Does Rust implement From<Vec<T>> for Vec<U> if I have already implemented From<T> for U?

Question

I have a struct NotificationOption and another struct NotificationOption2 as well as an implementation for From<NotificationOption> for NotificationOption2.

I'm would like to convert Vec<NotificationOption> to a Vec<NotificationOption2>:

struct NotificationOption {
    key: String,
}

struct NotificationOption2 {
    key: String,
}

impl From<NotificationOption> for NotificationOption2 {
    fn from(n: NotificationOption) -> Self {
        Self {
            key: n.key,
        }
    }
}

let options: Vec<NotificationOption> = ...;
let options2: Vec<NotificationOption2> = options.into();

But I get a compiler error:

error[E0277]: the trait bound `Vec<NotificationOption2>: From<Vec<NotificationOption>>` is not satisfied
  --> src/main.rs:22:46
   |
22 |     let options2: Vec<NotificationOption2> = options.into();
   |                                              ^^^^^^^ ---- required by a bound introduced by this call
   |                                              |
   |                                              the trait `From<Vec<NotificationOption>>` is not implemented for `Vec<NotificationOption2>`

Playground link

Answer 1

Seems not, and it makes sense - you assume that the conversion from Vec<NotificationOption> to Vec<NotificationOption2> is to create a Vec<NotificationOption2>, convert the NotificationOption items into NotificationOption2 using .into() and add them to the vector. Rust has no reason to assume this is the conversion and not some other routine.

You also can't implement From generically for a Vec to Vec since your crate didn't define From. You can perhaps create a conversion trait of your own, and implement it generically between Vec<X: Into<Y>> and Vec<Y>.

Answer 2

It doesn't, but it's trivial to implement yourself:

let options2: Vec<NotificationOption2> = options.into_iter().map(|x| x.into()).collect();