this post was submitted on 21 Dec 2023

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Announcing async fn and return-position impl Trait in traits (blog.rust-lang.org)

submitted 11 months ago by [email protected] to c/rust

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[–] [email protected] 6 points 11 months ago

Whoa, very cool! Can't wait for 1.75.

[–] [email protected] -1 points 11 months ago* (last edited 11 months ago)

-> impl Trait in public traits

That's a bummer. This works:

trait Base {
  fn op(&amp;self);
}
trait Child : Base {
  fn other_op(&amp;self);
}

trait A {
  fn some_fn(val: impl Base) {
    val.op();
  }
}

fn some_fn(val: impl Child) {
  val.op();
  val.other_op();
}

So it seems like returning an impl Child in a trait that binds impl Base should also work.

Hopefully this change means we'll see more of this kind of thing in the upcoming releases.