error[E0277]: the size for values of type `[u8]` cannot be known at compilation time --> $DIR/unsized-union-ice.rs:6:10 | LL | val: std::mem::ManuallyDrop<[u8]>, | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time | = help: within `ManuallyDrop<[u8]>`, the trait `Sized` is not implemented for `[u8]` note: required because it appears within the type `ManuallyDrop<[u8]>` --> $SRC_DIR/core/src/mem/manually_drop.rs:LL:COL = note: no field of a union may have a dynamically sized type = help: change the field's type to have a statically known size help: borrowed types always have a statically known size | LL | val: &std::mem::ManuallyDrop<[u8]>, | + help: the `Box` type always has a statically known size and allocates its contents in the heap | LL | val: Box>, | ++++ + error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0277`.