# stecs - static compiler-checked ECS\*

This is an experimental ECS library intended to be more compiler-friendly. Archetypes are static, and queries are checked at compile-time. For an introduction into the idea, see [this blogpost](https://nertsal.github.io/blog/so-i-wrote-my-own-ecs/).

This library attempts to bridge the gap between
- compile-time guarantees, that are one of the important points of Rust;
- performance benefits of [SoA](https://en.wikipedia.org/wiki/AoS_and_SoA) (Struct of Array);
- and ease of use of ECS libraries

**\*Note**: technically this library likely does not qualify as a proper ECS.
What this library actually is, is a generalized SoA derive
(For an example of a non-general one, see [soa_derive](https://crates.io/crates/soa_derive) or [soa-rs](https://crates.io/crates/soa-rs/)).

This library contains and also generates snippets of unsafe code to support mutable querying.
It could be avoided by using lending iterators, but they are much less convenient to use in for-loops.
However, if possible, the goal is for the library to contain no unsafe code.

See [crate documentation](https://docs.rs/stecs/) for more information. And see [Horns of Combustion](https://github.com/Nertsal/horns-of-combustion) for an example of a game using this library.

## Example

[See more examples here](examples/).

```rust
use stecs::prelude::*;

#[derive(SplitFields)]
struct Player {
    position: f64,
    health: Option<i64>,
}

struct World {
    players: StructOf<Vec<Player>>,
}

fn main() {
    let mut world = World { players: Default::default() };
    world.insert(Player {
        position: 1,
        health: Some(5),
    });

    for (pos, health) in query!(world.players, (&position, &mut health.Get.Some)) {
        println!("player at {}; health: {}", position, health);
        *health -= 1;
    }
}
```

## Similar projects

### [gecs](https://crates.io/crates/gecs)

`gecs` provides similar functionality with static archetypes and checked queries. It has a more conventional to ECS layout, where all archetypes get queried at the same time. 

### Similar to some parts of this library:
- [soa-rs](https://crates.io/crates/soa-rs/)
- [soa_derive](https://crates.io/crates/soa_derive)
- [soa-vec](https://crates.io/crates/soa-vec)