A generated entity component system.
The gecs crate provides a compile-time generated, zero-overhead ECS for simulations on a budget. Compared to other ECS libraries, gecs precompiles queries using known archetype configurations to achieve better performance with no upfront cost or caching overhead. Queries in gecs can be inspected and checked at compile-time in order to catch what would otherwise be bugs presenting only in tests or execution. This comes at the cost of requiring all archetypes to be declared at compile-time, so that adding or removing components at runtime to entities isn't currently possible (though hybrid approaches could fix this in the future).
Archetypes in gecs can be set to contain a fixed capacity of entities. If all of the archetypes in your world declaration are configured in this way, gecs will perform zero allocations after startup and adhere to a known and predictable memory overhead for constrained environments (e.g. servers on cloud instances). Attempting to create a new entity in a full archetype will simply report failure (no panics). Support for dynamically-sized archetypes with Vec-like storage behavior is planned for support at a later date but is not currently implemented.
All of the code that gecs generates in user crates is safe, and users of gecs can use #[deny(unsafe_code)] in their own crates. Note that gecs does use unsafe code internally to allow for compiler optimizations around known invariants (this is, in large part, the point of this library).
This library may be used under your choice of the Apache 2.0 or MIT license.