Error implementing From<T::Foo> for a generic type

1

The following produces a "conflicting implementations" error. Is there any reason it should or is this a bug?

impl<T> std::convert::From<<T as Foo>::Bar> for Error<T>
where
    T: Foo,
{
    fn from(e: <T as Foo>::Bar) -> Error<T> {
        Error::Bar(e)
    }
}
trait Foo {
    type Bar;
}
enum Error<T> where T: Foo {
    Bar(T::Bar)
}
2

Looks like it conflicts with the impl of From<T> for T from std, because as far as the compiler knows, <T as Foo>::Bar could be Error<T> itself.

Hmm... I guess that would technically be impossible, because then Error<T> would be an unconditionally recursive type (trying it got me the error overflow evaluating the requirement `Error<K>: std::marker::Sized` ). But I don't think the compiler includes that as part of its reasoning about conflicting impls.

3

Ah! I didn't think about it being possible to set the associated type to be the same as the impementing type. Thx!

4

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