interclass constraints not working

[ElectronicBatman]

I have two classes with simple public members, when I provide constraints which define dependency between classes, I dont see any randomization
e.g.

#include <crave/ConstrainedRandom.hpp>
#include <crave/experimental/Experimental.hpp>
#include <boost/format.hpp>
#include <iostream>

using namespace crave;
class class_a : public crv_sequence_item {
 public:
 crv_variable<unsigned int> num;
 
  crv_constraint legal_num_class_C{ num() < 10 };

 class_a(crave::crv_object_name name = "class_a") {
    
 }
 void print(){
   std::cout<<" CLASS A num "<<num<<"\n";

 }
};

class class_b : public crv_sequence_item {
 public:
 crv_variable<unsigned int> powr;

 class_b(crave::crv_object_name name = "class_b") {
   
 }
 void print(){
   std::cout<<" CLASS B POW "<<powr<<"\n";

 }
};


int main(int argc, char* argv[]) {
  crave::init("crave.cfg");
  crave::set_global_seed(123456789);

  class_a a("a");
  class_b b("b");

  crv_constraint legal_pow_class_{ b.powr() == (1<<a.num()) };

  CHECK(a.randomize());
  CHECK(b.randomize());
  a.print();
  b.print();
}

I get values of num and powr as zero when printed
CLASS A num 0
CLASS B POW 0