sub onTick {
    our $x;
    # Initialize and associate $x with some external value
    foreach (@kabluther) {
        $x <op> $_->getSkookiness();
    }
    return $x;
}

##</code><code>##

sub onTick {
    our $x;
    # Initialize and associate $x with some external value
    foreach (@kabluther) {
        $_->getSkookiness( \$x );
    }
    return $x;
}

##</code><code>##

#! perl -slw
use strict;

package proxy;
my %flags;
sub TIESCALAR {
    my $self = bless \$_[1], $_[0]; 
    $flags{ $self } = 0; 
    $self 
}
sub FETCH { $flags{ $_[ 0 ] } |= 1; $_[0]; }
sub STORE { $flags{ $_[ 0 ] } |= 2; ${ $_[0] } = $_[1]; }
sub referenced {
    return ' :was read'             if $flags{ $_[ 0 ] } == 1;
    return ' :was written'          if $flags{ $_[ 0 ] } == 2;
    return ' :was read and written' if $flags{ $_[ 0 ] } == 3;
    return ' :was untouched';
}

package main;
sub readOnly { my $copy = $_[0] }
sub writeOnly{ $_[ 0 ] = 'written'; }
sub readThenWrite { my $copy = $_[0]; $_[ 0 ] = 'read & written'; }

our $x = 'some text';
my $o = tie my $proxy, 'proxy', $x;

print $x, $o->referenced;

readOnly $proxy;
print $x, $o->referenced;

writeOnly $proxy;
print $x, $o->referenced;

readThenWrite $proxy;
print $x, $o->referenced;

__END__
c:\test>tieProxy
some text :was untouched
some text :was read
written :was read and written
read & written :was read and written