class ComponentManager extends Manager {
 Bag<Bag<Component>> _componentsByType;
 Bag<Entity> _deleted;

 ComponentManager() : _componentsByType = new Bag<Bag<Component>>(),
                      _deleted = new Bag<Entity>();

 void initialize() {}

 void _removeComponentsOfEntity(Entity e) {
   _forComponentsOfEntity(e, (components, typeId) {
     components[e.id]._removed();
     components[e.id] = null;
   });
   e._typeBits = 0;
 }

 void _addComponent(Entity e, ComponentType type, Component component) {
   int index = type.id;
   _componentsByType._ensureCapacity(index);

   Bag<Component> components = _componentsByType[index];
   if(components == null) {
     components = new Bag<Component>();
     _componentsByType[index] = components;
   }

   components[e.id] = component;

   e._addTypeBit(type.bit);
 }

 void _removeComponent(Entity e, ComponentType type) {
   if((e._typeBits & type.bit) != 0) {
     int typeId = type.id;
     _componentsByType[typeId][e.id]._removed();
     _componentsByType[typeId][e.id] = null;
     e._removeTypeBit(type.bit);
   }
 }

 Bag<Component> getComponentsByType(ComponentType type) {
   int index = type.id;
   _componentsByType._ensureCapacity(index);

   Bag<Component> components = _componentsByType[index];
   if(components == null) {
     components = new Bag<Component>();
     _componentsByType[index] = components;
   }
   return components;
 }

 Component _getComponent(Entity e, ComponentType type) {
   int index = type.id;
   Bag<Component> components = _componentsByType[index];
   if(components != null && components.isIndexWithinBounds(e.id)) {
     return components[e.id];
   }
   return null;
 }

 Bag<Component> getComponentsFor(Entity e, Bag<Component> fillBag) {
   _forComponentsOfEntity(e, (components, _) => fillBag.add(components[e.id]));

   return fillBag;
 }

 void _forComponentsOfEntity(Entity e, void f(Bag<Component> components, int index)) {
   int componentBits = e._typeBits;
   int index = 0;
   while (componentBits > 0) {
     if ((componentBits & 1) == 1) {
       f(_componentsByType[index], index);
     }
     index++;
     componentBits = componentBits >> 1;
   }
 }

 void deleted(Entity e) => _deleted.add(e);

 void clean() {
   _deleted.forEach((entity) => _removeComponentsOfEntity(entity));
   _deleted.clear();
 }
}