E0573 - Error codes index
Description: Book listing all Rust error codes

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# Error code E0573

Something other than a type has been used when one was expected.

Erroneous code examples:

    #![allow(unused)]
    fn main() {
    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:

    #![allow(unused)]
    fn main() {
    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:

    #![allow(unused)]
    fn main() {
    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:

    #![allow(unused)]
    fn main() {
    enum Wizard {
        Gandalf,
        Saruman,
    }

    trait Isengard {
        fn wizard(w: Wizard) { // ok!
            match w {
                Wizard::Saruman => {
                    // do something
                }
                _ => {} // ignore everything else
            }
        }
    }
    }