Wow, that trait feature is great. I've been eagerly waiting for that one for a long time. Thank you to everyone who made that possible.
this post was submitted on 03 Apr 2025
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Rust
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If a trait has a supertrait you can coerce a reference to said trait object to a reference to a trait object of the supertrait
As someone that just started learning Rust: wha?
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.