mid: use defined-or with `push' for uniqueness check

As shown recently in commit a05445fb400108e60ede7d377cf3b26a0392eb24
("config: config_fh_parse: micro-optimize"), the relying on
the return value of `push' and defined-or operators can avoid
modifying a the hash value scalar with an increment.

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/PublicInbox/MID.pm b/lib/PublicInbox/MID.pm
index 5aeffb8c..601f4c9b 100644
--- a/lib/PublicInbox/MID.pm
+++ b/lib/PublicInbox/MID.pm
@@ -119,7 +119,7 @@ sub uniq_mids ($;$) {
                         warn "Message-ID: <$mid> too long, truncating\n";
                         $mid = substr($mid, 0, MAX_MID_SIZE);
                 }
-                push(@ret, $mid) unless $seen->{$mid}++;
+                $seen->{$mid} //= push(@ret, $mid);
         }
         \@ret;
 }