error[E0038]: the trait `Trait` cannot be made into an object --> $DIR/wf-convert-unsafe-trait-obj-box.rs:16:33 | LL | let t_box: Box = Box::new(S); | ^^^^^^^^^^^ `Trait` 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/wf-convert-unsafe-trait-obj-box.rs:6:14 | LL | trait Trait: Sized {} | ----- ^^^^^ ...because it requires `Self: Sized` | | | this trait cannot be made into an object... = help: only type `S` implements the trait, consider using it directly instead = note: required for the cast from `Box` to `Box` error[E0038]: the trait `Trait` cannot be made into an object --> $DIR/wf-convert-unsafe-trait-obj-box.rs:17:15 | LL | takes_box(Box::new(S)); | ^^^^^^^^^^^ `Trait` 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/wf-convert-unsafe-trait-obj-box.rs:6:14 | LL | trait Trait: Sized {} | ----- ^^^^^ ...because it requires `Self: Sized` | | | this trait cannot be made into an object... = help: only type `S` implements the trait, consider using it directly instead = note: required for the cast from `Box` to `Box<(dyn Trait + 'static)>` error[E0038]: the trait `Trait` cannot be made into an object --> $DIR/wf-convert-unsafe-trait-obj-box.rs:15:5 | LL | Box::new(S) as Box; | ^^^^^^^^^^^ `Trait` 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/wf-convert-unsafe-trait-obj-box.rs:6:14 | LL | trait Trait: Sized {} | ----- ^^^^^ ...because it requires `Self: Sized` | | | this trait cannot be made into an object... = help: only type `S` implements the trait, consider using it directly instead = note: required for the cast from `Box` to `Box` error: aborting due to 3 previous errors For more information about this error, try `rustc --explain E0038`.