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# Error code E0600

An unary operator was used on a type which doesn't implement it.

Erroneous code example:

    #![allow(unused)]
    fn main() {
    enum Question {
        Yes,
        No,
    }

    !Question::Yes; // error: cannot apply unary operator `!` to type `Question`
    }

In this case, `Question` would need to implement the `std::ops::Not` trait in order to be able to use `!` on it. Let's implement it:

    #![allow(unused)]
    fn main() {
    use std::ops::Not;

    enum Question {
        Yes,
        No,
    }

    // We implement the `Not` trait on the enum.
    impl Not for Question {
        type Output = bool;

        fn not(self) -> bool {
            match self {
                Question::Yes => false, // If the `Answer` is `Yes`, then it
                                        // returns false.
                Question::No => true, // And here we do the opposite.
            }
        }
    }

    assert_eq!(!Question::Yes, false);
    assert_eq!(!Question::No, true);
    }