++{the idea}, but here's another WTDI.

package Fixed;
use Carp;
use strict;

sub TIESCALAR {
        my ($class, $value) = @_;
        croak "No value provided for new Fixed scalar" 
           unless defined $value;
        bless \$value, $class;
}
 
sub FETCH {
        return ${$_[0]};
}
 
sub STORE {
        croak "Illegal assignment to Fixed scalar";
}

package main;

tie my $v, "Fixed" => "32";
tie my $x, "Fixed" => "0";
tie my $str, "Fixed" => "my string";

print ">> $v\n";
$v++;
print ">> $v\n";
[download]

-- Frag.