CODEWITHSUNDEEP
genericsrusttraits
Avba
Avba

Reputation: 15276

how to implement "drop" on a generic struct where T itself implements a type

I have a generic container struct like this:

struct Container<T> {
  data: T,
  key: String
}

I want to implement Drop for Container<T> when T implements an additional trait.

For instance:

trait Cleanup {
  fn clean(&self);
}

I want to implement Drop for Container in the case that T: Cleanup. In my case I have implemented for my concrete type MyStruct:

impl Cleanup for MyStruct { ... }

I tried to confine the Drop impl like so:

impl<T> Drop for Container<T> where T: Cleanup {
  fn drop(&mut self) { self.data.cleanup() ; }
}

But I get this error:

`Drop` impl requires `T: Cleanup` but the struct it is implemented for does not

Upvotes: 0

Views: 889

Answers (1)

Peter Hall
Peter Hall

Reputation: 58785

It's not allowed for Drop to only be implemented for some instantiations of a type. Since your Drop implementation requires that T: Cleanup, you need to make sure that T: Cleanup for every possible instance of Container<T>, i.e. define the struct like this:

struct Container<T: Cleanup> {
    data: T,
    key: String
}

You can see an explanation like this if you follow the link for the full description for E0367, the error code that you got.

Upvotes: 2

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