[noelwelsh]

ECS is basically a very simple relational database. There is no equivalent of foreign keys or other constraints between components. I can't say, for example, "every entity that has a location must also have an associated mesh". If I forget to add a component it's just a silent failure. Everything runs fine, just the expected result doesn't happen.

[giovannibonetti]

I wonder if a compile-time array-of-structs (AoS) to struct-of-arrays (SoA) transformation like the one done by Zig [1] could fix that issue.

[1] https://zig.news/kristoff/struct-of-arrays-soa-in-zig-easy-i...

[suby]

You can probably write runtime tests for this. Some system which queries for component Location, and then does an assert for each component that the associated entity also has a mesh.

Granted, this is annoying and not a particularly great solution, but it would serve to give you a reminder for when you forget. I don't mean to diminish from your overall point either, it's a valid and good one I think.

[noelwelsh]

Yeah, runtime checks are not very desirable.

I have this vague thought that Rust needs a different kind of type system.

Standard type systems[0] basically rely on references between values[1]. I seem to read about numerous Rust systems that don't use references for various reasons. Usually the borrow checker gets in the way or they want a different memory layout[2]. This makes me think that what's needed is a type system that allows constraints to be expressed between values without requiring a reference between them. I don't know what this type system looks like, though.

[0]: Rust's type system is a fairly standard type system from an academic POV. The novelty is that it's the first language with traction to use a linear / affine type system, but these are relatively well studied in academia.

[1]: The theory is not formulated this way, but the representation they compile into is a bunch of references.

[2]: ECS, as I understand it, is not a reaction to Rust's type system but an architecture driven by memory layout, parallelism, and breaking-out-of-OO-hierarchy concerns. However the net result is the same.

[spencerflem]

Totally agreed, like when using an int to reference into an array, there's no way to guarantee that the int won't be out of range, so it needs a check every time

Also no ideas here, but its fun to think about anyways

[pcwalton]

In theory this is what Bundles are for, though it's easy to not realize that there's a bundle for what you want to do.

I should note that this is a problem with most game engines, not something unique to Bevy. For example, Unity is infamous for requiring arcane combinations of components to avoid silent failures.