E0198 - Error codes index
Description: Book listing all Rust error codes

# Error code E0198

A negative implementation was marked as unsafe.

Erroneous code example:

    #![allow(unused)]
    fn main() {
    struct Foo;

    unsafe impl !Clone for Foo { } // error!
    }

A negative implementation is one that excludes a type from implementing a particular trait. Not being able to use a trait is always a safe operation, so negative implementations are always safe and never need to be marked as unsafe.

This will compile:

    #![feature(auto_traits)]

    struct Foo;

    auto trait Enterprise {}

    impl !Enterprise for Foo { }

Please note that negative impls are only allowed for auto traits.