code: public static function with(array $theseObjects): MapsObjectsByIdentity
      {
          $objects = [];
          $entityIds = [];
          foreach ($theseObjects as $id => $object) {
              $objects = IdentityMap::addTo($objects, (string) $id, $object);
              $entityIds[theInstanceIdOf($object)] = (string) $id;
          }
          return new self($objects, $entityIds);
      }
docs: Produces a new identity map that contains the objects.
  
  @param object[] $theseObjects The objects to add, as [id => object]
  @return MapsObjectsByIdentity The map of objects.