use List::Util qw(reduce);
use Data::Dumper;

my @c = (1, 2, 3, 4);
my %d;

reduce { $a->{$b} ||= {} } \%d, @c;
print Dumper \%d;

##</code><code>##

$VAR1 = {
          '1' => {
                   '2' => {
                            '3' => {
                                     '4' => {}
                                   }
                          }
                 }
        };

##</code><code>##

(reduce { $a->{$b} ||= {} } \%d, @c[0..$#c-1])->{$c[$#c]} = 42;
print Dumper \%d;

##</code><code>##

$VAR1 = {
          '1' => {
                   '2' => {
                            '3' => {
                                     '4' => 42
                                   }
                          }
                 }
        };