E0575 - Error codes index
Description: Book listing all Rust error codes

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# Error code E0575

Something other than a type or an associated type was given.

Erroneous code example:

    #![allow(unused)]
    fn main() {
    enum Rick { Morty }

    let _: <u8 as Rick>::Morty; // error!

    trait Age {
        type Empire;
        fn Mythology() {}
    }

    impl Age for u8 {
        type Empire = u16;
    }

    let _: <u8 as Age>::Mythology; // error!
    }

In both cases, we're declaring a variable (called `_`) and we're giving it a type. However, `<u8 as Rick>::Morty` and `<u8 as Age>::Mythology` aren't types, therefore the compiler throws an error.

`<u8 as Rick>::Morty` is an enum variant, you cannot use a variant as a type, you have to use the enum directly:

    #![allow(unused)]
    fn main() {
    enum Rick { Morty }

    let _: Rick; // ok!
    }

`<u8 as Age>::Mythology` is a trait method, which is definitely not a type. However, the `Age` trait provides an associated type `Empire` which can be used as a type:

    #![allow(unused)]
    fn main() {
    trait Age {
        type Empire;
        fn Mythology() {}
    }

    impl Age for u8 {
        type Empire = u16;
    }

    let _: <u8 as Age>::Empire; // ok!
    }