in reply to getting 2 things done at once with Class::Base

This technique is heavily used in DBI internals. Look at any DBD and you'll see lots of things like: 
return $dbh->set_err(
    $DBI::stderr, "Invalid attribute '$attrib'"
);

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which sets the error to be acted on by RaiseError or PrintError or called explicitly with $h->errstr() and then returns undef.

In Section Meditations