While developing a debugging aid, I stumbled across some untie behavior that seemed odd until pondered for a bit (leading to a "d'oh!" moment). Here is a stripped-down example. Can you predict what this script will print? 

use strict;

package Object;

sub new {
  bless {}, "Object"
}

sub foo { "ObjectFoo\n" }

package Tied;

sub TIESCALAR {
    my $class = shift;
    my $o = shift;
    bless \$o, $class;
}

sub FETCH {
    my $self = shift;
    print "<fetch>\n";
    $self
}

sub foo { "TiedFoo\n" }

package main;

my $o = new Object();
print $o->foo();

tie $o, 'Tied';
print $o->foo();

untie $o;
eval { print $o->foo() };
print "NoFoo\n" if $@;

[download]

Replies are listed 'Best First'.
Re: The aftermath of an untie
by herveus (Prior) on Oct 02, 2001 at 07:30 UTC
    Howdy!

    Under 5.004_04, I was able to strip this down even further and get the same output from the untie. 

    #!/bin/perl -w
use strict;

package Tied;

sub TIESCALAR
{
        my $class = shift;
        my $o = shift;
        bless \$o, $class;
}

sub FETCH
{
        my $self = shift;
        print "<fetch>\n";
        $self;
}

sub foo {"TiedFoo\n";}

package main;

my $o;
tie $o, 'Tied';
print $o->foo();

untie $o;
eval { print $o->foo() };
print "NoFoo\n" if $@;

    [download]

    In the end, $o was still tied.

    yours,
    Herveus

[reply]
[d/l]
      In the end, $o was still tied.

      Ah, but it isn't. $o is still associated with Tied, but the tie itself has been undone, as evidenced by the absense of a <fetch> message from the final invocation of $o->foo().

      That's the oddity I've noticed about untie -- the association with the Tied class is still there (i.e., the variable is still blessed), even though the variable is no longer tied. I have yet to find this behavior documented.

[reply]
[d/l]
[select]

Back to Meditations