On Fri, Jul 23, 2010 at 7:51 AM, Macdonald, John <
john-421.macdon...@morganstanley.com> wrote:
> Two items:
>
> 1. I was just surprised to discover that Moose::Role does not allow
> augmenting attributes.
>
> I was hoping to specify in the Role that an attribute was required, and
> most of the characteristics of the attribute. In the class that uses the
> role, it would augment the attribute to specify the actual value (with
> default). However, I get a complaint about a required attribute needing a
> default, handler, etc. when I do the "with Role", before I get a chance to
> augment the attribute with its value.
>
> I wanted the required to be specified in the role to ensure that any class
> that uses the role actually provided the default value (but didn't need to
> do anything else to describe the attribute).
>
> Is there an alternate approach for this?
>
>
> I think, you are looking for a builder - the more elegant approach to
defaults
In Role, specify the attribute and _require_ the builder method:
requires 'default_foo';
has foo => (is => 'rw', ..., builder => 'default_foo' );
now in the class, implement default_foo, and you are in business. If you
use the approach with 'requires' it'll even complain if the class didn't
implement it. Alternatively, if there is a true default, omit requires and
implement it in the Role to be overridden by classes.
> 2. Is there a way of allowing a ref as a default value? I'm setting up a
> class attribute - a 'ro' reference to a list of hashes, that the super-class
> will access (using the subclasses list to drive the actions specific to the
> subclass without requiring new code in each sub-class). I know I can use
> default => sub { \$table } but I was hoping that there was some sort of flag
> I could use to say that I really did want to have a common ref value shared
> by all objects of this class.
>
> How about
our $table = "Big Blob";
use constant table => \$table;
in the attribute define 'table' as a builder
You don't strictly speaking need use constant - a sub will do the same. I
just think, constants are pretty if it's what you mean.
- Kate
