#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my @arr = qw(aa bb cc dd ee ff);

sub build {
    my %hash;
    my $ref = \%hash;
    while (defined (my $element = shift @_)) {
        $ref = ($ref->{$element} = @_ ? {} : 0);
    }
    \%hash;
}
print Dumper build(@arr);

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
use Benchmark 'timethese';


timethese(
    100000, {
    'manual' => sub {
        my @arr = qw(aa bb cc dd ee ff);
        my %hash;
        my $ref = \%hash;
        while (defined (my $element = shift @arr)) {
            $ref = ($ref->{$element} = @arr ? {} : 0);
        }
        \%hash;
    },
    'eval_string' => sub {
        my $hoh;
        my @array = qw(aa bb cc dd ee ff);
        my %hash;
        my $eval_string = '$hoh->{' . (join '}{', @array) . '} = 0'; 
        eval "$eval_string";
        $hoh
    },
  }
);

##</code><code>##

Benchmark: timing 100000 iterations of eval_string, manual...
eval_string: 10 wallclock secs ( 9.31 usr +  0.05 sys =  9.36 CPU) @ 10683.76/s (n=100000)
    manual:  2 wallclock secs ( 2.07 usr +  0.01 sys =  2.08 CPU) @ 48076.92/s (n=100000)