trait_upcasting

The tracking issue for this feature is: #65991


The trait_upcasting feature adds support for trait upcasting coercion. This allows a trait object of type dyn Bar to be cast to a trait object of type dyn Foo so long as Bar: Foo.

#![allow(unused)] #![feature(trait_upcasting)] #![allow(incomplete_features)] fn main() { trait Foo {} trait Bar: Foo {} impl Foo for i32 {} impl<T: Foo + ?Sized> Bar for T {} let bar: &dyn Bar = &123; let foo: &dyn Foo = bar; }