error: associated item referring to unboxed trait object for its own trait --> $DIR/object-unsafe-trait-should-use-self-2021.rs:4:13 | LL | trait A: Sized { | - in this trait LL | fn f(a: dyn A) -> dyn A; | ^^^^^ ^^^^^ | help: you might have meant to use `Self` to refer to the implementing type | LL | fn f(a: Self) -> Self; | ~~~~ ~~~~ error[E0038]: the trait `A` cannot be made into an object --> $DIR/object-unsafe-trait-should-use-self-2021.rs:4:13 | LL | fn f(a: dyn A) -> dyn A; | ^^^^^ `A` 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-unsafe-trait-should-use-self-2021.rs:3:10 | LL | trait A: Sized { | - ^^^^^ ...because it requires `Self: Sized` | | | this trait cannot be made into an object... error: associated item referring to unboxed trait object for its own trait --> $DIR/object-unsafe-trait-should-use-self-2021.rs:9:13 | LL | trait B { | - in this trait LL | fn f(a: dyn B) -> dyn B; | ^^^^^ ^^^^^ | help: you might have meant to use `Self` to refer to the implementing type | LL | fn f(a: Self) -> Self; | ~~~~ ~~~~ error[E0038]: the trait `B` cannot be made into an object --> $DIR/object-unsafe-trait-should-use-self-2021.rs:9:13 | LL | fn f(a: dyn B) -> dyn B; | ^^^^^ `B` 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-unsafe-trait-should-use-self-2021.rs:9:8 | LL | trait B { | - this trait cannot be made into an object... LL | fn f(a: dyn B) -> dyn B; | ^ ...because associated function `f` has no `self` parameter help: consider turning `f` into a method by giving it a `&self` argument | LL | fn f(&self, a: dyn B) -> dyn B; | ++++++ help: alternatively, consider constraining `f` so it does not apply to trait objects | LL | fn f(a: dyn B) -> dyn B where Self: Sized; | +++++++++++++++++ error: aborting due to 4 previous errors For more information about this error, try `rustc --explain E0038`.