alert.pl

#!/usr/bin/perl

use strict;
use warnings;

use Alert;

my $alert = Alert->new( 
                type => 'confirm'
            );
$alert->show();

Alert.pm

package Alert;

use Moose;

has 'type' => (
    is          => 'ro',
    isa         => 'Str',
    required    => 1,
);

has 'title' => (
    is          => 'ro',
    isa         => 'Str',
    lazy_build  => 1,
);

has 'content'   => (
    is          => 'rw',
    isa         => 'Maybe[Str]',
    lazy_build  => 1
);

sub _build_content {
    my ( $self ) = @_;
    return $self->content if $self->content;
    return $self->type eq 'alert'
           ? 'This is an alert'
           : 'Somthing else'
}

sub _build_title {
    my ( $self ) = @_;
    return $self->title if $self->title;
    return $self->type eq 'alert'
           ? 'alert'
           : 'Somthing else'
}

sub show {
    my ( $self ) = @_;
    print $self->title ." ". $self->content ."\n";
    return;
}

no Moose;
__PACKAGE__->meta->make_immutable();

1;