use strict;
use warnings;
use feature 'say';

{
	package Tree;
	use Moose;
	has health_level => (
		is      => 'rw',
		isa     => 'Int',
	);
	
	sub grow_leaf {
		my $self = shift;
		Leaf->new(tree => $self); # pass $self on to child
	}
}

{
	package Leaf;
	use Moose;
	has tree => (
		is      => 'bare',
		handles => ['health_level'],
	);
}


my $t = Tree->new(health_level => 100);
my $l = $t->grow_leaf;

say $l->health_level;   # 100

$t->health_level(90);

say $l->health_level;   # 90