use warnings;
use strict;

my $struct = [
    {
        1 => 'a',
        2 => 'b',
    },
    [
        1,
        2,
        3,
    ],
    {
        3 => 'c',
        4 => 'd',
    },
];

thing($struct);

sub thing {
    my ($aref) = @_;

    for my $elem (@$aref){
        if (ref $elem eq 'ARRAY'){
            print "array:\n";
            print "$_\n" for @$elem;
        }
        elsif (ref $elem eq 'HASH'){
            print "hash:\n";
            print "$_ => $elem->{$_}\n" for keys %$elem;
        }
        else {
            die "element is not an allowed ref\n";
        }
    }
}