with My::Config;

## some runtime information, eventually for the trait's method
has validDomain => (
    isa => 'Str',
    is => 'rw',
);

has alarmMailsTo => (
    traits => ['ConfigEmail'],
    conf_key => 'ALARM_MAILS_TO'
    parameter_callback => 'validDomain'  ## give a method name
    isa => 'ArrayRef[Str]',
    is => 'rw',
);
..

## Class role
role My::Config {
    method load() {
        ..
        ## $attr is a Moose::Meta::Attribute
        my $parameter_callback = $attr->parameter_callback;   
        $attr->parse($configString, $self->$parameter_callback());
        ..
    }
}

## Base Attribute Trait
role My::Config::AttrBase {
    has parameter_callback => (
        isa => 'Str',
        is => 'rw',
        required => 1,
    );
}

## Attribute Trait
role My::Config::ConfigEmail with My::Config::AttrBase {
    method parse($value!, @parameters) {
        # now this is a more generic API
    }
}