This code shows that you were not that precise :-) (Update: See below reply from phaylon, sounds like I have misunderstood what he said, and that was my fault. I up voted both of his posts.)

use strict;
use warnings;
my $ref = {"a" => 1};
print $ref, "\n";
foo($ref);

sub foo {
    my $ref = shift;
    print $ref, "\n";
    $ref = { "all" => "new" };
    print $ref, "\n";
}
[download]

Run it, you will see that the first two print statements print the same addresses, but not the third one.