Misbehaving typeglob

Ovid has asked for the wisdom of the Perl Monks concerning the following question:

Can anyone tell me why the following prints out both SCALAR and CODE? What am I missing?

#!/usr/bin/perl -l

use strict;
use warnings;

{
    package Foo;
    sub bar {};
}

foreach my $type ( qw<SCALAR ARRAY HASH CODE IO FORMAT> ) {
    print $type if defined *Foo::bar{$type};
}
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I only want that to print CODE. How do I fix it?

Cheers,
Ovid

New address of my CGI Course.

Comment on Misbehaving typeglob Download Code

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Re: Misbehaving typeglob
by Errto (Vicar) on Oct 27, 2006 at 16:35 UTC

perlref

*foo{THING} returns undef if that particular THING hasn't been used yet, except in the case of scalars. *foo{SCALAR} returns a reference to an anonymous scalar if $foo hasn't been used yet. This might change in a future release.

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Re: Misbehaving typeglob
by grep (Monsignor) on Oct 27, 2006 at 17:01 UTC

{
    no strict qw/refs vars/;
    local $varname = 'bar';
    local $fullname = "Foo::$varname";
    foreach my $type ( qw<SCALAR ARRAY HASH CODE IO FORMAT> ) {      
        print $type if (defined *{$fullname}{$type} and !($type eq 'SC
+ALAR' and !defined($$fullname)) );
    }
}
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grep

One dead unjugged rabbit fish later

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[d/l]

Re: Misbehaving typeglob
by stvn (Monsignor) on Oct 27, 2006 at 20:43 UTC

I ran into this same problem in Class::MOP (more specifically Class::MOP::Package). IIRC the value it creates is always a reference to undef, so I just deal with it as a special case for SCALAR and check for the ref to undef. I figure that it still behaves appropriately in most use cases, which is ugly, but there is little else that can be done. Of course if you do find a solution, please let me know :)

-stvn

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Re: Misbehaving typeglob
by diotalevi (Canon) on Oct 28, 2006 at 02:48 UTC

Upgrade to bleadperl where SCALAR isn't autocreated. You can't avoid it on anything less than 5.9.3.

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