Example Builder Pattern in Moose ("http://en.wikipedia.org/wiki/Builder_pattern")

builder_example.t

use Test::Most;

{
  package Pizza;

  use Moose;

  has [qw/dough sauce topping/] => (is=>'rw');

  package PizzaBuilder;

  use Moose::Role;

  requires qw/build_dough build_sauce build_topping/;

  has pizza => (is=>'ro', isa=>'Pizza',
    builder=>'_build_pizza', required=>1);

  sub _build_pizza { Pizza->new }

  package HawaiianPizzaBuilder;

  use Moose;
  with 'PizzaBuilder';

  sub build_dough { shift->pizza->dough('cross') }
  sub build_sauce { shift->pizza->sauce('mild') }
  sub build_topping { shift->pizza->topping('ham+pineapple') }

  package SpicyPizzaBuilder;

  use Moose;
  with 'PizzaBuilder';

  sub build_dough { shift->pizza->dough('pan baked') }
  sub build_sauce { shift->pizza->sauce('hot') }
  sub build_topping { shift->pizza->topping('pepperoni+salami') }

  package Waiter;

  use Moose;

  has 'pizza_builder' => (is=>'rw', does=>'PizzaBuilder');

  sub pizza { shift->pizza_builder->pizza }

  sub construct_pizza {
    my ($self) = @_;
    $self->pizza_builder->$_ for (qw/
      build_dough build_sauce build_topping/);
  }

}

ok my $waiter = Waiter->new;
ok my $hawaiian_pizza_builder = HawaiianPizzaBuilder->new;
ok my $spicy_pizza_builder = SpicyPizzaBuilder->new;

for($waiter) {
  $_->pizza_builder($hawaiian_pizza_builder);
  $_->construct_pizza;
}

is $waiter->pizza->sauce, 'mild';

for($waiter) {
  $_->pizza_builder($spicy_pizza_builder);
  $_->construct_pizza;
}

is $waiter->pizza->sauce, 'hot';

done_testing;