Error code E0198

A negative implementation was marked as unsafe.

Erroneous code example:

struct Foo;

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

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 { }
Run

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

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