use 5.016; # For __SUB__, or pre-declare $grep and use $grep->() syntax

    sub ref_grep(&$) {
        my ($wanted, $ref) = @_;
        my $seen = {}; # Refs we've already seen (avoid circular refs)
        my @found;     # Result list
        
        my $grep = sub {
            my ($ref, $path) = @_;
            return if ref $ref and $seen->{$ref}++;
            { $_ = $ref; push @found, $path if $wanted->() }
            for (ref $ref) {
                when ('HASH') {
                    __SUB__->($ref->{$_}, $path."->{$_}") for sort keys $ref;
                }
                when ('ARRAY') {
                    __SUB__->($ref->[$_], $path."->[$_]") for sort keys $ref;
                }
            }
        };
        $grep->($ref, '');
        return @found;
    }