I should note that I assume you want 1 rabbit per wolf (which is how it should start). If you want more, some additional logic should be added:
```
double Predator::capacity() {
  double ret = 0;
  for (int i = 0; i != max_eats_; i++) {
    double add = hunts() ? 1 : 0;
    ret += add;
  }
  return ret;
}
```