Templa...Declare(3pm)

okay bestie, deep breath — this is Template::Declare(3pm) from the User Contributed Perl Documentation, and honestly? It's about to become your whole personality. 💖

🌸 NAME 🌸

Template::Declare — Perlish declarative templates.

---

✨ SYNOPSIS ✨

Here's the basic HTML situation, fr fr:

package MyApp::Templates;
use Template::Declare::Tags; # defaults to 'HTML'
use base 'Template::Declare';

template simple => sub {
    html {
        head {}
        body {
            p { 'Hello, world wide web!' }
        }
    }
};

package main;
use Template::Declare;
Template::Declare->init( dispatch_to => ['MyApp::Templates'] );
print Template::Declare->show( 'simple' );

and the output is giving:

 <html>
  <head></head>
  <body>
   <p>Hello, world wide web!
   </p>
  </body>
 </html>

---

🦋 DESCRIPTION 🦋

Template::Declare is a pure-Perl declarative HTML/XUL/RDF/XML templating system.

Yes. Another one. There are many others like it, but this one is ours.

A few key features and buzzwords:

• All templates are 100% pure Perl code
• Simple declarative syntax
• No angle brackets 🚫 < >
• "Native" XML namespace and declaration support
• Mixins
• Inheritance
• Delegation
• Public and private templates

---

🎀 GLOSSARY 🎀

template class

A subclass of Template::Declare in which one or more templates are defined using the template keyword, or that inherits templates from a super class.

template

Created with the template keyword, a template is a subroutine that uses tags to generate output.

attribute

An XML element attribute. For example, in <img src="foo.png" />, src is an attribute of the img element.

tag

A subroutine that generates XML element-style output. Tag subroutines execute blocks that generate the output, and can call other tags to generate a properly hierarchical structure.

tag set

A collection of related tags defined in a subclass of Template::Declare::TagSet for a particular purpose, and which can be imported into a template class. For example, Template::Declare::TagSet::HTML defines tags for emitting HTML elements.

wrapper

A subroutine that wraps the output from a template. Useful for wrapping template output in common headers and footers, for example.

dispatch class

A template class that has been passed to init() via the dispatch_to parameter. When show is called, only templates defined in or mixed into the dispatch classes will be executed.

path

The name specified for a template when it is created by the template keyword, or when a template is mixed into a template class.

mixin

A template mixed into a template class via mix. Mixed-in templates may be mixed in under prefix paths to distinguish them from the templates defined in the dispatch classes.

alias

A template aliased into a template class via alias. Aliased templates may be added under prefix paths to distinguish them from the templates defined in the dispatch classes.

package variable

Variables defined when mixing templates into a template class. These variables are available only to the mixed-in templates; they are not even accessible from the template class in which the templates were defined.

helper

A subroutine used in templates to assist in the generation of output, or in template classes to assist in the mixing-in of templates. Output helpers include outs() for rending text output and xml_decl() for rendering XML declarations. Mixin helpers include into for specifying a template class to mix into, and under for specifying a path prefix under which to mix templates.

---

💜 USAGE 💜

Like other Perl templating systems, there are two parts to Template::Declare: the templates, and the code that loads and executes the templates. Unlike other template systems, the templates are written in Perl classes. A simple HTML example lives up in the SYNOPSIS.

🌈 A slightly more advanced example

In this example, we'll show off how to set attributes on HTML tags, how to call other templates, and how to declare a private template that can't be called directly. We'll also show passing arguments to templates. First, the template class:

package MyApp::Templates;
use base 'Template::Declare';
use Template::Declare::Tags;

private template 'util/header' => sub {
    head {
        title { 'This is a webpage' };
        meta  {
            attr { generator => "This is not your father's frontpage" }
        }
    }
};

private template 'util/footer' => sub {
    my $self = shift;
    my $time = shift || gmtime;

    div {
        attr { id => "footer"};
        "Page last generated at $time."
    }
};

template simple => sub {
    my $self = shift;
    my $user = shift || 'world wide web';

    html {
        show('util/header');
        body {
            img { src is 'hello.jpg' }
            p {
                attr { class => 'greeting'};
                "Hello, $user!"
            };
        };
        show('util/footer', 'noon');
    }
};

A few notes on this example:

• Since no parameter was passed to use Template::Declare::Tags, the HTML tags are imported by default.
• The private keyword indicates that a template is private. That means that it can only be executed by other templates within the template class in which it's declared. By default, Template::Declare->show will not dispatch to it.
• The two private templates have longer paths than we've seen before: util/header and util/footer. They must of course be called by their full path names. You can put any characters you like into template names, but the use of Unix filesystem-style paths is the most common (following on the example of HTML::Mason).
• The first argument to a template is a class name. This can be useful for calling methods defined in the class.
• The show sub executes another template. In this example, the simple template calls show('util/header') and show('util/footer') in order to execute those private templates in the appropriate places.
• Additional arguments to show are passed on to the template being executed. Here, show('util/footer', 'noon') is passing noon to the util/footer template, with the result that the "last generated at" string will display noon instead of the default gmtime.
• In the same way, note that the simple template expects an additional argument, a user name.
• In addition to using attr to declare attributes for an element, you can use is, as in

img { src is 'hello.jpg' }

Now for executing the template:

package main;
use Template::Declare;
Template::Declare->init( dispatch_to => ['MyApp::Templates'] );
print Template::Declare->show( '/simple', 'TD user');

We've told Template::Declare to dispatch to templates defined in our template class. And notice how an additional argument gets passed to show(); that argument, TD user, will be passed to the simple template, where it'll be used in the $user variable.

The output looks like this:

 <html>
  <head>
   <title>This is a webpage</title>
   <meta generator="This is not your father&#39;s frontpage" />
  </head>
  <body>
   <img src="hello.jpg" />
   <p class="greeting">Hello, TD user!</p>
  </body>
  <div id="footer">Page last generated at Thu Sep  3 20:56:14 2009.</div>
 </html>

Note that the single quote in father's was quoted for you. We sanitize your output for you to help prevent cross-site scripting attacks. 🛡️

🦄 XUL

Template::Declare isn't limited to just HTML. Let's do XUL!

package MyApp::Templates;
use base 'Template::Declare';
use Template::Declare::Tags 'XUL';

template main => sub {
    xml_decl { 'xml', version => '1.0' };
    xml_decl {
        'xml-stylesheet',
        href => "chrome://global/skin/",
        type => "text/css"
    };
    groupbox {
        caption { attr { label => 'Colors' } }
        radiogroup {
            for my $id ( qw< orange violet yellow > ) {
                radio {
                    attr {
                        id    => $id,
                        label => ucfirst($id),
                        $id eq 'violet' ? (selected => 'true') : ()
                    }
                }
            } # for
        }
    }
};

The first thing to do in a template class is to subclass Template::Declare itself. This is required so that Template::Declare always knows that it's dealing with templates. The second thing is to use Template::Declare::Tags to import the set of tag subroutines you need to generate the output you want. In this case, we've imported tags to support the creation of XUL. Other tag sets include HTML (the default), and RDF.

Templates are created using the template keyword:

template main => sub { ... };

The first argument is the name of the template, also known as its path. In this case, the template's path is main (or /main, both are allowed (to keep both PHP and HTML::Mason fans happy). The second argument is an anonymous subroutine that uses the tag subs (and any other necessary code) to generate the output for the template.

The tag subs imported into your class take blocks as arguments, while a number of helper subs take other arguments. For example, the xml_decl helper takes as its first argument the name of the XML declaration to be output, and then a hash of the attributes of that declaration:

xml_decl { 'xml', version => '1.0' };

Tag subs are used by simply passing a block to them that generates the output. Said block may of course execute other tag subs in order to represent the hierarchy required in your output. Here, the radiogroup tag calls the radio tag for each of three different colors:

radiogroup {
    for my $id ( qw< orange violet yellow > ) {
        radio {
            attr {
                id    => $id,
                label => ucfirst($id),
                $id eq 'violet' ? (selected => 'true') : ()
            }
        }
    } # for
}

okay so quick sidebar about that attr sub, because it's lowkey doing a lot of work and nobody's giving it credit. That little helper is what adds attributes to the element created by whatever tag it's chillin' inside. So in that example we just looked at, id, label, and selected all get slapped onto each radio output. Cute, right? 🎀

Once your templates are written (slay), you obviously wanna run them. The way you do that: you tell Template::Declare which template classes to dispatch to, then you ask it to show you the output from a template. Like:

package main;
Template::Declare->init( dispatch_to => ['MyApp::Templates'] );
print Template::Declare->show( 'main' );

The path you hand to show can be either main or </main>, whatever your heart desires. Either way, the output is giving:

 <?xml version="1.0"?>
 <?xml-stylesheet href="chrome://global/skin/" type="text/css"?>

 <groupbox>
  <caption label="Colors" />
  <radiogroup>
   <radio id="orange" label="Orange" />
   <radio id="violet" label="Violet" selected="true" />
   <radio id="yellow" label="Yellow" />
  </radiogroup>
 </groupbox>

---

✨ Postprocessing ✨

Sometimes you just want simple syntax for inline elements, no cap. Here's how you use a postprocessor to emphasize text _like this_:

package MyApp::Templates;
use Template::Declare::Tags;
use base 'Template::Declare';

template before => sub {
    h1 {
        outs "Welcome to ";
        em { "my" };
        outs " site. It's ";
        em { "great" };
        outs "!";
    };
};

template after => sub {
    h1  { "Welcome to _my_ site. It's _great_!" };
    h2  { outs_raw "This is _not_ emphasized." };
    img { src is '/foo/_bar_baz.png' };
};

So we've defined two templates in our template class, with the paths before and after. The one new thing to clock here is the outs and outs_raw subs. outs XML-encodes its argument and outputs it. You can also just yeet a plain string inside a tag call and it'll output, but if you need to mix tags and plain text within a single tag call — like in the before template right up there — you're gonna need outs to get things to output the way you expect. outs_raw is the same vibe, except it does no XML encoding. None. Zero. 💀

Now let's peek at how we use these templates with a post-processor:

package main;
use Template::Declare;
Template::Declare->init(
    dispatch_to   => ['MyApp::Templates'],
    postprocessor => \&emphasize,
    strict        => 1,
);

print Template::Declare->show( 'before' );
print Template::Declare->show( 'after'  );

sub emphasize {
    my $text = shift;
    $text =~ s{_(.+?)_}{<em>$1</em>}g;
    return $text;
}

As per usual, we've told Template::Declare to dispatch to our template class. A new parameter to init() is postprocessor, which is a code reference that should expect the template output as an argument. Then it can transform that text however it sees fit before returning it for the final output. In this example, the emphasize subroutine goes hunting for text that's emphasized using _underscores_ and turns them into <em>emphasis</em> HTML elements. Iconic behavior. 👑

Then we execute both the before and the after templates, and the output ends up as:

 <h1>Welcome to
  <em>my</em> site. It&#39;s
  <em>great</em>!</h1>
 <h1>Welcome to <em>my</em> site. It&#39;s <em>great</em>!</h1>
 <h2>This is _not_ emphasized.</h2>
 <img src="/foo/_bar_baz.png" />

The thing to note here — and bestie, this is the whole point — is that text passed to outs_raw is not passed through the postprocessor, and neither are attribute values (like the img's src). So _bar_ stays _bar_. Periodt.

---

🦋 Inheritance 🦋

Templates are really just methods. That's it. That's the tea. So you can subclass your template packages to override some of those methods:

package MyApp::Templates::GenericItem;
use Template::Declare::Tags;
use base 'Template::Declare';

template 'list' => sub {
    my ($self, @items) = @_;
    div {
        show('item', $_) for @items;
    }
};
template 'item' => sub {
    my ($self, $item) = @_;
    span { $item }
};

package MyApp::Templates::BlogPost;
use Template::Declare::Tags;
use base 'MyApp::Templates::GenericItem';

template 'item' => sub {
    my ($self, $post) = @_;
    h1  { $post->title }
    div { $post->body }
};

So here we've got two template classes; the second one, MyApp::Templates::BlogPost, inherits from the first one, MyApp::Templates::GenericItem. And clock this: MyApp::Templates::BlogPost also overrides the item template. So let's execute these:

package main;
use Template::Declare;

Template::Declare->init( dispatch_to => ['MyApp::Templates::GenericItem'] );
print Template::Declare->show( 'list', 'foo', 'bar', 'baz' );

Template::Declare->init( dispatch_to => ['MyApp::Templates::BlogPost'] );
my $post = My::Post->new(title => 'Hello', body => 'first post');
print Template::Declare->show( 'item', $post );

First we execute the list template in the base class, passing in some items, and then we re-init() Template::Declare and execute its list template with an appropriate argument. Here's the output:

 <div>
  <span>foo</span>
  <span>bar</span>
  <span>baz</span>
 </div>

 <h1>Hello</h1>
 <div>first post</div>

So the override of the list template in the subclass works exactly as expected. For another example, see Jifty::View::Declare::CRUD.

---

🎀 Wrappers 🎀

There are two levels of wrappers in Template::Declare: template wrappers and smart tag wrappers. Let's get into it.

💅 Template Wrappers 💅

create_wrapper declares a wrapper subroutine that can be called like a tag sub, but can optionally take arguments that get passed to the wrapper sub. So say you wanted to wrap all the output of a template in the usual HTML headers and footers — very main character of you — you can do something like this:

package MyApp::Templates;
use Template::Declare::Tags;
use base 'Template::Declare';

BEGIN {
    create_wrapper wrap => sub {
        my $code = shift;
        my %params = @_;
        html {
            head { title { outs "Hello, $params{user}!"} };
            body {
                $code->();
                div { outs 'This is the end, my friend' };
            };
        }
    };
}

template inner => sub {
    wrap {
        h1 { outs "Hello, Jesse, s'up?" };
    } user => 'Jesse';
};

Note how the wrap wrapper function is available for calling after it's been declared in a BEGIN block. Also note how you can pass arguments to the function after the closing brace — and you don't need a comma there! Wild, I know. The vibes are immaculate.

The output from the inner template will look something like this:

 <html>
  <head>
   <title>Hello, Jesse!</title>
  </head>
  <body>
   <h1>Hello, Jesse, s&#39;up?</h1>
   <div>This is the end, my friend</div>
  </body>
 </html>

✨ Tag Wrappers ✨

Tag wrappers are similar to template wrappers, but mainly they function as syntax sugar for creating subroutines that behave just like tags but are allowed to contain arbitrary Perl code and to dispatch to other tags. To create one, you simply create a named subroutine with the prototype (&) so that its interface is the same as tags. Inside it, use smart_tag_wrapper to do the actual execution, like so:

package My::Template;
use Template::Declare::Tags;
use base 'Template::Declare';

sub myform (&) {
    my $code = shift;

    smart_tag_wrapper {
        my %params = @_; # set using 'with'
        form {
            attr { %{ $params{attr} } };
            $code->();
            input { attr { type => 'submit', value => $params{value} } };
        };
    };
}

template edit_prefs => sub {
    with(
        attr  => { id => 'edit_prefs', action => 'edit.html' },
        value => 'Save'
    ), myform {
        label { 'Time Zone' };
        input { type is 'text'; name is 'tz' };
    };
};

Note that in the edit_prefs template we've used with to set up the parameters that get passed to the smart wrapper. smart_tag_wrapper() is the device that lets you receive those parameters, and it also handles the magic of making sure the tags you execute within it are properly output. Here we've used myform similarly to form, only myform does something different with the with() arguments and outputs a submit element. Little overachiever. 🫶

Executing this template:

Template::Declare->init( dispatch_to => ['My::Template'] );
print Template::Declare->show('edit_prefs');

Yields this output:

 <form action="edit.html" id="edit_prefs">
  <label>Time Zone</label>
  <input type="text" name="tz" />
  <input type="submit" value="Save" />
 </form>

---

👑 Class Search Dispatching 👑

The classes you pass via the dispatch_to parameter to init() specify all of the templates that can be executed by subsequent calls to show(). Template::Declare searches through these classes in order to find those templates. So it can be genuinely useful, when you're building your template classes and figuring out which ones to use for a particular class to show(), to have templates that override other templates. This is basically the same energy as how an operating system searches all the paths in the $PATH environment variable looking for a program to run, and as HTML::Mason component roots or Template::Toolkit's INCLUDE_PATH parameter. iykyk. 🧚

For example, say you have this template class that defines a template you'll use for displaying images on your Web site:

package MyApp::UI::Standard;
use Template::Declare::Tags;
use base 'Template::Declare';

template image => sub {
    my ($self, $src, $title) = @_;
    img {
        src is $src;
        title is $title;
    };
};

As per usual, you can use it like so:

my @template_classes = 'MyApp::UI::Standard';
Template::Declare->init( dispatch_to => \@template_classes );
print Template::Declare->show('image', 'foo.png', 'Foo');

We're explicitly using a reference to @template_classes so that we can manage this list ourselves. Take the wheel, bestie.

The output of this will be:

 <div class="std">
  <img src="foo.png" title="Foo" />
  <p class="caption"></p>
 </div>

But say that in some sections of your site you need to have a more formal treatment of your photos. Maybe you publish photos from a wire service and need to provide an appropriate credit. You might write the template class like so:

package MyApp::UI::Formal;
use Template::Declare::Tags;
use base 'Template::Declare';

template image => sub {
    my ($self, $src, $title, $credit, $caption) = @_;
    div {
        class is 'formal';
        img {
            src is $src;
            title is $title;
        };
        p {
            class is 'credit';
            outs "Photo by $credit";
        };
        p {
            class is 'caption';
            outs $caption;
        };
    };
};

This, too, will work as expected, but the useful bit comes in when you're mixing and matching template classes to pass to dispatch_to before rendering a page. Maybe you always pass MyApp::UI::Standard to dispatch_to because it has all of your standard formatting templates. But when the code realizes that a particular page needs the more formal treatment, you can prepend the formal class to the list:

unshift @template_classes, 'MyApp::UI::Formal';
print Template::Declare->show(
    'image',
    'ap.png',
    'AP Photo',
    'Clark Kent',
    'Big news'
);
shift @template_classes;

In this way, the formal image template will be found first, yielding this output:

 <div class="formal">
  <img src="ap.png" title="AP Photo" />
  <p class="credit">Photo by Clark Kent</p>
  <p class="caption">Big news</p>
 </div>

At the end, we've shifted the formal template class off the dispatch_to list in order to restore the template classes to the default configuration, ready for the next request. iconic cleanup behaviour, honestly 💅

✨ Template Composition ✨

There are two methods of template composition: mixins and delegation. Their interfaces are very similar, the only difference being the template invocant. 👑

🎀 Mixins 🎀

Let's start with a mixin.

package MyApp::UtilTemplates;
use Template::Declare::Tags;
use base 'Template::Declare';

template content => sub {
    my $self  = shift;
    my @paras = @_;
    h1 { $self->get_title };
    div {
        id is 'content';
        p { $_ } for @paras;
    };
};

package MyApp::Templates;
use Template::Declare::Tags;
use base 'Template::Declare';
mix MyApp::UtilTemplates under '/util';

sub get_title { 'Kashmir' }

template story => sub {
    my $self = shift;
    html {
      head {
          title { "My Site: " . $self->get_title };
      };
      body {
          show( 'util/content' => 'first paragraph', 'second paragraph' );
      };
    };
};

The first template class, MyApp::UtilTemplates, defines a utility template, called content, for outputting the contents of page. Note its call to $self->get_title even though it doesn't have a get_title method. This is part of the mixin's "contract": it requires that the class it's mixed into have a get_title() method.

The second template class, MyApp::Templates, mixes MyApp::UtilTemplates into itself under the path /util and defines a get_title() method as required by the mixin. Then, its story template calls the mixed-in template as util/content, because the content template was mixed into the current template under /util. Get it? 😌

Now we can use the usual template invocation:

package main;
Template::Declare->init( dispatch_to => ['MyApp::Templates'] );
print Template::Declare->show('story');

To appreciate our output:

 <html>
  <head>
   <title>My Site: Kashmir</title>
  </head>
  <body>
   <h1>Kashmir</h1>
   <div id="content">
    <p>fist paragraph</p>
    <p>second paragraph</p>
   </div>
  </body>
 </html>

Mixins are a very useful tool for template authors to add reusable functionality to their template classes. But it's important to pay attention to the mixin contracts so that you're sure to implement the required API in your template class (here, the get_title() method). no cap bestie, don't skip the contract 💀

🦋 Aliases 🦋

Aliases are very similar to mixins, but implement delegation as a composition pattern, rather than mixins. The upshot is that there is no contract provided by an aliased class: it just works. This is because the invocant is the class from which the aliases are imported, and therefore it will dispatch to methods defined in the aliased class.

For example, say that you wanted to output a sidebar on pages that need one (perhaps your CMS has sidebar things). We can define a template class that has a template for that:

package MyApp::UI::Stuff;
use Template::Declare::Tags;
use base 'Template::Declare';

sub img_path { '/ui/css' }

template sidebar => sub {
    my ($self, $thing) = @_;
    div {
        class is 'sidebar';
        img { src is $self->img_path . '/sidebar.png' };
        p { $_->content } for $thing->get_things;
    };
};

Note the use of the img_path() method defined in the template class and used by the sidebar template. Now let's use it:

package MyApp::Render;
use Template::Declare::Tags;
use base 'Template::Declare';
alias MyApp::UI::Stuff under '/stuff';

template page => sub {
    my ($self, $page) = @_;
    h1 { $page->title };
    for my $thing ($page->get_things) {
        if ($thing->is('paragraph')) {
            p { $thing->content };
        } elsif ($thing->is('sidebar')) {
            show( '/stuff/sidebar' => $thing );
        }
    }
};

Here our rendering template class has aliased MyApp::UI::Stuff under /stuff. So the page template calls show('/stuff/sidebar') to invoke the sidebar template. If we run this:

Template::Declare->init( dispatch_to => ['MyApp::Render'] );
print Template::Declare->show( page => $page );

We get output as you might expect:

 <h1>My page title</h1>
 <p>Page paragraph</p>
 <div class="sidebar">
  <img src="/ui/css/sidebar.png" />
  <p>Sidebar paragraph</p>
  <p>Another paragraph</p>
 </div>

Now, let's say that you have political stuff that you want to use a different image for in the sidebar. If that's the only difference, we can subclass MyApp::UI::Stuff and just override the img_path() method:

package MyApp::UI::Stuff::Politics;
use Template::Declare::Tags;
use base 'MyApp::UI::Stuff';

sub img_path { '/politics/ui/css' }

Now let's mix that into a politics template class:

package MyApp::Render::Politics;
use Template::Declare::Tags;
use base 'Template::Declare';
alias MyApp::UI::Stuff::Politics under '/politics';

template page => sub {
    my ($self, $page) = @_;
    h1 { $page->title };
    for my $thing ($page->get_things) {
        if ($thing->is('paragraph')) {
            p { $thing->content };
        } elsif ($thing->is('sidebar')) {
            show( '/politics/sidebar' => $thing );
        }
    }
};

The only difference between this template class and MyApp::Render is that it aliases MyApp::UI::Stuff::Politics under /politics, and then calls show('/politics/sidebar') in the page template. Running this template:

Template::Declare->init( dispatch_to => ['MyApp::Render::Politics'] );
print Template::Declare->show( page => $page );

Yields output using the value of the subclass's img_path() method -- that is, the sidebar image is now /politics/ui/css/sidebar.png instead of /ui/css/sidebar.png:

 <h1>My page title</h1>
 <p>Page paragraph</p>
 <div class="sidebar">
  <img src="/politics/ui/css/sidebar.png" />
  <p>Sidebar paragraph</p>
  <p>Another paragraph</p>
 </div>

🌈 Other Tricks 🌈

The delegation behavior of alias actually makes it a decent choice for template authors to mix and match libraries of template classes as appropriate, without worrying about side effects. You can even alias templates in one template class into another template class if you're not the author of that class by using the into keyword:

alias My::UI::Widgets into Your::UI::View under '/widgets';

Now the templates defined in Your::UI::View are available in My::UI::Widgets under /widgets. The mix method supports this syntax as well, though it's not necessarily recommended, given that you would not be able to fulfill any contracts unless you re-opened the class into which you mixed the templates. But in any case, authors of framework view classes might find this functionality useful for automatically aliasing template classes into a single dispatch template class.

Another trick is to alias or mix your templates with package variables specific to the composition. Do so via the setting keyword:

package My::Templates;
mix Some::Mixin under '/mymix', setting { name => 'Larry' };

The templates mixed from Some::Mixin into My::Templates have package variables set for them that are accessible only from their mixed-in paths. For example, if you define this template in Some::Mixin:

template howdy => sub {
    my $self = shift;
    outs "Howdy, " . $self->package_variable('name') || 'Jesse';
};

Then show('mymix/howdy') called on My::Templates will output "Howdy, Larry", while the output from show('howdy') will output "Howdy, Jesse". In other words, package variables defined for the mixed-in templates are available only to the mixins and not to the original. The same functionality exists for alias as well. iykyk 💅

✨ Indentation configuration ✨

By default, Template::Declare renders a readable XML adding end of lines and a one column indentation. This behavior could break a webpage design or add a significant amount of chars to your XML output. This could be changed by overwriting the default values. So,

$Template::Declare::Tags::TAG_INDENTATION  = 0;
$Template::Declare::Tags::EOL              = "";
say Template::Declare->show('main');

will render

<html><body><p>hi</p></body></html>

squished and proud of it 🫶

🛠 METHODS 🛠

---

init 💖

This is a class method and it initializes the whole Template::Declare system. Basically the "wake up bestie, we're rendering" button. ✨

dispatch_to

An array reference of classes to search for templates. Template::Declare will search this list of classes in order to find a template path. Order matters, ok? 👑

roots

Deprecated. It's just like dispatch_to, except the classes are searched in reverse order. It's kept around for backward compatibility, and for the pleasure of those who want to keep using Template::Declare the way that Jesse's "crack-addled brain" intended. 😭 No notes, iconic behavior, we love a legacy.

postprocessor

A coderef that gets called to postprocess the HTML or XML output of your templates. The whole point is to alleviate using Tags for simple text markup. 🎀

around_template

A coderef that's called instead of rendering each template. It receives four arguments: a coderef to invoke to render the template, the template's path, an arrayref of the arguments to the template, and the coderef of the template itself. Use it for instrumentation, bestie. For example:

Template::Declare->init(around_template => sub {
    my ($orig, $path, $args, $code) = @_;
    my $start = time;
    $orig->();
    warn "Rendering $path took " . (time - $start) . " seconds.";
});

Look at her timing her own templates. Main character energy, fr fr. ⏱️

strict

Die in exceptional situations — like when a template can't be found — instead of just warning. It's false by default, for backward compatibility. That default may change in the future, so specifying the value explicitly is recommended. Don't be the girl who leaves it undefined and gets jumpscared later. 💀

---

show TEMPLATE_NAME 🌸

Template::Declare->show( 'howdy', name => 'Larry' );
my $output = Template::Declare->show('index');

Call show with a template_name and Template::Declare will render that template. Any subsequent arguments get passed along to the template. Content generated by show() can be accessed via the output() method — but only if the output method you've chosen returns content instead of outputting it directly. iykyk. 💅

If it's called in scalar context, this method will also just return the content when it's available. Slay.

---

Template Composition 🦋

Sometimes you want to mix templates from one class into another class, or delegate template execution to a class of templates. alias() and mix() are your keys to doing so, bestie. 🔑

mix

mix Some::Clever::Mixin      under '/mixin';
mix Some::Other::Mixin       under '/otmix', setting { name => 'Larry' };
mix My::Mixin into My::View, under '/mymix';

Mixes templates from one template class into another class. When the mixed-in template is called, its invocant will be the class into which it was mixed. This type of composition is known as a "mixin" in object-oriented parlance. See Template Composition for extended examples and a comparison to alias. 📚

The first parameter is the name of the template class to be mixed in. The under keyword tells mix where to put the templates. So like, a foo template in Some::Clever::Mixin will be mixed in as mixin/foo. ✨

The setting keyword specifies package variables available only to the mixed-in copies of templates. Those are available to the templates as $self->package_variable($varname). 🫶

The into keyword tells mix into what class to mix the templates. Without this keyword, mix will mix them into the calling class. Periodt.

For those who prefer a direct OO syntax for mixins, just call mix() as a method on the class to be mixed in. To replicate the above three examples without the use of the sugar:

Some::Clever::Mixin->mix( '/mixin' );
Some::Other::Mixin->mix( '/otmix', { name => 'Larry' } );
My::Mixin->mix( 'My::View', '/mymix' );

alias

alias Some::Clever:Templates   under '/delegate';
alias Some::Other::Templates   under '/send_to', { name => 'Larry' };
alias UI::Stuff into My::View, under '/mystuff';

Aliases templates from one template class into another class. When an alias is called, its invocant will be the class from which it was aliased. This type of composition is known as "delegation" in object-oriented parlance. See Template Composition for extended examples and a comparison to mix. 🎀

The first parameter is the name of the template class to alias. The under keyword tells alias where to put the templates. For example, a foo template in Some::Clever::Templates will be aliased as delegate/foo. 🌈

The setting keyword specifies package variables available only to the aliases. These are available to the templates as $self->package_variable($varname). 💜

The into keyword tells alias into what class to alias the templates. Without this keyword, alias will alias them into the calling class.

For those who prefer a direct OO syntax for mixins, just call alias() as a method on the class to be mixed in. To replicate the above three examples without the use of the sugar:

Some::Clever:Templates->alias( '/delegate' );
Some::Other::Templates->alias( '/send_to', { name => 'Larry' } );
UI::Stuff->alias( 'My::View', '/mystuff' );

package_variable( VARIABLE )

$td->package_variable( $varname => $value );
$value = $td->package_variable( $varname );

Returns a value set for a mixed-in template's variable, if any were specified when the template was mixed-in. See mix for details. 🍓

package_variables( VARIABLE )

$td->package_variables( $variables );
$variables = $td->package_variables;

Get or set a hash reference of variables for a mixed-in template. See mix for details. 💅

---

Templates registration and lookup 🔍

resolve_template TEMPLATE_PATH INCLUDE_PRIVATE_TEMPLATES

my $code = Template::Declare->resolve_template($template);
my $code = Template::Declare->has_template($template, 1);

Turns a template path (TEMPLATE_PATH) into a CODEREF. If the boolean INCLUDE_PRIVATE_TEMPLATES is true, it resolves private templates in addition to public ones. has_template() is an alias for this method. 🪄

First it looks through all the valid Template::Declare classes defined via dispatch_to. For each class, it looks to see if it has a template called $template_name directly (or via a mixin).

has_template TEMPLATE_PATH INCLUDE_PRIVATE_TEMPLATES

An alias for resolve_template. That's it, that's the whole thing. ✨

register_template( TEMPLATE_NAME, CODEREF )

MyApp::Templates->register_template( howdy => sub { ... } );

This method registers a template called TEMPLATE_NAME in the calling class. As you might guess, CODEREF defines the template's implementation. This method is mainly intended to be used internally, because you use the template keyword to create templates, right? 😌

register_private_template( TEMPLATE_NAME, CODEREF )

MyApp::Templates->register_private_template( howdy => sub { ... } );

This method registers a private template called TEMPLATE_NAME in the calling class. As you might guess, CODEREF defines the template's implementation. 🎀

Private templates can't be called directly from user code — only from other templates. So like, besties only. 💖

This method is mainly intended to be used internally, as you use the private template expression to create templates, right? 🙈

buffer

Gets or sets the String::BufferStack object; this is a class method. 🧚

You can use it to manipulate the output from tags as they are output. It's used internally to make the tags nest correctly, and be output to the right place. We're not sure if there's ever a need for you to frob it by hand, but it does enable things like the following:

template simple => sub {
   html {
       head {}
       body {
           Template::Declare->buffer->set_filter( sub {uc shift} );
           p { 'Whee!' }
           p { 'Hello, world wide web!' }
           Template::Declare->buffer->clear_top if rand() < 0.5;
       }
   }
};

...which outputs, with equal regularity, either:

<html>
 <head></head>
 <body>
  <P>WHEE!</P>
  <P>HELLO, WORLD WIDE WEB!</P>
 </body>
</html>

...or:

<html>
 <head></head>
 <body></body>
</html>

We'll leave it to you to judge whether or not that's actually useful. 😭 Not me gambling my entire HTML body on rand(). 💀

---

Helpers 🫶

You don't need to call any of this directly. Genuinely. Hands off, bestie. 🙈

into

$class = into $class;

into is a helper method providing semantic sugar for the mix method. All it does is return the name of the class on which it was called. That's the entire job. Iconic minimalism. ⭐

---

Old, deprecated or just better to avoid 💀

import_templates

import_templates MyApp::Templates under '/something';

Like mix(), but without support for the into or setting keywords. Meaning: it mixes templates into the calling template class and does not support package variables for those mixins.

Deprecated in favor of mix. It will be supported for a long time, but new code should use mix(). 👑

new_buffer_frame

$td->new_buffer_frame;
# same as
$td->buffer->push( private => 1 );

Creates a new buffer frame, using push in String::BufferStack with private.

Deprecated in favor of dealing with buffer directly.

end_buffer_frame

my $buf = $td->end_buffer_frame;
# same as
my $buf = $td->buffer->pop;

Deletes and returns the topmost buffer, using pop in String::BufferStack.

Deprecated in favor of dealing with buffer directly.

path_for $template

my $path = Template::Declare->path_for('index');

Returns the path for the template name to be used for show, adjusted with paths used in mix. Note that this will only work for the last class into which you imported the template. This method is, therefore, deprecated. 🚫

Like, she only remembers the last one. That's the whole problem. 😭

💀 PITFALLS 💀

ok so here's the thing bestie — we're literally reusing the whole perl interpreter as the engine for our templating language, and Perl was not designed for this specific lil job. so there's some traps. here are the known ones to watch out for while you're scripting your templates with this module. 🫶

• it's super common to see tag sub calling statements chillin' without trailing semi-colons right after }. like this:

template foo => sub {
    p {
        a { attr { src => '1.png' } }
        a { attr { src => '2.png' } }
        a { attr { src => '3.png' } }
    }
};

is equivalent to:

template foo => sub {
    p {
        a { attr { src => '1.png' } };
        a { attr { src => '2.png' } };
        a { attr { src => '3.png' } };
    };
};

BUT xml_decl is a notable exception, and she is not like the other girls. always, always put a trailing semicolon after xml_decl { ... }, or you will mess up the order of output. no cap. 💅

• another place that requires a trailing semicolon is the statements before a Perl looping statement, an if statement, or a show call. for example:

p { "My links:" };
for (@links) {
    with ( src => $_ ), a {}
}

the ; after p { ... } is required here, or Perl will complain about syntax errors. it's giving drama. 😭

another example is:

h1 { 'heading' };  # this trailing semicolon is mandatory
show 'tag_tag'

• the is syntax for declaring tag attributes also requires a trailing semicolon, unless it is the only statement in a block. for example:

p { class is 'item'; id is 'item1'; outs "This is an item" }
img { src is 'cat.gif' }

• literal strings that have tag siblings won't be captured. so the following template:

p { 'hello'; em { 'world' } }

produces:

<p>
 <em>world</em>
</p>

instead of the desired output:

<p>
 hello
 <em>world</em>
</p>

you can use outs here to solve this problem:

p { outs 'hello'; em { 'world' } }

note you can always get rid of outs if the string literal is the only element of the containing block:

p { 'hello, world!' }

• look out!! if the if block is the last block/statement and the condition part is evaluated to be 0:

p { if ( 0 ) { } }

produces:

<p>0</p>

instead of the more intuitive output:

<p></p>

this is because if ( 0 ) is the last expression, so 0 is returned as the value of the whole block, which is then used as the content of the <p> tag. sneaky!! 🙈

to get rid of this, just put an empty string at the end so it returns empty string as the content instead of 0:

p { if ( 0 ) { } '' }

---

🐛 BUGS 🐛

Crawling all over, baby. Be very, very careful. This code is so cutting edge, it can only be fashioned from carbon nanotubes. But we're already using this thing in production :) Make sure you have read the PITFALLS section above :) 💖

Some specific bugs and design flaws that we'd love to see fixed.

Output isn't streamy.

If you run into bugs or misfeatures, please report them to bug-template-declare@rt.cpan.org. 📨

---

👀 SEE ALSO 👀

• Template::Declare::Tags
• Template::Declare::TagSet
• Template::Declare::TagSet::HTML
• Template::Declare::TagSet::XUL
• Jifty

---

✨ AUTHOR ✨

Jesse Vincent <jesse@bestpractical.com>

---

📜 LICENSE 📜

Template::Declare is Copyright 2006-2010 Best Practical Solutions, LLC.

Template::Declare is distributed under the same terms as Perl itself.

---

and that's a wrap on the whole page, bestie 🎀 this one shipped with perl v5.34.0 and the date on it is 2022-06-17, from the Templa...Declare(3pm) source — go forth and template responsibly, mwah 💅✨