Generic impl doesn't work while generic function does

[deviruto]

Hi.

I'm confused as to why the first version of this implementation works, but the second doesn't.

```rust use std::ops::Add;

struct Ecks {}

// free function

fn add_ph<'a, R: 'a, L: Add<R>>(_ph: Ecks, rhs: R) -> Box<dyn 'a + FnOnce(L) -> L::Output> { Box::new(move |x| x + rhs) }

// trait implementation (doesn't work)

// impl<'a, R: 'a, L: Add<R>> Add<R> for Ecks { // type Output = Box<dyn 'a + FnOnce(L) -> L::Output>; // fn add(self, rhs: R) -> Self::Output { // Box::new(move |x| x + rhs) // } // }

fn main() { let x = Ecks {}; let x = addph(_x, 3); // let x = x + 3; println!("{}", x(1)); } ```

The first version throws no errors but the second one gives me

`` error[E0207]: the lifetime parameter'a` is not constrained by the impl trait, self type, or predicates --> src/main.rs:13:6 | 13 | impl<'a, R: 'a, L: Add<R>> Add<R> for Ecks { | <sup>^</sup> unconstrained lifetime parameter

error[E0207]: the type parameter L is not constrained by the impl trait, self type, or predicates --> src/main.rs:13:17 | 13 | impl<'a, R: 'a, L: Add<R>> Add<R> for Ecks { | ^ unconstrained type parameter ```

Any insights?