Hi there, welcome to the monastery!

Couple little typos in your code that you can see below. The main one is that you forgot the $ sigil on the doc-> in the print statements:

use Class::Struct;

struct Document => {
    fileid  => '$',
    filename => '@',
    tags => '@'
};

my $doc = Document->new(
        fileid => 2,
        filename => [qw(a b c)],
        tags => [qw(d e f)]
);

print "File ID:  ", $doc->fileid, "\n";
print "Filename: ", @{$doc->filename}, "\n";
print "Tags:     ", @{$doc->tags}, "\n";
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Having looked at Class::Struct a bit, I can't say there is much here to recommend it anymore. A more current recommendation would be to use Moo (or Moose) for these features and more. Here is a posting from quite some time back from a more seasoned monk with a comparison.