error[E0038]: the trait `Tr` cannot be made into an object --> $DIR/safety.rs:15:22 | LL | let _: &dyn Tr = &St; | ^^^ `Tr` 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/safety.rs:4:8 | LL | trait Tr { | -- this trait cannot be made into an object... LL | fn foo(); | ^^^ ...because associated function `foo` has no `self` parameter = note: required for `&St` to implement `CoerceUnsized<&dyn Tr>` = note: required by cast to type `&dyn Tr` help: consider turning `foo` into a method by giving it a `&self` argument | LL | fn foo(&self); | +++++ help: alternatively, consider constraining `foo` so it does not apply to trait objects | LL | fn foo() where Self: Sized; | +++++++++++++++++ error[E0038]: the trait `Tr` cannot be made into an object --> $DIR/safety.rs:15:12 | LL | let _: &dyn Tr = &St; | ^^^^^^^ `Tr` 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/safety.rs:4:8 | LL | trait Tr { | -- this trait cannot be made into an object... LL | fn foo(); | ^^^ ...because associated function `foo` has no `self` parameter help: consider turning `foo` into a method by giving it a `&self` argument | LL | fn foo(&self); | +++++ help: alternatively, consider constraining `foo` so it does not apply to trait objects | LL | fn foo() where Self: Sized; | +++++++++++++++++ error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0038`.