error[E0277]: the size for values of type `T` cannot be known at compilation time --> $DIR/issue-27060-2.rs:3:11 | LL | pub struct Bad { | - this type parameter needs to be `Sized` LL | data: T, | ^ doesn't have a size known at compile-time | = note: the last field of a packed struct may only have a dynamically sized type if it does not need drop to be run = help: change the field's type to have a statically known size help: consider removing the `?Sized` bound to make the type parameter `Sized` | LL - pub struct Bad { LL + pub struct Bad { | help: borrowed types always have a statically known size | LL | data: &T, | + help: the `Box` type always has a statically known size and allocates its contents in the heap | LL | data: Box, | ++++ + error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.