Why does struct have two unsized fields?

[OvidiusCicero]

Why does this code not compile?

enum Enumeration {
    A,
    B,
}

#[repr(transparent)]
struct NotZeroSized {
    enumerated: Enumeration,
    name: str,
}

I get

error[E0690]: transparent struct needs at most one non-zero-sized field, but has 2
 --> src/lib.rs:7:1
  |
7 | struct NotZeroSized {
  | ^^^^^^^^^^^^^^^^^^^ needs at most one non-zero-sized field, but has 2
8 |     enumerated: Enumeration,
  |     ----------------------- this field is non-zero-sized
9 |     name: str,
  |     --------- this field is non-zero-sized

For more information about this error, try `rustc --explain E0690`.
error: could not compile `playground` due to previous error

but str is not zero sized no?

[semicoleon]

#[repr(transparent)] can only be applied to types with a single value inside of them. The error is saying you can only have one field with size > 0, and you have two fields with size > 0

[quinedot]

If str were zero-sized, you could use #[repr(transparent)]. But it is not zero-sized; it is not Sized at all. That is, the type does not have a statically known size, it has a dynamic size. The size of a str value is the number of bytes it contains, and that varies from str to str.