Selective exporting of properties/methods

[Chris Dutton]

While thinking Eiffel-ish thoughts the other day, I began to wonder if 
Perl6's classes could go beyond the simple private/public/protected 
scheme by optionally allowing for a property or method to only be 
accessed by a certain set of classes.  For instance(as I understand 
Perl6 syntax):

class Foo {
        method hello is public {
                return "hello";
        }
        method world is public_to(Bar) {
                # is only public to objects of class Bar
                return "world";
        }
}

class Bar {
        method say_hello {
                # this works fine
                print Foo.new.hello, "\n";
        }
        method say_world {
                # as does this
                print Foo.new.world, "\n";
        }
}

class Baz {
        method say_world {
                # generates a run-time exception for trying to call a private method.
                print Foo.new.world, "\n";
        }
}