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I do have the following simple code:

my $TimeZone = $hCache->{'TimeZone'}; # Cache gets filled earlier my $DateTime = DateTime->now(); $DateTime->set_time_zone($TimeZone);

This code runs in an application server which is basically a long running perl process that accepts incoming network connections.

From time to time this applicationserver gets somehow "dirty", and the code above is printing the following error:

The 'name' parameter ("Europe/Berlin") to DateTime::TimeZone::new was a 'glob', which is not one of the allowed types: scalar at /srv/epages/eproot/Perl/lib/site_perl/linux/DateTime.pm line 1960.

When I try to debug the variable "$TimeZone" I'm getting no further details.

E.g.

print ref($TimeZone); # prints nothing (scalar?) print $TimeZone; # prints "Europe/Berlin"

The code works if I'm forcing the timezone to be a string again, like so:

my $TimeZone = $hCache->{'TimeZone'}; # Cache gets filled earlier my $DateTime = DateTime->now(); $DateTime->set_time_zone($TimeZone."");

My questions are:

  1. If 'glob' is not a reference, how can I debug the variable properly?
  2. How can I create a 'glob' variable? What is the syntax to it? I'm quite sure that my huge codebase has some accidents in it, but I don't know what to search for.
  3. Is there a way to 'monitor' the variable? Basically, getting a stacktrace if the variable changes

EDIT: 2023-04-13

With the use of ChatGPT I was able to resolve the problem. It turns out that perl's "constant folding" was causing the issue. Replacing the affected constants with sub MYCONSTANT { "MyValue" } resolved the issue by preventing "constant folding" for the relevant constants. The challenge was to actually find the correct constant this applies to.

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    ref(\$var) will return GLOB for a glob. For example, perl -e'$x = *STDOUT; CORE::say ref(\$x)' Commented Feb 27, 2020 at 23:35
  • Thanks. Do you know if the star (*) is always the way for creating GLOBs? Commented Feb 27, 2020 at 23:44
  • * is the sigil for globs. *foo means "the glob named foo in the current package", just like $x refers to the scalar named x. Commented Feb 28, 2020 at 0:04

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How can I create a 'glob' variable?

Glob, short for "typeglob" is a structure (in the C sense of the word) that contains a field for each type of variable that can be found in the symbol table (scalar, array, hash, code, glob, etc). They form the symbol table.

Globs are created by simply mentioning a package variable.

@a = 4..6; # Creates glob *main::a containing a reference to the new array.

Since globs are themselves packages variables, you can bring a glob into existence just by mentioning it.

my $x = *glob; # The glob *main::glob is created by this line at compile-time.

Note that file handles are often accessed via globs. For example, open(my $fh, '<', ...) populates $fh with a reference to a glob that contains a reference to an IO.

$fh # Reference to glob that contains a reference to an IO. *$fh # Glob that contains a reference to an IO. *$fh{IO} # Reference to an IO.

If 'glob' is not a reference, how can I debug the variable properly?

ref(\$var) will return GLOB for a glob.

$ perl -e'$x = *STDOUT; CORE::say ref(\$x)' GLOB

Is there a way to 'monitor' the variable?

Yes. You can add magic to it.

$ perl -e' use feature qw( say ); use Carp qw( cluck ); use Variable::Magic qw( wizard cast ); my $wiz = wizard( data => sub { $_[1] }, set => sub { cluck("Variable $_[1] modified"); }, ); my $x; cast($x, $wiz, q{$x}); $x = 123; # Line 14 ' Variable $x modified at -e line 9. main::__ANON__(SCALAR(0x50bcee23c0), "\$x") called at -e line 14 eval {...} called at -e line 14

More work is needed to detect if a hash or array changes, but the above can be used to monitor the elements of hashes and arrays.

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2 Comments

Maybe you can help or explain something to me further? I got an object... But out of nowhere Perl is converting the attributes to typeglobs (see screenshot). Do you happen to know any further details on Perl's object processing? Screenshot: server.xsigndll.com/typeglob-issue.png
@xsigndll: Ask a new question to ask a new question. Perl normally doesn't do this: include all the details (is any OO framework included?), the best way is to post a SSCCE.

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