Re: Role composition bug?

On Apr 8, 2012, at 6:25 PM, Poul Henning Sørensen wrote:

> 
> On 2012.04.08, at 21:31, Ovid wrote:
> 
>> Hi all,
>> 
>> I'm wondering if this is a known bug or a misunderstanding on my part (I assume the latter):
>> 
>>    use 5.10.0;
>>    { package Role::A; use Moose::Role; with 'Role::C'; }
>>    { package Role::B; use Moose::Role; with 'Role::C'; }
>>    { package Role::C; use Moose::Role; with 'Role::D'; }
>>    {
>>        package Role::D;
>>        use Moose::Role;
>> 
>>        sub foo {
>>            my $proto = shift;
>>            my $class = ref $proto // $proto;
>>            return "$class\::foo";
>>        }
>>    }
>>    package Consume;
>>    use Moose;
>>    with qw(Role::A Role::B);
>>    say Moose->VERSION;
>>    say Consume->foo;
>> 
>> That prints out:
>> 
>>    2.0402
>>    Can't locate object method "foo" via package "Consume" at roles.pl line 19.
>> 
>> Given that Role::C uses Role::D and the latter provides the 'foo()' method, that method should be provided to both Role::A and Role::B since they each consume Role::C. When consuming those roles, the Consume class should then have the 'foo()' method, but it does not.
>> 
>> Did I misunderstand something? (For the curious, my Role::Basic module has the same bug).
>> 
> 
> To me it seems you're having a "conflict" - foo() is available in both Role::A and Role::B, and you the consuming class Consume should resolve it by implementing the method foo() itself. It can use combinations of method exclusion and aliasing.

Actually, foo() shouldn't conflict since it is the same underlying CODE reference. I suspect that is actually where things are getting confused.

- Stevan

> 
> Now, in your (short) example, Role::D::foo acts the same way, but imaging foo() invoked something that was different in Role::A and Role::B, then Consume's foo() has to decide what is the wanted version of foo()...
> 
> Hope that this helps.
> 
> regards
> Poul Sørensen
> Basefarm AS