feat: Entity bit interpretation

benches/common/heavy_compute.rs

@@ -10,15 +10,6 @@ component! {
     velocity: Vec3,
 }
 
-#[derive(Copy, Clone)]
-struct Position(Vec3);
-
-#[derive(Copy, Clone)]
-struct Rotation(Vec3);
-
-#[derive(Copy, Clone)]
-struct Velocity(Vec3);
-
 pub struct Benchmark(World);
 
 impl Benchmark {

benches/common/simple_iter.rs

@@ -11,7 +11,7 @@ component! {
     velocity: Vec3,
 }
 
-pub struct Benchmark(World, Query<(Component<Vec3>, Mutable<Vec3>)>);
+pub struct Benchmark(World);
 
 impl Benchmark {
     pub fn new() -> Self {
@@ -27,8 +27,7 @@ impl Benchmark {
         batch.set(velocity(), repeat(Vec3::X)).unwrap();
 
         batch.spawn(&mut world);
-        let query = Query::new((velocity(), position().as_mut()));
-        Self(world, query)
+        Self(world)
     }
 
     pub fn run(&mut self) {

src/entity/mod.rs

@@ -104,6 +104,28 @@ impl Entity {
     pub fn kind(&self) -> EntityKind {
         self.kind
     }
+
+    /// Returns a bit representation of the entity
+    pub fn as_bits(&self) -> u64 {
+        let index = self.index as u64;
+        let gen = self.gen.get() as u64;
+        let kind = self.kind.bits() as u64;
+
+        (index << 32) | (gen << 16) | kind
+    }
+
+    /// Reconstruct an entity from its bit representation
+    pub fn try_from_bits(mut bits: u64) -> Option<Self> {
+        let kind = EntityKind::from_bits(bits as u16).unwrap();
+        bits >>= 16;
+
+        let gen = EntityGen::new(bits as u16).unwrap();
+        bits >>= 16;
+
+        let index = bits as u32;
+
+        Some(Entity { index, gen, kind })
+    }
 }
 
 #[cfg(feature = "serde")]
@@ -300,4 +322,14 @@ mod tests {
         assert_eq!(align_of::<Entity>(), 4);
         assert_eq!(size_of::<Option<Entity>>(), 8);
     }
+
+    #[test]
+    fn test_bitcasts() {
+        let mut store = EntityStore::new(EntityKind::COMPONENT);
+
+        let a = store.spawn("a");
+
+        let a2 = Entity::try_from_bits(a.as_bits()).unwrap();
+        assert_eq!(a, a2);
+    }
 }

src/fetch/mod.rs

@@ -4,7 +4,7 @@ mod component;
 mod component_mut;
 mod copied;
 mod entity_ref;
-pub mod expect;
+mod expect;
 mod ext;
 mod map;
 mod maybe_mut;
@@ -33,6 +33,7 @@ pub use component::*;
 pub use component_mut::*;
 pub use copied::*;
 pub use entity_ref::*;
+pub use expect::*;
 pub use ext::FetchExt;
 pub use map::Map;
 pub use maybe_mut::{MaybeMut, MutGuard};

src/system/context.rs

@@ -11,11 +11,8 @@ use crate::{
 use super::{input::ExtractDyn, SystemAccess, SystemData};
 
 /// A resource that can be shared between systems
-/// The difference between this and an `Arc<Mutex<_>>` is that this will be
-/// taken into consideration when multithreading in the schedule, and will as
-/// such not require locks.
 ///
-/// The implementation is an `Arc<AtomicRefCell>` and is thus cheap to clone
+/// Used for safe multithreaded scheduling
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
 pub struct SharedResource<T>(Arc<AtomicRefCell<T>>);