The posted code returned:

Undefined subroutine &threads::shared::_id called at math1.pl line 5.
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Testing is done with 5.8.4 on windows XP.

Update: The above code could be fixed like this:

use threads; #added
use threads::shared;

  my $var : shared;

  if (threads::shared::_id($var)) {#pass the var not the ref
      print("'\$var' is shared\n");
  }
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Couple of things:

1) Any chance this will be exported into a public method someday ?

2) FYI: When I tried directly testing a ref operator (e.g., threads::shared::_id(\@ary)), it choked. I had to explicitly assign the ref to another variable, then it reports shared (which is the important bit for me).

For the record, here's a bit more complete test:

use threads;
use threads::shared;

package Dweeble;

sub new {
    my $class = shift;
    
    my %obj : shared = (
        cow => 'bossy'
    );
    return bless \%obj, $class;
}

sub holycow {
    print "Holy Cow!\n";
}

1;

package main;

my $hope : shared = 27;

my @ary : shared = (1,2,3,4,5);

my $aryref = \@ary;

my %hash : shared = ( one => 1, two => 2 );

my $hashref = \%hash;

my $cow;

my $krelboin = Dweeble->new();

print "hope is ", (threads::shared::_id($hope) ? "shared\n" : "private
+\n");

print "cow is ", (threads::shared::_id($cow) ? "shared\n" : "private\n
+");

print "ary is ", (threads::shared::_id($aryref) ? "shared\n" : "privat
+e\n");

print "hash is ", (threads::shared::_id($hashref) ? "shared\n" : "priv
+ate\n");

print "krelboin is ", (threads::shared::_id($krelboin) ? "shared\n" : 
+"private\n");
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1) Any chance this will be exported into a public method someday?

Most likely not. However, it probably isn't going to go away either. It's still in the blead code.

Remember: There's always one more bug.