Any Way to Do This Without Specialization?

help
1

I'm pretty certain this is the exact use-case for specialization, but can any super-smart person find a way to do this without specialization?

I'm trying to find a way to automatically implement Component for any Rust type without boilerplate, but still allow explicitly implementing Component manually. Related to the bevy stable TypeId issue.

use std::collections::hash_map::DefaultHasher;
use std::hash::{Hash, Hasher};
use std::any::TypeId;

struct Component1;
struct Component0;

impl Component for Component0 {
    fn id() -> u64 {
        0
    }
}

trait Component {
    fn id() -> u64;
}

impl<T: 'static> Component for T {
    fn id() -> u64 {
        let mut hasher = DefaultHasher::new();
        let id = TypeId::of::<T>();
        id.hash(&mut hasher);
        hasher.finish()
    }
}

fn main() {
    dbg!(Component1::id());
    dbg!(Component0::id());
}

(Playground)

Errors:

   Compiling playground v0.0.1 (/playground)
error[E0119]: conflicting implementations of trait `Component` for type `Component0`:
  --> src/main.rs:18:1
   |
8  | impl Component for Component0 {
   | ----------------------------- first implementation here
...
18 | impl<T: 'static> Component for T {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `Component0`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0119`.
error: could not compile `playground`.

To learn more, run the command again with --verbose.
2

Ah, nevermind, found a better solution for the particular application:

https://github.com/bevyengine/bevy/issues/32#issuecomment-673784868