E0120 - Error codes index
Description: Book listing all Rust error codes

# Error code E0120

Drop was implemented on a trait, which is not allowed: only structs and enums can implement Drop.

Erroneous code example:

    #![allow(unused)]
    fn main() {
    trait MyTrait {}

    impl Drop for MyTrait {
        fn drop(&mut self) {}
    }
    }

A workaround for this problem is to wrap the trait up in a struct, and implement Drop on that:

    #![allow(unused)]
    fn main() {
    trait MyTrait {}
    struct MyWrapper<T: MyTrait> { foo: T }

    impl <T: MyTrait> Drop for MyWrapper<T> {
        fn drop(&mut self) {}
    }

    }

Alternatively, wrapping trait objects requires something:

    #![allow(unused)]
    fn main() {
    trait MyTrait {}

    //or Box<MyTrait>, if you wanted an owned trait object
    struct MyWrapper<'a> { foo: &'a MyTrait }

    impl <'a> Drop for MyWrapper<'a> {
        fn drop(&mut self) {}
    }
    }