Note: Please read carefully; it's odd (unless I have tomatoes on my eyes)

I was changing a program of mine when it suddenly stopped to work as intended, and I failed to find the reason. Eventually I found it; please consider this Perl debugger session extract (Perl 5.18.2):

  DB<8> x $result
0  undef
  DB<9> c
main::receive_message(./syslogd.pl:1555):
1555:           $result = 1;
  DB<9> x $result
0  ARRAY(0x375cdb0)
   0  IO::Socket::INET=GLOB(0x2f8aa20)
      -> *Symbol::GEN3
            FileHandle({*Symbol::GEN3}) => fileno(6)
   1  SocketAddress=ARRAY(0x375d188)
      0  'v04:36766'
      1  'v04'
      2  36766
      3  ''
   2  '<22>May 23 10:22:07 v04 postfix/cleanup[22002]: F26AB68046: message-id=<1653294126.782e1e75c78c74d3@v04>'
  DB<10> n
main::receive_message(./syslogd.pl:1561):
1561:       $lc->verbose(3, "$me: returning " . Class::_format_undef($result));
  DB<10> x $result
0  undef

So in line 1555 $result will be set to 1 (inside an if-else block). Before $result is an ARRAY ref (as seeen). However after the line was executed (by n), the value of $result is undef, not 1 (right after the if-else block, thus a few lines later).

As the result will be returned, the caller sees the wrong result value and fails.

Unfortunately either me or Perl is heavily confused. Who can explain?

CodePudding user response：

The tomatoes fell of my eyes! (I'm providing this answer instead of deleting the question just in case someone will ever see a similar problem)

The code basically was:

sub receive_message($$$$;$)
{
    #...
    my $result;
    my $lc = $err_mh->log_config();

    if (defined(my $result = $lsa->receive(undef, MAXLEN, $flags))) {
        #...
        $result = 1;   # line 1555
    } else {
        #...
    }
    $lc->verbose(3, "$me: returning " . Class::_format_undef($result)); # line 1561
    return $result;
}

So the error was: "a my too much" (in the if).