#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

{   package Element;
    use Moo;

    has name => (is => 'ro');
    has active_container => (is => 'rw');
}


{   package Container;
    use Moo;

    has elements => (is => 'ro', default => sub { [] });

    sub add_elem {
        my ($self, $element) = @_;
        push @{ $self->elements }, $element
            unless grep $_ == $element, @{ $self->elements };
    }

    sub get_elem {
        my ($self, $name) = @_;
        my $elem = (grep $_->name eq $name, @{ $self->elements })[0];
        $elem->active_container($self);
        return $elem
    }
}


my $elem1 = 'Element'->new(name => 'one');
my ($cont1, $cont2) = map 'Container'->new, 1, 2;
$cont1->add_elem($elem1);
$cont2->add_elem($elem1);
$cont1 == $cont1->get_elem('one')->active_container and say 'ok';
$cont2 == $cont2->get_elem('one')->active_container and say 'ok';

##</code><code>##

my $e1 = $cont1->get_elem('one');
my $e2 = $cont2->get_elem('one');
$e1->active_container ne $e2->active_container or die;