Why doesn't Error impl Fail?

[radix]

Hi, I'm trying to integrate the failure crate a bit more tightly into a web framework, so that handlers can return Result<_, failure::Error> directly.

This web framework has a trait ResponseError: failure::Fail, and it requires web handlers to return Result<_, E> where E: ResponseError.

I was trying to impl ResponseError for failure::Error, but quickly realized I can't because failure::Error doesn't impl failure::Fail. Given that Error seems to support all of the same behavior that Fail requires, why doesn't it implement that trait?

[Ixrec]

https://github.com/withoutboats/failure/issues/99#issuecomment-348674144

It would be incoherent because of the reflexive impl of From<T> for T and the impl of From<F> For Error where F: Fail.

---

Meta: Would it make sense to add an FAQ to the Failure docs?

[radix]

Ah, okay. Would this be possible with specialization?

I think a good place for a note would be in the documentation for Error, both library and in the guide.

[jimblandy]

https://github.com/withoutboats/failure/issues/99#issuecomment-348674144

This link is now: #99