error[E0038]: the trait `Foo` cannot be made into an object --> $DIR/object-safety.rs:9:12 | LL | let x: &dyn Foo = todo!(); | ^^^^^^^^ `Foo` cannot be made into an object | note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit --> $DIR/object-safety.rs:5:14 | LL | trait Foo { | --- this trait cannot be made into an object... LL | async fn foo(&self); | ^^^ ...because method `foo` is `async` = help: consider moving `foo` to another trait error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0038`.