MooX::TaggedAttributes 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. It keeps track of tags for attributes through role composition as well as class inheritance. 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" bless({ t1 => { a => 2 }, t2 => { b => "foo" } }, "MooX::TaggedAttributes::Cache") and "C->new->_tags" bless({ t1 => { a => 2 }, t2 => { b => "foo" } }, "MooX::TaggedAttributes::Cache") are identical. INSTALLATION This is a Perl module distribution. It should be installed with whichever tool you use to manage your installation of Perl, e.g. any of cpanm . cpan . cpanp -i . Consult http://www.cpan.org/modules/INSTALL.html for further instruction. Should you wish to install this module manually, the procedure is perl Build.PL ./Build ./Build test ./Build install 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