These `repr`s have no effect on a struct.
-Adding an explicit `repr(u*)`, `repr(i*)`, or `repr(C)` to an enum suppresses the null-pointer optimization, like:
+Adding an explicit `repr(u*)`, `repr(i*)`, or `repr(C)` to an enum with fields suppresses the null-pointer optimization, like:
```rust
# use std::mem::size_of;
assert_eq!(16, size_of::<MyReprOption<&u16>>());
```
+This optimization still applies to fieldless enums with an explicit `repr(u*)`, `repr(i*)`, or `repr(C)`.
+
## repr(packed)
`repr(packed)` forces Rust to strip any padding, and only align the type to a