error[E0277]: the size for values of type `T` cannot be known at compilation time --> $DIR/union-sized-field.rs:4:12 | LL | union Foo { | - this type parameter needs to be `Sized` LL | value: ManuallyDrop, | ^^^^^^^^^^^^^^^ doesn't have a size known at compile-time | note: required because it appears within the type `ManuallyDrop` --> $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: consider removing the `?Sized` bound to make the type parameter `Sized` | LL - union Foo { LL + union Foo { | help: borrowed types always have a statically known size | LL | value: &ManuallyDrop, | + help: the `Box` type always has a statically known size and allocates its contents in the heap | LL | value: Box>, | ++++ + error[E0277]: the size for values of type `T` cannot be known at compilation time --> $DIR/union-sized-field.rs:9:12 | LL | struct Foo2 { | - this type parameter needs to be `Sized` LL | value: ManuallyDrop, | ^^^^^^^^^^^^^^^ doesn't have a size known at compile-time | note: required because it appears within the type `ManuallyDrop` --> $SRC_DIR/core/src/mem/manually_drop.rs:LL:COL = note: only the last field of a struct may have a dynamically sized type = 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 - struct Foo2 { LL + struct Foo2 { | help: borrowed types always have a statically known size | LL | value: &ManuallyDrop, | + help: the `Box` type always has a statically known size and allocates its contents in the heap | LL | value: Box>, | ++++ + error[E0277]: the size for values of type `T` cannot be known at compilation time --> $DIR/union-sized-field.rs:15:11 | LL | enum Foo3 { | - this type parameter needs to be `Sized` LL | Value(ManuallyDrop), | ^^^^^^^^^^^^^^^ doesn't have a size known at compile-time | note: required because it appears within the type `ManuallyDrop` --> $SRC_DIR/core/src/mem/manually_drop.rs:LL:COL = note: no field of an enum variant may have a dynamically sized type = 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 - enum Foo3 { LL + enum Foo3 { | help: borrowed types always have a statically known size | LL | Value(&ManuallyDrop), | + help: the `Box` type always has a statically known size and allocates its contents in the heap | LL | Value(Box>), | ++++ + error: aborting due to 3 previous errors For more information about this error, try `rustc --explain E0277`.