package Test;

sub new {
    my ($class, $foo, $bar) = @_;
    return bless { 
            foo => $foo
            } => ref($class) || $class;
}

sub foo : lvalue { $_[0]->{foo} }

package main;

my $test = Test->new("foo");
print $test->foo, "\n";

$test->foo = "bar";
print $test->foo, "\n";

$test->foo =~ s/bar/baz/g;
print $test->foo, "\n";