Something other than a type has been used when one was expected.
Erroneous code examples:
```compile_fail,E0573
enum Dragon {
Born,
}
fn oblivion() -> Dragon::Born { // error!
Dragon::Born
}
const HOBBIT: u32 = 2;
impl HOBBIT {} // error!
enum Wizard {
Gandalf,
Saruman,
}
trait Isengard {
fn wizard(_: Wizard::Saruman); // error!
}
```
In all these errors, a type was expected. For example, in the first error, if
we want to return the `Born` variant from the `Dragon` enum, we must set the
function to return the enum and not its variant:
```
enum Dragon {
Born,
}
fn oblivion() -> Dragon { // ok!
Dragon::Born
}
```
In the second error, you can't implement something on an item, only on types.
We would need to create a new type if we wanted to do something similar:
```
struct Hobbit(u32); // we create a new type
const HOBBIT: Hobbit = Hobbit(2);
impl Hobbit {} // ok!
```
In the third case, we tried to only expect one variant of the `Wizard` enum,
which is not possible. To make this work, we need to using pattern matching
over the `Wizard` enum:
```
enum Wizard {
Gandalf,
Saruman,
}
trait Isengard {
fn wizard(w: Wizard) { // ok!
match w {
Wizard::Saruman => {
// do something
}
_ => {} // ignore everything else
}
}
}
```