I see the big "do not use" message in the readme, but I was pointed here after asking for advice in the Amethyst Discord.

I've got a toy app that I'm trying to integrate with NCollide, where most entities will have a CollisionObjectHandle. I want to make sure that when those entities are deleted, the corresponding collision object is deleted from the CollisionWorld. That seems to be one of the things you aim to do with this project, but for NPhysics objects.

Unfortunately, it looks like the currently-implemented approach doesn't actually work.

When the entities are despawned, the sync_bodies_to_physics and sync_colliders_to_physics systems look up their respective handles from storage in order to remove them from the physics world... but by that point the handles are seemingly already deleted.

I modified the amethyst.rs example, adding a pair of systems to spawn and despawn a handful of balls: dylemma@d8160c3

The result:

Deleting entity Entity(5, Generation(1))
[ERROR][nphysics_ecs_dumb::systems::sync_bodies_to_physics] Missing body with id: 5
[ERROR][nphysics_ecs_dumb::systems::sync_bodies_to_physics] Missing body with id: 5
[ERROR][nphysics_ecs_dumb::systems::sync_colliders_to_physics] Missing collider with id: 5
Deleting entity Entity(6, Generation(1))
[ERROR][nphysics_ecs_dumb::systems::sync_bodies_to_physics] Missing body with id: 6
[ERROR][nphysics_ecs_dumb::systems::sync_bodies_to_physics] Missing body with id: 6
[ERROR][nphysics_ecs_dumb::systems::sync_colliders_to_physics] Missing collider with id: 6
Deleting entity Entity(7, Generation(1))
[ERROR][nphysics_ecs_dumb::systems::sync_bodies_to_physics] Missing body with id: 7
[ERROR][nphysics_ecs_dumb::systems::sync_bodies_to_physics] Missing body with id: 7
[ERROR][nphysics_ecs_dumb::systems::sync_colliders_to_physics] Missing collider with id: 7
...and so on

Should be able to just depend on nalgebra and specs