Modify enum through &mut self

help
1

Hi !

I'm facing a problem I have never seen. I fail to reproduce it with minimal code reproduction. So, there is a part of the code below (you can find the whole source code here).

pub trait Physic: Material {
   // [...]
    fn set_position(&mut self, value: [f32; 2]);
   // [...]
}

#[derive(Archive, Deserialize, Serialize, Clone, Debug, PartialEq, Constructor)]
#[rkyv(compare(PartialEq), derive(Debug))]
pub struct Bullet {
    pub position: [f32; 2],
    pub tile: TileXy,
    pub region: RegionXy,
    pub forces: Vec<Force>,
}

#[derive(Archive, Deserialize, Serialize, Clone, Debug, PartialEq)]
#[rkyv(compare(PartialEq), derive(Debug))]
pub enum Projectile {
    Bullet(Bullet),
}

impl Physic for &Projectile {
   // [...]
    fn set_position(&mut self, value: [f32; 2]) {
        match self {
            Projectile::Bullet(bullet) => bullet.position = value,
        }
    }
   // [...]
}

Error is:

error[E0594]: cannot assign to `bullet.position`, which is behind a `&` reference
  --> crates/oc_projectile/src/lib.rs:68:43
   |
68 |             Projectile::Bullet(bullet) => bullet.position = value,
   |                                           ^^^^^^^^^^^^^^^^^^^^^^^ `bullet` is a `&` reference, so it cannot be written to

As I can see, bullet here is &Bullet. But, I expect &mut Bullet as I match from &mut self. I don't understand ...

Thanks in advance !

2

You're implementing Physic for &Projectile therefore you have &mut self == &mut &Projectile which cannot provide mutable access.

3

The problem is that you're implementing on a reference:

Implement the trait directly instead:

impl Physic for Projectile {
4

Oh ! Right. I implement for &T beacause I have a strange compile error in other side. But its another story ... Thanks !!