Forbid breaking encapsulation of an object

gistfile1.txt

package Foo;
use overload '%{}' => sub {
    my ( $package ) = caller;
    if ( !$package->isa( __PACKAGE__ ) ) {
        require Carp;
        Carp::cluck( "Use a method instead!" );
    }
    return $_[0];
};
sub new { return bless { foo => 'bar' }, __PACKAGE__ }
sub foo { return shift->{foo} }

package main;
use v5.16;
my $foo = Foo->new;
say $foo->foo;
say $foo->{foo};