Windows pitfall: Subroutine redefined with use Modul

[Brutha]

Hello fellows,

this is not a question, but a warning about an issue, which cost me a day. This is a Windows specific problem. Is that hint enough to solve the following?

After boiling down the needle-in-haystack problem and dropping all but the necessary lines, I have the following three files:

File Baseclass.pm

package Baseclass;
use strict;
use subclass1;

print "load Baseclass\n";

sub new  { 
    my $class = shift;
    return bless {},$class;
}
1;

File Subclass1.pm

package Subclass1;

use strict;
use warnings;

use base( "Baseclass" );

sub new {
    my $class = shift;
    return $self  = $class->SUPER::new(@_);
}
print "load Subclass1\n";
1;

File Bla.pl

use strict;
use warnings;
use Subclass1;

my $obj = Subclass1->new;
1;

Now run perl bla.pl and you get the following output:

Load Subclass1
load Baseclass
Subroutine new redefined at Subclass1.pm line 11.
Load Subclass1

Now, here comes the solution.

It is simple but not really obvious in the sense of visible. It is the letter 's' or should I say 'S'?
In file Baseclass.pm line 3 uses 'subclass1' instead of 'Subclass1' with capital letter. Perl sees two modules use Subclass1; and use subclass1;. Windows does not care about case and gives Perl the file Subclass1.pm both times.

Hope this helps somebody, save your day for better things.

[dada]

yes, this is a nasty one indeed. as we all know, Perl is case sensitive, but the Windows filesystem not. what happens here is that Perl stores information about the modules it has loaded in its %INC hash, and it ends up having two entries for Subclass1. if you add these lines at the end of the bla.pl script:

use Data::Dumper;
print Dumper(\%INC);

you'll see something like:

$VAR1 = {
          [...]
          'subclass1.pm' => 'subclass1.pm',
          [...]
          'Subclass1.pm' => 'Subclass1.pm',
          [...]
        };

so, the file is one but Perl sees (and loads) two modules. this could also pose serious problems with imported symbols, because when the case of the package name doesn't match, Perl loads the .pm file but doesn't export anything, as in:

use fIlE::SpEc qw(catfile); # note the wrong case

$x = File::Spec->catfile('a', 'b', 'c'); # this works
$x = catfile('a', 'b', 'c'); # this croaks

this is even more unobvious, because the error goes unnoticed until you try to use something that's exported from the module.

unfortunately, Perl can't possibly catch this sort of errors, so you have to watch your case. one possible solution (for the typo-prone individuals :-) could be to always cut & paste the use line from the SYNOPSIS found in the module documentation.

[bart]

Is that hint enough to solve the following?

It's all I needed to know. tye has a nice module patch here, which would trap this when it happens.

Universally unimportant and overused

[Brutha]

Thanks for that great hint. tye's patch (Universally unimportant and overused) looks like a must for W32 Perl

My node was really intended as a reminder. The examples are simple to analyze, but a real life project with dozens of files does not shout "Hello, it's Windows!". When you have forks, file permissions, shell escapes etc you immediatly grab your printout of perlport, but not if you search for coding, cut and paste etc mistakes.

[Aragorn]

This is described in perlport: Don't use filenames which are different only in case.

Arjen