Hi everyone!
I need to make some page object, in which font options needs to be configured. So I made a Role called RolePage, in which has normal attribute textFont and textSize: 
package RolePage;
use Moose::Role;

has textFont => (
  is      => 'rw',
  isa     => 'Str',
  default => 'Courier'
);

has textSize => (
  is      => 'rw',
  isa     => 'Int',
  default => 12
);

[download]
In a concrete page class, It may need to contain special font objects for layout calculation: 
package CairoPage;

use Moose;
use Cairo;
with 'RolePage';

has cairoFont => (
  is  => 'bare',
  isa => 'Cairo::ScaledFont'
);

[download]
So, when changing on textFont or textSize occurred, such font object should be refreshed. It seems trigger mechanism is a optimum way to do that.
However:
- triggers must be subref in the same package of the attribute;
- triggers cannot be overrided by "+attrName" way;
- triggers cannot be arounded.
So how can I avoid those limitations?

In reply to Moose: possible way to implement trigger in other packages? by llancet

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