Use From to convert the inner value of a parametric type

Question

If I have a parametric type like this:

struct Outer<A> {
   inner: A,
}

Is it possible to create an implementation of the From trait for Outer that will convert Outer<A> to Outer<B> if there exists a From that converts A to B?

Something like this (which doesn't work, as far as I can tell):

impl<A, B: From<A>> From<Outer<A>> for Outer<B> {
    fn from(oa: Outer<A>) -> Self {
        Outer {
            inner: oa.inner.into(),
        }
    }
}

I don't think this is (currently) possible, because there's nothing to stop `A` and `B` being the same (which gives rise to a conflict with the blanket reflexive implementation provided by the standard library). Instead, consider providing an inherent conversion method; or perhaps your own `From` trait? — eggyal, Sep 14 '21 at 14:17
@eggyal I don't believe I know what "an inherent conversion method" is? — egerhard, Sep 15 '21 at 13:39
"Inherent" just means an `impl` directly on the type (i.e. not of a trait). So something like `impl Outer { fn convert(self) -> Outer where A: Into { Outer { inner: self.inner.into() } } }` ? — eggyal, Sep 15 '21 at 13:53
Does this answer your question? [How is there a conflicting implementation of \`From\` when using a generic type?](https://stackoverflow.com/questions/37347311/how-is-there-a-conflicting-implementation-of-from-when-using-a-generic-type) — kmdreko, Oct 31 '21 at 03:34

Use From to convert the inner value of a parametric type

0 Answers0