I think this is about at the limit of length acceptability--~70 lines. It's taken from O'Reilly's Advanced Perl Programming, pp 143-144. It's an example of Tying arrays, in this case making a File into an array. It seems to be losing the value of the my variables $F_OFFSETS and $F_FILEHANDLE. Can anybody please explain why, or if Perl has changed since this 1997 example was done? Code: 
tie @lines, 'TieFile', 'just_lines';
print $lines[20];
exit;

package TieFile;
use Symbol;
#use strict;

my $F_OFFSETS    = 0;
my $F_FILEHANDLE = 1;

sub TIEARRAY {
    my ($pkg, $filename) = @_;
    my $fh = gensym();
    open ($fh, $filename) || die "Could not open file: $!\n";
    print "TIEARRAY:\$fh=$fh\n"; # correctly says it is a glob
    bless [ [0],
            $fh         # stores it here
          ], $pkg;
}

sub FETCH  {
    print "fetch:\$F_FILEHANDLE=$F_FILEHANDLE\n"; # F_FILEHANDLE has d
+isappeared!
    print "defined!\n" if defined ($F_FILEHANDLE);
    print "not defined!\n" if !defined ($F_FILEHANDLE);
    my ($obj, $index) = @_;
    my $rl_offsets = $obj->[$F_OFFSETS];
    my $fh = $obj->[$F_FILEHANDLE];
    # my $fh = $obj->[1];
    print "fetch:\$fh=$fh\n";
    print "fetch:\$rl_offsets=$rl_offsets\n";
    if ($index > @$rl_offsets) {
        print "reading_until\n";
        $obj->read_until($index);
    } else {
        seek ($fh, $rl_offsets->[$index], 0);
    }
    return (scalar<$fh>);
}

sub STORE {
    die "Sorry, cannot update file using package TieFile\n";
}
sub DESTROY {
    my ($obj) = @_;
    close ($obj->[$F_FILEHANDLE]);
}

sub read_until {
    my ($obj, $index) = @_;
    my $rl_offsets = $obj->[$F_OFFSETS];
    my $last_index = @$rl_offsets - 1;
    my $last_offset = $rl_offsets->[$last_index];
    my $fh = $obj->[$F_FILEHANDLE];
    print "read_until:\$fh=$fh\n";
    seek ($fh, $last_offset, 0);
    my $buf;
    while (defined($buf = <$fh>)) {
        $last_offset += length($buf);
        $last_index++;
        push (@$rl_offsets, $last_offset);
        last if ($last_index > $index);
    }
}

1;

[download]
And the output I get: 
TIEARRAY:$fh=GLOB(0x10011028)
fetch:$F_FILEHANDLE=
not defined!
fetch:$fh=ARRAY(0x1002e8bc)
fetch:$rl_offsets=ARRAY(0x1002e8bc)
reading_until
read_until:$fh=ARRAY(0x1002e8bc)
Not a GLOB reference at TieFile.pm line 56.

[download]

In reply to TIEARRAY example out of date? by ongaku

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