#!/usr/bin/perl
use strict;
package Foo;
sub new{
  my $class = shift;
  my $self = {
	      bar=>""
	     };
  bless $self,$class;
}

sub bar : lvalue {
  my $self = shift;
  if (@_) {
    # validate
    my $value = shift;
    if (ref($value)) {
      die "foo->bar must not be a reference!\n";
    }
    $self->{bar}=$value;
  }
  $self->{bar}
}

package main;
my $test = Foo->new;

# Use lvalue assignment
$test->bar = "Hello";
print $test->bar."\n";

# Use setter mode to verify data
$test->bar("There");
print $test->bar."\n";

# Use setter mode to verify data
$test->bar($test);
print $test->bar."\n";

__OUTPUT__
Hello
There
foo->bar must not be a reference!