A Wee Bit of Fun with Template::Declare

August 21st, 2011
PerlTemplate::DeclareDancerFile::SharedDir

A Wee Bit of Fun with Template::Declare

As I was crafting my Dancer presentation for Summercamp 2011, I noticed that there wasn’t a Dancer template for Template::Declare.

Well, now there’s one.

While I was at it, I also played with defining templates in their own files and then importing them in a Template::Declare class (for more involved templates, I like to have one template per file, to keep the strain on my brain to a minimum). With the magical help of Perl’s shared directories, it proved to be quite easy.

What I did was to use the auto directory associated with the template’s module. For example, for the template module My::Templates, I dropped the individual templates under the directory lib/auto/My/Templates:

    lib/
    ├── auto
    │   └── My
    │       └── Templates
    │           ├── simple.td
    │           └── sub
    │               └── foo.td
    └── My
        └── Templates.pm

Each template file only needs to have the inner template definition. For example, simple.td looks like:

    html {
        body {
            h1 { 'Hello ' . $args->{name} }
        }
    }

Because I’m piggy-backing on Perl’s shared directories convention, harvesting those template files is a breeze thanks to File::SharedDir.

    package My::Templates;

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

    use File::ShareDir qw/ module_dir /;
    use Path::Class;

    my $base =  dir( module_dir( __PACKAGE__ ) );

    $base->recurse( callback => &import_template );

    sub import_template {
        my $file = shift;

        return unless $file->isa( 'Path::Class::File' )
            and $file =~ /.td$/;

        my $content = $file->slurp;

        my $name = $file->relative( $base );

        $name =~ s/.td$//;

        eval <<"END_CODE";
    template "$name" => sub {
        my ( $self, $args ) = @_;

    #line 1 $f
        $content;
    }
    END_CODE

        die $@ if $@;
    }

    1;

As you can see, the code is pretty straight-forward and fairly minimal. With module_dir(), I grab all the files (recursively, natch) with a .td extension within the auto directory of the module and use them to build the equivalent ’template $name => sub { ... }’ declarations. The only bit of cleverness, if it can be called thus, is the ”#line 1 $f” preprocessing command, which will cause compilation errors to be reported at the right place in the .td template file instead than within My/Templates.pm.

In this example, I set the templates in such a way that the arguments must be passed as an hash ref and are made accessible to the template via $args, but it could easily be modified to please any other convention/preference.

And that’s all there is to it. The template module can be used like any other Template::Declare module, with no apparent difference for the outside world:

    #!/usr/bin/perl 

    use strict;
    use warnings;

    use My::Templates;

    Template::Declare->init( dispatch_to => [ 'My::Templates' ] );
    print Template::Declare->show( 'simple', { name => 'world' }  );
    print Template::Declare->show( 'sub/foo' );

Nice. Now, I should probably stop plucking the alpaca’s eyebrows and return to work on my slides…

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