NAME
MooX::TaggedAttributes - Add a tag with an arbitrary value to a an attribute
VERSION
version 0.11
SYNOPSIS
# define a Tag Role
package T1;
use Moo::Role;
use MooX::TaggedAttributes -tags => [qw( t1 t2 )];
1;
# Apply a tag role directly to a class
package C1;
use Moo;
use T1;
has c1 => ( is => 'ro', t1 => 1 );
1;
# use a tag role in another Role
package R1;
use Moo::Role;
use T1;
has r1 => ( is => 'ro', t2 => 2 );
1;
# Use a tag role which consumes a tag role in a class
package C2;
use Moo;
use R1;
has c2 => ( is => 'ro', t2 => sub { } );
1;
# Use our tags
use C1;
use C2;
use 5.01001;
# get the value of the tag t1, applied to attribute a1
say C1->new->_tags->{t1}{a1};
# get the value of the tag t2, applied to attribute c2
say C2->new->_tags->{t2}{c2};
DESCRIPTION
This module attaches a tag-value pair to an attribute in a Moo class or role, and provides a interface to query which attributes have which tags, and what the values are.
Tagging Attributes
To define a set of tags, create a special tag role:
package T1;
use Moo::Role;
use MooX::TaggedAttributes -tags => [ 't1' ];
has a1 => ( is => 'ro', t1 => 'foo' );
1;
If there's only one tag, it can be passed directly without being wrapped in an array:
package T2;
use Moo::Role;
use MooX::TaggedAttributes -tags => 't2';
has a2 => ( is => 'ro', t2 => 'bar' );
1;
A tag role is a standard Moo::Role with added machinery to track attribute tags. As shown, attributes may be tagged in the tag role as well as in modules which consume it.
Tag roles may be consumed just as ordinary roles, but in order for role consumers to have the ability to assign tags to attributes, they need to be consumed with the Perl use statement, not with the with statement.
Consuming with the with statement will propagate attributes with existing tags, but won't provide the ability to tag new attributes.
This is correct:
package R2;
use Moo::Role;
use T1;
has r2 => ( is => 'ro', t1 => 'foo' );
1;
package R3;
use Moo::Role;
use R3;
has r3 => ( is => 'ro', t1 => 'foo' );
1;
The same goes for classes:
package C1;
use Moo;
use T1;
has c1 => ( is => 'ro', t1 => 'foo' );
1;
Combining tag roles is as simple as use'ing them in the new role:
package T12;
use Moo::Role;
use T1;
use T2;
1;
package C2;
use Moo;
use T12;
has c2 => ( is => 'ro', t1 => 'foo', t2 => 'bar' );
1;
Accessing tags
Classes and objects are provided a _tags method which returns a MooX::TaggedAttributes::Cache object. For backwards compatibility, it can be dereferenced as a hash, providing a hash of hashes keyed off of the tags and attribute names. For example, for the following code:
package T;
use Moo::Role;
use MooX::TaggedAttributes -tags => [qw( t1 t2 )];
1;
package C;
use Moo;
use T;
has a => ( is => 'ro', t1 => 2 );
has b => ( is => 'ro', t2 => 'foo' );
1;
The tag structure returned by C->_tags
{ t1 => { a => 2 }, t2 => { b => "foo" } }
and C->new->_tags
{ t1 => { a => 2 }, t2 => { b => "foo" } }
are identical.
BUGS AND LIMITATIONS
Changes to an object after instantiation are not tracked.
If a role with tagged attributes is applied to an object, the tags for those attributes are not visible.
SUPPORT
Bugs
Please report any bugs or feature requests to bug-moox-taggedattributes@rt.cpan.org or through the web interface at: https://rt.cpan.org/Public/Dist/Display.html?Name=MooX-TaggedAttributes
Source
Source is available at
https://gitlab.com/djerius/moox-taggedattributes
and may be cloned from
https://gitlab.com/djerius/moox-taggedattributes.git
AUTHOR
Diab Jerius djerius@cpan.org
COPYRIGHT AND LICENSE
This software is Copyright (c) 2018 by Smithsonian Astrophysical Observatory.
This is free software, licensed under:
The GNU General Public License, Version 3, June 2007
