The excitement of running parallel may cause us to forget, ah yes, simply let Perl be Perl. The P::FM documentation provides a scalar example. That is send a scalar ref, de-ref as such in the run_on_finish callback. Ditto for array or hash.

$pm->finish(0,\$scalar);  # or
$pm->finish(0,\@array);   # or
$pm->finish(0,\%hash);
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$pm -> run_on_finish (
    sub {
        my ($pid, $exit_code, $ident, $exit_signal, $core_dump, $data_
+ref) = @_;

        if (defined($data_ref)) {
            my $scalar = ${$data_ref};  # or
            my @array  = @{$data_ref};  # or
            my %hash   = %{$data_ref};
        }
    }
);
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