#!/usr/bin/env perl -l

use strict;
use warnings;

use Data::Dump;

for (1..3) {
    my $ref1 = gimme();
    $ref1->[0]{box}{y}{z} = $_;
    $ref1->[0]{box}{w} = 'x' if $_ == 2;
    $ref1->[0]{box}{a}{d} = 4 if $_ == 3;
    trace($ref1);

    my $ref2 = gimme();
    trace($ref2);
}

sub gimme {
    [
        {   
            box => {
                a => { b => 2, c => 3 },
                y => {}
            }   
        }   
    ]
}

sub trace {
    my ($ref) = @_;

    print 'Tracing: ';
    print join ' -> ',
        $ref, $ref->[0], $ref->[0]{box}, $ref->[0]{box}{y};
    dd $ref;

    return;
}