Traits

Of course traits can also be generic. Here we define one which reimplements the Drop trait as a generic method to drop itself and an input.

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// Non-copyable types.
struct Empty;
struct Null;
// A trait generic over `T`.
trait DoubleDrop<T> {
    // Define a method on the caller type which takes an
    // additional single parameter `T` and does nothing with it.
    fn double_drop(self, _: T);
}
// Implement `DoubleDrop<T>` for any generic parameter `T` and
// caller `U`.
impl<T, U> DoubleDrop<T> for U {
    // This method takes ownership of both passed arguments,
    // deallocating both.
    fn double_drop(self, _: T) {}
}
fn main() {
    let empty = Empty;
    let null  = Null;
    // Deallocate `empty` and `null`.
    empty.double_drop(null);
    //empty;
    //null;
    // ^ TODO: Try uncommenting these lines.
}
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See also:

Drop, struct, and trait