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Id: 77406
Status: open
Priority: 0/
Queue: Moose

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Owner: Nobody in particular
Requestors: NMADDY1 [...] hfhs.org
Cc: CHOROBA [...] cpan.org
ribasushi [...] leporine.io
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Bug Information
Severity: (no value)
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Fixed in: (no value)

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Moose-theoretically_associated_method_names.diff



Subject: Attribute delegated in one role does not satisfy requires of another role
Date: Thu, 24 May 2012 13:03:06 -0400
To: "'bug-Moose [...] rt.cpan.org'" <bug-Moose [...] rt.cpan.org>
From: "Maddy, Noel" <NMADDY1 [...] hfhs.org>
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I have one role that provides a method by delegating it to an attribute, and another role that requires that method. When I try composing those two roles, Moose does not see the delegated method as satisfying the requires clause. I'm running Perl 5.14.2 under perlbrew on Fedora 16, with up-to-date CPAN, including Moose 2.0602. Here's a simplified example case, which gives the error: 'DelegatedYum|NeedsYum' requires the method 'yum' to be implemented by 'Composed' package HasYum; use Moose; has yum => ( is => 'ro', default => 37 ); package DelegatedYum; use Moose::Role; has has_yum => ( is => 'ro', default => sub { HasYum->new() }, handles => ['yum'] ); package NeedsYum; use Moose::Role; requires 'yum'; package Composed; use Moose; #with qw{ NeedsYum DelegatedYum }; with qw{ DelegatedYum NeedsYum }; Show quoted text
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The problem is that Moose::Meta::Role::Application:: {ToRole,RoleSummation} do not know what methods an attribute can provide. Moose::Meta::Attribute is capable of providing an accurate list of methods the attribute will provide (accessors, clearers, predicates, delegated methods, etc), but Moose::Meta::Role::Attribute is not. I've attached a patch which goes some way to solving this problem. It adds a method "_theoretically_associated_method_names" to Moose::Meta::Mixin::AttributeCore. This method returns a list of method names that will theoretically be provided by the attribute. It knows about all the Moose built-in stuff like clearers, predicates and built- ins, but third-party traits can obviously provide even more methods, and it won't know about them. The patch solves the reported issue, and gets seven of Moose's TODO tests passing. The patch doesn't modify the behaviour of Moose::Meta::Role::has_method. Perhaps it should?
Subject: Moose-theoretically_associated_method_names.diff

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It's been two years. Could someone knowledgeable please review the patch?
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On 2014-05-21 18:11:07, DAGOLDEN wrote: Show quoted text
> It's been two years. Could someone knowledgeable please review the patch?
BTW this is https://github.com/moose/Moose/pull/19 -- which does need a bit of updating for the changes to exceptions, but shouldn't need substantial revisions.
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On 2014-05-21 20:11:07, DAGOLDEN wrote: Show quoted text
> It's been two years. Could someone knowledgeable please review the patch?
Well, now it's been four years. I did review the PR. Basically, it's not the right approach, unfortunately.
Interestingly, if you change use Moose::Role to use Moo::Role in DelegatedYum, it starts to work.


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