From: Dave Rolsky <autarch@urth.org>
Date: Wed, 27 Aug 2008 17:56:27 +0000 (+0000)
Subject: document subclass problem with metaclass roles
X-Git-Tag: 0.55_04~2^2~10
X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=eaeacdd61bf62dacc95420413475bb1019141832;p=gitmo%2FMoose.git

document subclass problem with metaclass roles
---

diff --git a/lib/Moose/Util/MetaRole.pm b/lib/Moose/Util/MetaRole.pm
index f0b53c4..4724da7 100644
--- a/lib/Moose/Util/MetaRole.pm
+++ b/lib/Moose/Util/MetaRole.pm
@@ -203,6 +203,44 @@ once.
 
 This function will apply the specified roles to the object's base class.
 
+=head1 PROBLEMS WITH METACLASS ROLES AND SUBCLASS
+
+Because of the way this module works, there is an ordering problem
+which occurs in certain situations. This sequence of events causes an
+error:
+
+=over 4
+
+=item 1.
+
+There is a class (ClassA) which uses some extension(s) that apply
+roles to the metaclass.
+
+=item 2.
+
+You have another class (ClassB) which wants to subclass ClassA and
+apply some more extensions.
+
+=back
+
+Normally, the call to C<extends> will happen at run time, I<after> the
+additional extensions are applied. This causes an error when we try to
+make the metaclass for ClassB compatible with the metaclass for
+ClassA.
+
+We hope to be able to fix this in the future.
+
+For now the workaround is for ClassB to make sure it extends ClassA
+I<before> it loads extensions:
+
+  package ClassB;
+
+  use Moose;
+
+  BEGIN { extends 'ClassA' }
+
+  use MooseX::SomeExtension;
+
 =head1 AUTHOR
 
 Dave Rolsky E<lt>autarch@urth.orgE<gt>