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.