Perl中的奇数哈希表示

Question

I have a hash that has the following content, dumped via Data::Dumper :

$VAR1 = [
      0
    ];

What does that mean? I can´t seem to understand if that "0" is a key with nothing assigned to it or any other thing. Only clue is that I got this error below, which says a hash cannot be referenced by a zero string, is that right?

Can't use string ("0") as a HASH ref while "strict refs" in use at FOO.pm

The way this is assigned to an hash is obscure, since the code is restrict, but in some other cases, this same hash had something like

$VAR1 = [
          {
            'ExtraInfo->m_Fade_Notification_Timer' => 'RTPC',
            'ExtraInfo->m_FarEndNESlot' => '28 MHz',
            'ExtraInfo->m_Temperature_Ra2' => '',
            'ExtraInfo->m_Path' => '',
            'ExtraInfo->m_Radio_Terminal_Name' => 'ST01',

          }
        ];

Answer 1

There are no hashes involved. $VAR1 = [ 0 ]; means the dumped variable is a reference to an array with a single element consisting of the number zero.

Answer 2

You can check what type of reference it is with the ref() command. If it returns 'HASH' for that variable then you're safe to use it as a hash reference like you expect. If not then your incoming data isn't what you expect and you can raise an exception or handle it otherwise.

if (ref($data) eq 'HASH') {
    while (my ($key, $value) = each %{$data}) {
        ...
    }
} else {
    die "Unexpected data";
}

Or you could use ref() twice in the comparison, giving it the structure you want. That avoids coding specific string values:

if (ref($data) eq ref({})) {
    ...