mutex_trait.rs

trait A {
    fn a(&self);
}

trait B {
    fn b(&self);
}

trait C {
    fn c(&self);
}

// Implement C for types, which implement A.
impl<T: A> C for T {
    fn c(&self) {
        self.a()
    }
}

// NOTE: Fails to compile.
// Intention: implement trait C for the types, which implement B, but do not implement A.
impl<T: B + !A> C for T {
    fn c(&self) {
        self.b()
    }
}