Error code E0091
An unnecessary type or const parameter was given in a type alias.
Erroneous code example:
#![allow(unused)] fn main() { type Foo<T> = u32; // error: type parameter `T` is unused // or: type Foo<A,B> = Box<A>; // error: type parameter `B` is unused }
Please check you didn't write too many parameters. Example:
#![allow(unused)] fn main() { type Foo = u32; // ok! type Foo2<A> = Box<A>; // ok! }