Luau vectors

[setzer22]

I'm testing the new Luau support for native vectors in 0.8.0-beta.2. I can see the mlua::Value vector type and I've succesfully been able to pass a vector from Rust to Lua like so:

let lua = Lua::new();
let x: mlua::Function = lua
    .load("return function(v) print(v) end")
    .call(())
    .unwrap();
x.call::<_, ()>(mlua::Value::Vector(1.0, 2.0, 3.0));

But I can't create native vectors on the Lua side. The documentation suggests it's vector(1,2,3), but it doesn't seem to be working. Calling return vector(1,2,3) in Lua code tells me I'm trying to call a nil table (vector).

[khvzak]

The constructor indeed is not provided by Luau, you need to do something like:

    let globals = lua.globals();
    globals.set(
        "vector",
        lua.create_function(|_, (x, y, z)| Ok(Value::Vector(x, y, z)))?,
    )?;

[khvzak]

Probably I'll register vector(x,y,z) function in mlua when creating Luau state to make it even faster (as it never fails).

[setzer22]

Ah, for sure! I'd be very interested in something like that.

Actually, is there a way for me as an mlua user to register these kind of infallible functions that are supposed to be called very frequently? I'm thinking of exposing things like noise functions and it would be nice if they had the least overhead possible.

[khvzak]

Generic way is use Lua::create_c_function
It creates a a Lua/C function with zero overhead. However the ffi module is not yet published so you need to add lua C functions manually (via extern "C" block). They are available in Lua manual.
I plan to publish ffi module as well for external use.

[khvzak]

@setzer22 you could try the new beta.3 with native vector() constructor support (it should be fast).

[setzer22]

Thanks! I made a quick test it and it seems to be working nicely 😄 Not a significant difference on my (completely improvised and not very scientific) benchmarks, but I guess that's to be expected with branch prediction. Still, nice to have the native constructor in :)