A low-boilerplate, high performance archetype based ECS.

Pros:

• Archetypes
• Low boilerplate
• MIT Licensed

Cons:

• Widespread use of 16-bit values is begging for overflows
• Some O(N) patterns I dislike, fortunately with small C.
• Not MIRI friendly in even the most trivial of examples.
• Difficult-to-vet unsafe code, strongly suspect some unsound.
• Omnipresent low-value logging
• Tons of dependencies (89)

0.1.1

crev
thoroughness	medium
understanding	low (thanks to use of unsafe)
rating	negative

File	Rating	Notes
benches/allocation_stress.rs	+1	No global side effects, no black box use...?
benches/pos_vel.rs	+1	No global side effects, no black box use...?
examples/hello_world.rs	+1
src/borrows.rs	+1	API lock design concerns me... and I suspect this relies on stable_drop_order to avoid aliasing violations.
src/lib.rs	-1	Difficult to vet unsafe. Some O(N) and overflow concerns.
src/query.rs	-1	Difficult to vet unsafe.
src/storage.rs	-1	Tons of difficult-to-vet UnsafeCell use that leaks some of it's unsafety out to other files.
tests/query_api.rs	+1
tests/world_api.rs	+1
.cargo_vcs_info.json	+1
.cargo-ok	+1
.gitignore	+1
.travis.yml	+1	caching cargo might be a bad idea IME
bench.png	+1
Cargo.toml	+1	MIT
Cargo.toml.orig	+1	MIT
LICENSE	+1	MIT
readme.md	+1

Other	Rating	Notes
unsafe	-1	Lots of hard to reason about unsafe.
miri	-1	Trivial use chokes up miri.
fs	+1
io	+1
docs	+1
tests	+1

src/borrows.rs

Line	What	Notes
17	Borrow::aquire_read	Possible race condition source. Attempts to increment if >= 0. Theoretically could livelock if sufficiently contested, shouldn't in practice.
33	Borrow::aquire_write	Possible race condition source. Attempts to go from 0 => -1.
43	Drop for Borrow	+1
57	Borrowed	Safe from aliasing violations by virtue of stable_drop_order ? Cannot drop Borrow before value lifetime has ended.
92	PartialEq for Borrowed	'b lifetime unused...?
98	Eq for Borrowed	'b lifetime unused...?
128	BorrowedMut	Safe from aliasing violations by virtue of stable_drop_order ? Cannot drop Borrow before value lifetime has ended.
177	BorrowedSlice	Safe from aliasing violations by virtue of stable_drop_order ? Cannot drop Borrow before value lifetime has ended.
220	BorrowedMutSlice	Safe from aliasing violations by virtue of stable_drop_order ? Cannot drop Borrow before value lifetime has ended.
269	BorrowedIter	Safe from aliasing violations by virtue of stable_drop_order ? Cannot drop Borrow before value lifetime has ended.
EOF

src/lib.rs

Line	What	Notes
1	Lib doc comments	+1
254	WorldId	Only 16-bit world IDs? I could see this overflowing in practice, especially if using the advertized ability to stream stuff in.
264	ArchetypeId	Only 16-bit chunk IDs? Also, poor alignment.
281	Entity	Standard dual generation index, I approve... although hot entity IDs could overflow in practice?
310	Universe::logger	Not entirely sure I'm a fan of this.
365	ComponentIndex & friends	These Indexes should be used earlier when defining WorldId etc....
409	impl EntityBlock	+1
431	EntityBlock::in_range	Slightly bogus u32 cast - EntityBlock::new should enforce u32 size if you want a u32 len...
498	impl EntityAllocator	Full of O(N/1024) operations that could be O(1). Chunking is fine, but this really should abuse the fact that BLOCK_SIZE is constant more instead of looping.
517	EntityAllocator::create_entity	A better allocation strategy (IMO) would be to always start with the block we last allocated from. Will have degenerate behavior if we're constantly freeing/allocating from the first block.
625	World::merge doc comment	Concerning, implies API is unsound
638	World::merge	unsafe { ... } - I think this might be sound thanks to &mut self implying we have exclusive access to self.archetypes[?].chunks()[?].entities()
719	World::insert	unsafe { ... } - I think this might be sound thanks to &mut self implying we have exclusive access to self.archetypes[?].chunks()[?].entities()
720	World::insert	unsafe { ... } - I think this might be sound thanks to &mut self implying we have exclusive access to self.archetypes[?].chunks()[?].entities()
805	World::entity_data_mut	unsafe { ... } - I think this might be sound thanks to &mut self implying we have exclusive access to self.archetypes[?].chunks()[?].entities()
841	World::prep_archetype	unsafe { ... } - Probably sound - index should be valid - but why not just `.map(
1016	EntitySource for IterEntitySource	unsafe { ... } - I think this might be sound thanks to &mut Chunk implying we have exclusive access to chunk.entities()
EOF

src/query.rs

Line	What	Notes
*	PhantomData	Frequently used when T is already used in the struct, I'm concerned I'm missing something.
196	impl View for (...) validate()	unsafe { ... } - 0 <= i < j < types.len(), so both calls to get_unchecked should be sound.
276	std::ops::Not for Passthrough	Oooh, operator overloading abuse. Probably fine?
1065	impl Iterator for ZipEntities next	unsafe { ... } - Sketchy, assumes data.len() <= entities.len() and that's not a particularly trivial assertion to prove.
1088	ChunkView::entities	unsafe { ... } - NFI if this is sound or not.
EOF

src/storage.rs

Line	What	Notes
19	StorageVec	UnsafeCell! Oh no.
39	unsafe fn StorageVec::data_mut(&self)	Because this doesn't take &mut self, this forces the caller to enforce borrow checking manually.
47	ComponentStorage::remove for StorageVec	unsafe { ... } - I think this might be sound thanks to &mut self
52	ComponentStorage::len for StorageVec	unsafe { ... } - Unsound? It's not clear what, if anything, ensures len() isn't being mutated by another borrower.
104	unsafe fn Chunk::entities_unchecked	Because this doesn't take &mut self, this forces the caller to enforce borrow checking manually.
126	unsafe fn Chunk::entity_data_unchecked	+1?
141	unsafe fn Chunk::entity_data_mut_unchecked	Ditto.
157	Chunk::entity_data	unsafe { ... } - Unsound? "Locks" via borrow types after constructing &T, which is too late.
174	Chunk::entity_data_mut	unsafe { ... } - Unsound? "Locks" via borrow types after constructing &mut T, which is too late.
199	Chunk::shared_data	unsafe { ... } - NFI if this is sound or not. Haven't groked why SharedComponentStore is UnsafeCell or what protects it, if anything.
212	Chunk::remove	unsafe { ... } - I think this might be sound thanks to &mut self
EOF

Miri Example

use legion::prelude::*;

[test] // PREPEND YOUR OWN POUND SIGN
fn test() {
    let universe = Universe::new(None);
    let mut world = universe.create_world();
    world.insert_from((), vec![(1i32,)]);
}

rustup toolchain install nightly-2019-09-11
rustup component add miri --toolchain=nightly-2019-09-11
cargo +nightly-2019-09-11 miri test

error[E0080]: Miri evaluation error: trying to reborrow for SharedReadWrite, but parent tag <126591> does not have an appropriate item in the borrow stack
    |
    = note: inside call to `<legion::IterEntitySource<std::vec::IntoIter<(i32,)>, (i32,)> as legion::EntitySource>::write` at C:\Users\Mike\.cargo\registry\src\github.com-1ecc6299db9ec823\legion-0.1.1\src\lib.rs:716:29
    = note: inside call to `legion::World::insert::<(), legion::IterEntitySource<std::vec::IntoIter<(i32,)>, (i32,)>>` at C:\Users\Mike\.cargo\registry\src\github.com-1ecc6299db9ec823\legion-0.1.1\src\lib.rs:689:9
note: inside call to `legion::World::insert_from::<(), std::vec::Vec<(i32,)>>` at src\lib.rs:7:5
    --> src\lib.rs:7:5
     |
7    |     world.insert_from((), vec![(1i32,)]);
     |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: inside call to `test` at src\lib.rs:4:1
    --> src\lib.rs:4:1
     |
4    | / fn test() {
5    | |     let universe = Universe::new(None);
6    | |     let mut world = universe.create_world();
7    | |     world.insert_from((), vec![(1i32,)]);
8    | | }
     | |_^

TIL

• TypeId::of::<T>()