[WIP] Tracked Interface

[Aceeri]

todo:

• Remove TrackedStorage?
• Add ChangedStorage (FlaggedStorage + comparisons)
• Should the Tracked::Modified/Inserted/Removed be Join or BitSetLike?
• How to deal with &mut storage & storage.modified() together.

---

This change is 

[torkleyy]

How will this interact with #301 ?

[torkleyy]

A chapter about component metadata would be helpful after this is merged.

[Aceeri]

How will this interact with #301 ?

#301 will be closed after this is finished.

[torkleyy]

Thanks for the PR, I want to review in a few hours (if I don't forget it). Just a note, there's a little conflict with the changelog.

[torkleyy]

This is great, thank you so much! I have to take a closer look at the track module, the rest looks great.

---

Reviewed 1 of 5 files at r1, 5 of 9 files at r3, 2 of 5 files at r4.
Review status: 8 of 11 files reviewed at latest revision, 5 unresolved discussions, some commit checks failed.

---

examples/track.rs, line 26 at r4 (raw file):

    );
    fn run(&mut self, (entities, tracked): Self::SystemData) {
        if let None = self.modified_id {

This should use match and return the reader id.

---

src/lib.rs, line 219 at r4 (raw file):

pub use shred::AsyncDispatcher;

pub use storage::{BTreeStorage, Capacity, DefaultCapacity, DenseVecStorage, DistinctStorage,

Yes, we do need to organize this.

---

src/storage/flagged.rs, line 76 at r4 (raw file):

///#        let condition = true;
///         for (entity, _) in (&*entities, &comps.check()).join() {
///             if condition { // check whether this component should be modified.

Should this use the restricted storage?

---

src/storage/flagged.rs, line 115 at r4 (raw file):

    fn default() -> Self {
        FlaggedStorage {
            modified: EventChannel::with_capacity(Cap::Modify),

I don't agree with this strategy, but don't have a constructive suggestion at the moment.

---

src/storage/track.rs, line 192 at r4 (raw file):

/// Clears and populates a structure with an event channel's contents.
pub trait Populate<T> {

Do we really need to export this?

---

Comments from Reviewable