src/generics/gen_trait.md

# Traits

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

```rust,editable
// 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.
}
```

### See also:

[`Drop`][Drop], [`struct`][structs], and [`trait`][traits]

[Drop]: https://doc.rust-lang.org/std/ops/trait.Drop.html
[structs]: ../custom_types/structs.md
[traits]: ../trait.md