I'm working on what I imagined would be a simple module to provide versioned access to files (this is something that VMS provides), but it seems I've run up against a challenging (to me) situation with opening files in a module, and passing the file handle back to the caller as open does.

Here's some code that demonstrates the problem:

#!perl

use strict;
use warnings;

use Extra;

{
    {
      open ( my $fh, '>', 'normal-open.txt' ) or
        die "1. Open failed: $!";
      defined $fh or die "1. Filehandle not defined";
      print $fh "Normal open works fine.\n";
      close ( $fh );
    }

    {
      Extra::open ( my $fh, '>', 'extra-open.txt' ) or
        die "2. Open failed: $!";
      defined $fh or die "2. Filehandle not defined";
      print $fh "Extra open works fine.\n";
      close ( $fh );
    }
}
[download]

And the Extra module is here:

package Extra;

use Symbol;

sub open
{
    my ( $fh, $direction, $filename ) = @_;
    
    $fh = Symbol::gensym;
    open ( $fh, $direction, $filename );
}

1;
[download]

The first block works fine, and the second block returns from, but the filehandle is undefined.

I had a good look at the code for File::Temp, and saw where it uses the call to Symbol::gensym for Perls before 5.6, so I tried adding that in. It makes no difference -- I'm using Perl 5.22.1 anyway.

My plan is to hook the call to open and seamlessly handle open a versioned file using the requested file name as a basis -- I've also tried using sysopen, without any success. There's some magic going on that I don't understand.

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