etc) become the keys and the odd-numbered elements (1, 3, 5, etc) the values. [% list = ['pi', 3.14, 'e', 2.718] %] [% hash = list.hash %] [% hash.pi %] # 3.14 [% hash.e %] # 2.718 If a numerical argument is provided then the hash returned will have keys generated for each item starting at the number specified. [% list = ['beer', 'peanuts'] %] [% hash = list.hash(1) %] [% hash.1 %] # beer [% hash.2 %] # peanuts =head2 item Returns an item from the list using an index passed as an argument. [% list.item(0) %] # same as list.0 =head1 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). C<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 C<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 the C<something> variable is bound to a subroutine which may return one or more items: [% FOREACH item IN 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 C<first> method, for example, then that will be called, as expected, in preference to the list virtual method. =head1 Defining Custom Virtual Methods You can define your own virtual methods for scalars, lists and hash arrays. The L<Template::Stash> package variables C<$SCALAR_OPS>, C<$LIST_OPS> and C<$HASH_OPS> are references to hash arrays that define these virtual methods. C<HASH_OPS> and C<LIST_OPS> methods are subroutines that accept a hash/list reference as the first item. C<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 ]; }; Example template: [% primes = [ 2, 3, 5, 7, 9 ] %] [% primes.odd.join(', ') %] # 3, 5, 7, 9 TODO: document the define_vmethod() method which makes this even easier =cut # Local Variables: # mode: perl # perl-indent-level: 4 # indent-tabs-mode: nil # End: # # vim: expandtab shiftwidth=4:
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