Re: roles verify attribute contents when applied?

On Thu, 12 Jan 2012, Mark Hedges wrote:

> I don't know if I'm going about this in the right way.  I want to 
> represent a machine.  Machines may be different hardware types.  It gets 
> a role for the hardware type that supplies methods that might be able to 
> powercycle it.  I am applying the hardware-specific role using 
> apply_all_roles to the instance rather than consuming a role in the 
> class. (Since it gets a different role based on which type it is, and 
> each one of these roles supplies the same named method.) I just wanted 
> to double-check when I apply the role to the object that it is the 
> correct type.

It seems to me that this would be better written like this:

   package Machine;
   use Moose;

   has power_cycler => (
       is => 'ro',
       does => 'PowerCycler',
       handles => [ 'restart' ],
   );

In other words, make a separate object that represents the type of power 
cycler (or whatever you call it) and let that handle restarting the 
machine.

You may need to set up a circular reference between the two objects, in 
which case this may be necessary:

   sub BUILD {
       my $self = shift;

       $self->power_cycler->machine($self0;
   }

You should make one of these a weak ref (probably the ref from cycler to 
machine) to precent memory leaks.


-dave

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