If a role specifies a requires value, that value must be provided in the
consuming class.
It cannot be provided in a consuming role.
It cannot be provided in a separate role that is loaded earlier in the same
with statement.
It can only be provided in the parent class directly, or in a role consumed by
the parent class in an earlier with statement.
That means that you cannot provide a role that bundles up a bunch of roles to
make it easy to get the *right* collection loaded in the *right* order by all
end consumers. The separate with statement issue means that you lose the
cross-checking done by loading multiple roles in the same with statement.
Without looking into the internals of Roles, I suspect that the attributes of a
role are not installed into the consuming class until after the entire role has
been processed (which means that a with inside the role is processed too soon,
as well as being processing in the namespace of the consuming role rather than
the final consuming class).
Is there a good way to work around this?
$ for i in *; do echo ==== cat $i; cat $i; echo ====; echo ====
perl $i; perl $i; done
==== cat test1.pl
package BRole;
use Moose::Role;
requires 'b';
package ARole;
use Moose::Role;
has 'b' => ( is => 'ro', isa => 'Scalar' );
package main;
use Moose;
with 'ARole', 'BRole';
====
==== perl test1.pl
'ARole|BRole' requires the method 'b' to be implemented by 'main' at
/oicr/local/boutroslab/sw/NightlyBuilds/2014-11-21/perl/Perl-BL-2014-11-21/lib/site_perl/5.18.2/x86_64-linux/Moose/Exporter.pm
line 418
Moose::with('ARole', 'BRole') called at test1.pl line 13
==== cat test2.pl
package BRole;
use Moose::Role;
requires 'b';
package ARole;
use Moose::Role;
has 'b' => ( is => 'ro', isa => 'Scalar' );
with 'BRole';
package main;
use Moose;
with 'ARole';
====
==== perl test2.pl
'ARole' requires the method 'b' to be implemented by 'main' at
/oicr/local/boutroslab/sw/NightlyBuilds/2014-11-21/perl/Perl-BL-2014-11-21/lib/site_perl/5.18.2/x86_64-linux/Moose/Exporter.pm
line 418
Moose::with('ARole') called at test2.pl line 14
==== cat test3.pl
package BRole;
use Moose::Role;
requires 'b';
package ARole;
use Moose::Role;
has 'b' => ( is => 'ro', isa => 'Scalar' );
package main;
use Moose;
with 'ARole';
with 'BRole';
====
==== perl test3.pl
John Macdonald
Software Engineer
Ontario Institute for Cancer Research
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