$my_object_of_class_A =~ qclassB/$string/

##</code><code>##

use warnings; use strict; 

sub len_3mult {
        my($s) = @_; 
        0 == length($s) % 3;
}
my $len_3mult = qr/\A(.*)\z(?(?{ len_3mult($^N) })|(?!))/s;  

for my $s (qw"my his your their socket connect protocol terminate") {
        if ($s =~ /$len_3mult/) {
                print "<<$s>> matches\n";                                          
        } else {
                print "<<$s>> does not match\n"
        }
}