Meta::Builder (3pm)

Meta programming is becoming more and more popular. The popularity of Meta programming comes from the fact that many problems are made significantly easier. There are a few specialized Meta tools out there, for instance <Class:MOP> which is used by Moose to track class metadata.

Meta::Builder is designed to be a generic tool for writing Meta objects. Unlike specialized tools, Meta::Builder makes no assumptions about what metrics you will care about. Meta::Builder also mkaes it simple for others to extend your meta-object based tools by providing hooks for other packages to add metrics to your meta object.

If a specialized Meta object tool is available to meet your needs please use it. However if you need a simple Meta object to track a couple metrics, use Meta::Builder.

Meta::Builder is also low-sugar and low-dep. In most cases you will not want a class that needs a meta object to use your meta-object class directly. Rather you will usually want to create a sugar class that exports enhanced \s-1API\s0 functions that manipulate the meta object.

My/Meta.pm:

    package My::Meta;
    use strict;
    use warnings;

    use Meta::Builder;

    # Name the accessor that will be defined in the class that uses the meta object
    # It is used to retrieve the classes meta object.
    accessor "mymeta";

    # Add a metric with two actions
    metric mymetric => sub { [] },
           pop => sub {
               my $self = shift;
               my ( $data ) = @_;
               pop @$data;
           },
           push => sub {
               my $self = shift;
               my ( $data, $metric, $action, @args ) = @_;
               push @$data => @args;
           };

    # Add an additional action to the metric
    action mymetric => ( get_ref => sub { shift });

    # Add some predefined metric types + actions
    hash_metric 'my_hashmetric';
    lists_metric 'my_listsmetric';

My.pm:

package My; use strict; use warnings;

use My::Meta;

My::Meta->new( _\|_PACKAGE_\|_ );

# My::Meta defines mymeta() as the accessor we use to get our meta object. # this is the ONLY way to get the meta object for this class.

mymeta()->mymetric_push( "some data" ); mymeta()->my_hashmetric_add( key => 'value' ); mymeta()->my_listsmetric_push( list => qw/valueA valueB/ );

# It works fine as an object/class method as well. _\|_PACKAGE_\|_->mymeta->do_thing(...);

...;

When you use Meta::Builder your class is automatically turned into a subclass of Meta::Builder::Base. In addition several \*(L"sugar\*(R" functions are exported into your namespace. To avoid the \*(L"sugar\*(R" functions you can simply sublass Meta::Builder::Base directly.

Wraper around \*(C`caller-\*(C'add_metric()>. See Meta::Builder::Base. Wraper around \*(C`caller-\*(C'add_action()>. See Meta::Builder::Base. Wraper around \*(C`caller-\*(C'add_hash_metric()>. See Meta::Builder::Base. Wraper around \*(C`caller-\*(C'add_lists_metric()>. See Meta::Builder::Base. Wraper around \*(C`caller-\*(C'hook_before()>. See Meta::Builder::Base. Wraper around \*(C`caller-\*(C'hook_after()>. See Meta::Builder::Base. Wraper around \*(C`caller-\*(C'set_accessor()>. See Meta::Builder::Base.

make_immutable()

Overrides all functions/methods that alter the meta objects meta-data. This in effect prevents anything from adding new metrics, actions, or hooks without directly editing the metadata.

Chad Granum [email protected]

Copyright (C) 2010 Chad Granum

Meta-Builder is free software; Standard perl licence.

Meta-Builder is distributed in the hope that it will be useful, but \s-1WITHOUT\s0 \s-1ANY\s0 \s-1WARRANTY\s0; without even the implied warranty of \s-1MERCHANTABILITY\s0 or \s-1FITNESS\s0 \s-1FOR\s0 A \s-1PARTICULAR\s0 \s-1PURPOSE\s0. See the license for more details.