Lifetimes mismatch

help
1

Hi Rustaceans,
my first question is which these two types? Either I'm blind or rustic hiding something from me. If it says two which type is the second?

error[E0623]: lifetime mismatch
  --> src/renderer/src/lib.rs:57:14
   |
48 | fn ray_color(ray: &Ray, world: &World, depth: u32, rng: &mut rand::rngs::SmallRng) -> Color {
   |                                ------
   |                                |
   |                                these two types are declared with different lifetimes...
...
57 |     if world.hit(ray, 0.001, f32::INFINITY, &mut rec) {
   |              ^^^ ...but data from `world` flows into `world` here
2

I agree the error message is confusing. How is the World type declared?

3

Here is the World struct

struct World<'a> {
    pub(crate) objects: Vec<Arc<dyn Hittable<'a>>>
}

pub trait Hittable<'obj>: Send + Sync {
    fn hit(&'obj self, ray: &Ray, t_min: f32, t_max: f32, rec: &mut HitRecord<'obj>) -> bool;
}

impl<'obj> Hittable<'obj> for World<'obj> {
    ...
}

let mut world = Arc::new(World::new())
..
fn render(......, world: Arc<World<'static>) {
     ...
    ray_color(..., world: &World)
}

The problem seems to be in line 57.
world.hit takes &'obj self which is less than 'static

4

Ok I found the source of issue. I shouldn't put a lifetime on the Hittable and World structs, instead the 'obj lifetime should go to the function definition:

fn hit<'obj>(...)

The original error message is confusing indeed.

5

Could you come up with a minimized repro in the playground and file a diagnostics ticket in the repo? It'd be nice to make this less confusing.

6

I wish I could, I went ahead and tried to reproduce, but got a ton of other unrelated errors. :frowning:

7

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