#!/usr/bin/env perl

use v5.14;
use Data::Dumper;

package FooFactory {
	use Moo;
	has name => (is => "ro", required => 1);
	our @known_attributes;
	sub build_foo {
		my $self = shift;
		my %params = @_;
		my %attrs;
		for (@known_attributes) {
			$attrs{$_} = $params{$_} if exists $params{$_};
		}
		'Foo'->new(%attrs, maker => $self);
	}
}

package Foo {
   use Moo;
	sub my_has {
		my ($attr, %spec) = @_;
		# Inform FooFactory of the new attribute
		# Note we're ignoring init_arg for this simple example.
		push @FooFactory::known_attributes, $attr;
		has($attr, %spec);
	}
	my_has foo   => (is => "ro");
	my_has bar   => (is => "ro");
	my_has baz   => (is => "ro");
	my_has maker => (is => "ro");
}

my $factory = 'FooFactory'->new(name => "Acme Inc");
my $obj = $factory->build_foo(bar => 42);

print Dumper($obj);