Announcing Rust 1.86.0

Basically, you can generalize your trait types into their parent (super) traits for situations when functionality is specific to those supertrait objects.

As an example, if you have a trait CanBark and it is a super trait for the trait IsDog, you can coerce your references of &dyn IsDog into a &dyn CanBark. You can then work with other trait types that share a super trait.

    
trait CanBark {
    fn bark(&self);
}
trait IsSeal: CanBark { }
trait IsDog: CanBark { }

fn bark_as_group(barkers: &Vec<&dyn CanBark>) {
    for barker in barkers {
        barker.bark();
    }
}

let spot: &dyn IsDog = get_spot();
let seal: &dyn IsSeal = get_seal();
let barkers: Vec<&dyn CanBark> = Vec::new();
barkers.push(spot);  // coerced
barkers.push(seal);  // coerced
bark_as_group(&barkers);

  

At least, I hope this is possible now. If it's purely "you can return a coerced type from a function", that is less useful.