Tracking

Shipyard comes with built-in tracking for insertion, modification, deletion and removal.
deletion will store the component in the tracking info whereas removal gives it back immediately.
It can be noticed on SparseSet::delete vs SparseSet::remove signatures:

fn delete(&mut self, entity: EntityId) -> bool {}
fn remove(&mut self, entity: EntityId) -> Option<T> {}

Components can be deleted or removed but whole entities can only be deleted (at least for now, it's technically possible to return something but I digress).

Declaration

Tracking is set with the Component trait. You can set it to any single operation or use All to track everything.

struct Life(f32);
impl Component for Life {
    type Tracking = track::Modification;
}

// or with the proc macro

#[derive(Component)]
#[track(Modification)]
struct Life(f32);

Usage

When inside a workload you will get all tracking information since the last time this system ran.
Outside workloads you'll get information since the last call to clear_*.

Inserted or Modified

You can query inserted and modified components when iterating by calling inserted, modified or inserted_or_modified on a view before making the iterator. (*_mut versions also exist).

fn run(life: View<Life>, mut is_dead: ViewMut<IsDead>) {
    for (entity, life) in life.modified().iter().with_id() {
        if life.0 <= 0.0 {
            is_dead.add_component_unchecked(entity, IsDead);
        }
    }
}

Removed or Deleted

Removed and deleted cannot be used with iter but can be accessed with removed, deleted or removed_or_deleted methods on views.

Reset

Inside workloads tracking information doesn't need to be reset. You will always get the operations that happened since the last run of the system.

You can reset out of workload tracking info with:

• clear_all_inserted
• clear_all_modified
• clear_all_inserted_and_modified
• clear_all_removed
• clear_all_deleted
• clear_all_removed_and_deleted

You can also reset removed and deleted information older than some timestamp.

Use World::get_tracking_timestamp or AllStorages::get_tracking_timestamp to get a timestamp.
Then call clear_all_deleted_older_than_timestamp, clear_all_removed_older_than_timestamp or clear_all_removed_or_deleted_older_than_timestamp.