Hi everyone, I'm new to Rust, but I don't understand why PhantomData helps the following code compile. However, when I directly impl F, even though I've already set a constraint for P, it doesn't compile successfully? //impl<F, P> TSystem for F // ❌ ERROR impl<F, P> TSystem for PhantomSystem<F, P> // ✅ OK !? where F: Fn(P), P: TSystemParam + 'static, { fn run(self) { (self.0)(P::new()); } //fn run(self) { (self)(P::new()); } } 1 post - 1 participant Read full topic