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! }